lab handbook2020

Principles of Inorganic
Chemistry I Laboratory

CHM62-222

Phimphaka Harding School of Science Walailak University

INTRODUCTION

GENERAL CONSIDERATION

Inorganic chemistry is a practical science and an important component in the study of this subject is the
laboratory experience. The experiments in this course will require you to synthesize a range of inorganic
compounds, learning special laboratory skills, notably non-aqueous solution chemistry. In addition, various
spectroscopic techniques will be used to characterize the prepared materials to give you experience in their use
and interpretation. The course objectives are to:

1. Explore the breadth of inorganic chemistry.
2. Learn intermediate laboratory techniques.
3. Develop essential problem solving skills.
4. Make connections between chemical theory and practice.

The laboratory work consists of ten 3-hours sessions starting in 1st week of the semester. The first three sessions
will involve introduction. After this there will be four laboratory sessions each divided into three parts:

• Study of the background and details of the experiment before the lab session so that you understand
what you will have to do. You have to finish the “Pre-lab exercise” and “Risk assessment” before you
attend the lab session.

• The experimental part, conducted under the guidance of several instructors who will be there to help
you with all aspects of the experiment. Note that at the start of each lab there will be only a five minute
presentation just to brief you quickly on the topic of the experiment.

• A report which will be written after the experiment has been completed. The report must include
objective, experimental, results and discussion, and conclusion sections. All reports must be prepared
independently.

For each laboratory session you should bring with you a lab coat, a set of safety glasses and appropriate footwear
for example, covered shoes not flip-flops - these are essential for all chemistry labs. You should also make sure
that for all sessions you have a scientific calculator; the calculator on your mobile will not be good enough.

SAFETY IN CHEMISTRY LABORATORY

Safety in the laboratory is largely a question of common sense and good organization. It is each person’s
individual responsibility to make sure that they work safely. You should familiarize yourself with all the safety
equipment in the lab (fire blankets, fire extinguishers, safety showers etc.) and the procedure in case of fire (fire
exits and meeting point). A good general rule is to think first before you do anything.

In the case of an emergency report the nature and location of the problem to the member of staff in charge. Be
certain to inform other people in the area of the problem and if necessary remove them. If someone is injured
do not move him or her unless s/he is in immediate danger from chemical exposure or fire; then seek medical
attention. Do not panic, instead remain calm. The remaining section details the appropriate action in different
situations:

FIRES

1. If there is a fire in a small vessel (e.g. a flask) it can usually be suffocated by covering the vessel with a
fire blanket. Remove nearby flammable materials to avoid the fire spreading. A fire extinguisher will
normally be operated by the instructor (A water extinguisher should never be used with electrical or
certain chemical fires).

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2. However, if the fire is too large to be easily suffocated or put out with an extinguisher, evacuate the
area and if possible close all doors and windows. When leaving activate the fire alarm and then gather
at the meeting point outside the laboratory building (see below).

3. In the unlikely event that a person’s clothes catch fire, roll on the floor to smoother the flames - do not
run. Afterwards, cover the person with a fire blanket.

4. Should someone be burnt during the fire and if the burn is minor (the skin remains unbroken) the
affected area should be left under a running tap of cold water for 10 minutes. If the burns are more
serious do not attempt to move the person instead seek help from a member of staff.

CHEMICALS
1. Spilt chemicals should be cleaned up immediately. A mop and dustpan and brush are available for this
purpose, simply ask your demonstrator. If the spilt chemical is flammable or toxic inform your
demonstrator of the problem.
2. If chemicals are accidentally splashed into someone’s eyes flush with large amounts of water from the
eyewash fountain. Continue to wash for 15 minutes to make sure that all traces of the chemical are
gone.
3. Should someone swallow chemicals quickly administer 2 - 4 glasses of water and induce vomiting by
tickling the back of the throat.

PERSONAL INJURES
1. If someone is cut wash the wound carefully and remove any traces of glass and then firmly apply a
pressure pad to prevent further bleeding.
2. If a person is electrocuted, do not touch them. Disconnect the power and then seek medical help.
3. In the case of inhalation of fumes remove the victim to fresh air and keep them calm and quiet.
4. If someone is suffering from shock keep the victim lying down, warm, comfortable and with plenty of
fresh air. Reassure them until medical help arrives.
5. Should someone faint lower the victim’s head and raise their feet. Do not administer liquids while they
are unconscious.

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WASTE DISPOSAL

1. Dispose of organic solvents (acetone, ether, toluene etc.) in the appropriate waste solvent container.
2. Strongly acidic or alkaline solutions should be washed down the sink with large volumes of water.
3. Dispose of metal complexes in the waste container provided in the fume cupboard.

The above list has been written to prevent accidents and it is highly unlikely that you will encounter any of the
more serious types of accident if you work in a safe manner.

LABORATORY RAGULATIONS

1. Staff with special responsibilities for safety:
• Ms. Rattana Channgam
• Assoc. Prof. Dr. Phimphaka Harding

2. No work is to be carried out unless a member of staff is present.
3. All persons in laboratories (whether or not they are actually doing practical work) must wear safety

spectacles and laboratory coats. Academic staff supervising undergraduates enforce this rule. In all
laboratories, hair should be secured so that it does not hang below the neck. It is important to wear
suitable clothing, and your footwear must incorporate flat heels, slip resistant soles and uppers fully
enclosing the foot.
4. Foods, drinks, cosmetics and cigarettes must not be taken into or used in areas where chemical
substances are used or kept.
5. Bags and coats should be placed in the lockers provided outside the laboratory and not left in corridors
or on benches.
6. The fire action signs in the laboratory indicate the nearest fire alarm and the emergency exit. There are
fire extinguishers next to the control room. A general fire practice is held once yearly to check the
smooth operation of the procedure so you should ensure that you know where to go in an emergency.
7. Pipetting by mouth is not allowed. Use a bulb or automatic pipette.
8. Do not inhale vapours or make skin contact with any substances. Use gloves where necessary always
remembering that they are semi-permeable.
9. Experiments must be conducted on clean working surfaces; any spillage should be cleaned immediately.
A high standard of tidiness should be maintained at all times. Contaminated surfaces and equipment
must be cleaned as soon as it is practicable after use. The equipment should then be put away. Do not
clutter bench-space with unused equipment and bottles of chemicals.
10. Waste should be disposed of in the appropriate containers: solvents should be placed in either C, H, N,
O-containing waste solvent bottles (Category C Waste), or halogen, sulphur containing waste solvent
bottles (Category D Waste). Heavy metal waste should be placed in the appropriate bottle. Broken
glassware should be washed and placed in the designated glass bin. Solid waste should be dried, placed
in a polythene bag and placed in a solid waste bin.
11. No unauthorised experiments are to be carried out.
12. It is important to ensure that hands are washed and all protective clothing removed before leaving the
laboratory.

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INTRODUCTION ACTIVITY: USING A LAB NOTEBOOK

During practical sessions this course, a lab notebook will be used to record all experimental data. The notebook
should be an A4 glue-bound hard-backed book. This exercise is a paper-based group task to teach how the lab
notebook should be used.

The lab notebook itself will not be used in this first laboratory session. From the second laboratory session of
the year, however, its use is compulsory. Marks will be awarded for continued good use of the notebook
throughout the year.

TASKS
Look at a copy of Notebook Sample Entry 1. This is a bad example of notes made in a lab notebook. Read it
through carefully then discuss with the other members of the group how the lab notebook entry could be
improved. (15 minutes)

Within the group, decide upon a set of good practice guidelines for keeping a good lab notebook during a
laboratory class and write them down on the A3 paper using the marker pen. (10 minutes)

Analyse a copy of Notebook Sample Entry 2 and see how many of your good practice guidelines it satisfies.
Discuss in the group other improvements that could be made to the notebook entry, and use this discussion to
amend the good practice rules appropriately. (10 minutes)

Show the amended and finished set of good practice guidelines to a demonstrator and ask for a copy of the
document entitled ‘Use of a lab notebook’. Read it carefully and check off how many of the good practice
guidelines developed by the group feature in the document. Highlight any omitted guidelines and note them.
(10 minutes).

POST-LAB EXERCISES
Securely stick a neat copy of the ‘Use of a lab notebook’ document into the back cover of the lab notebook.
Copies will be available in the lab or they can be printed out from E-learning. This document should be referred
to throughout the laboratory course to ensure the lab notebook is completed appropriately.

Write your personal details on the first page of your lab notebook following the instructions given in the ‘Use of
a lab notebook’ document. Complete these tasks before your next laboratory session.

USE OF A LAB NOTEBOOK
A lab notebook is a record of all the work carried out in the laboratory. In industry or in academic research, it is
an important legal document that can be used to provide evidence about the discoverer or date of discovery of
new chemicals or processes. In the undergraduate laboratory course it is important to develop the skill (or art!)
of writing a good lab notebook. The records will be needed to generate lab reports at some points in the course,
and the keeping of the lab notebook will be assessed regularly. The lab notebook should be purchased from
Book Center before the start of the course. It needs to last for the term so look after it and ensure that all
additional sheets are glued/taped/stapled securely.

The requirements for keeping a good undergraduate lab notebook are summarised below.

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HOW A GOOD LAB NOTEBOOK IS ORGANISED

The first page of the lab notebook should be used as a cover page and should include name, course, college,
chemistry advisor and email address (so it can be returned in case of loss). The second page should be left blank
to be used as a contents page. This page should be completed as the lab course progresses. Begin to write
experimental data into the lab notebook from the third page onwards. Only write on the right hand side page.
The left hand side page is to be used for a risk assessment of the chemicals used and for noting down other
information e.g. adaptations to the original method. Make sure all pages are numbered and dated. All writing in
the lab notebook should be in ink (blue or black). A ball point pen is better than a fountain pen as it is less likely
to smudge if water is splashed on it.

Lab notebooks need to be looked after carefully. Do not soil them with chemicals as they may transfer hazardous
substances out of the laboratory. In the first year laboratory, there are pull-out lab notebook work stations along
each bench to ensure a chemical-free environment for completing the notebook. Space all work out well on the
page so that the information is clear to anyone reading it.

WHAT TO INCLUDE

The lab notebook is not a copy of the contents of your lab manual. It should expand upon the instructions given
in the lab manual. The experiment title and reference (given in the lab manual) will allow cross referencing of
the experiment notes with the information given in the lab manual. It is important to include the name(s) of any
lab partners or group members and the date so that work can be monitored. If a second page is required, begin
it with the experiment title and reference and the date, before continuing with the experiment notes.

The aim of the experiment should concisely explain the task for that lab session e.g. ‘Aim: to synthesise Fe(acac)3’
If it is a synthesis experiment (where a product is made), a (correct!) chemical equation for the reaction should
be provided.

The experimental plan explains precisely what is to be done in that session. Occasionally, detailed experimental
plans are provided in the lab manual and the lab notebook can state that these were followed directly. If the lab
manual provides only an outline method, a more detailed method should be prepared in the lab notebook before
entry to the lab session so that work can begin immediately. For experiments that require the development of
a method before the lab session begins, editing may be needed during the session if changes are made. These
changes should be clearly noted on the left hand side page alongside the method during the lab session. When
writing a method, use clear language and simple direct statements in a numbered list so that instructions can
be followed easily in the laboratory. Do not use personal pronouns (such as ‘I’ or ‘we’). The experimental plan
section should also be used to note any special safety instructions given in the laboratory manual, or to write a
risk assessment for the chemicals used in the experiment. A diagram should be used to illustrate novel or
unfamiliar apparatus, and should show the cross-section of the equipment. Keep it simple. Label where
appropriate. Do not use diagrams for common apparatus or procedures.

Observations, measurements and data should be recorded immediately and in full (with units, where relevant).
Take the lab notebook to the balances to record masses. Do not use scraps of paper and then transfer the data
to the lab notebook later. Never use Tipp-Ex. Never write over errors; simply cross them out neatly with a single
line and write the correction alongside. Record all observations, measurements and data honestly. The lab
notebook is a record of exactly was observed and measured, not what is predicted to happen or be observed.
When working in pairs or groups, ensure that an individual record of all the observations, measurements and
data, is kept at the time of the experiment. If data are entered directly onto a spreadsheet, ensure that a copy
is printed off and stuck into the lab notebook immediately afterwards. Do not copy data from someone else
after the experiment. If data are to be shared with a partner or group, clearly flag the observations and data as
belonging to someone else. Data should be recorded in a table, where possible, and the table should be written

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in vertical columns using headers and units at the top of each column. Individual cells in the table should only
contain a number; units only appear in headers.

A graph or graphs may be necessary for the experiment. Graphs should be generated from a table of data and
should usually be hand drawn in the first instance. Each graph should be drawn on graph paper, should have the
experiment title and date written on it, and should be stuck in to the lab notebook as soon as possible. Axes
should be labelled with the quantity and the unit. If possible, give error bars on each point. Always use a ruler
to draw straight lines.

The discussion section needs to include clear presentation of any calculations with working that can be followed
by an assessor reading the lab notebook. Use words to explain the meaning of different steps, and include units
throughout. Comments should be made about how the results relate to any hypotheses or how they answer a
question posed in the experimental aims. The conclusion should state the experimental findings and should
include any error analysis and any notes about unusual findings or improvements that could be made if the
experiment were to be performed again.

LAB NOTEBOOK CHECKLIST
This list is not intended to be comprehensive, but it is a very good place to start!

Lab notebook entries for experiments should contain the following before they are handed to a demonstrator
for marking at the end of each session:

• Experiment title and reference number(s).
• The date in full.
• The names of any laboratory partners or group members.
• Aim of the experiment.
• Equations, where required.
• Experimental plan/method and explanation of any experimental decisions.
• Diagram of equipment (if required).
• Observations and comments on the chemistry.
• Tables of data (where required) with column headings and units (no units in cells), either written

directly into the lab notebook or printed off from Excel and securely attached.
• Graph of data (where required), either hand-drawn onto graph paper and stuck in or prepared in Excel,

printed off and attached securely. Remember to include a title and label axes (including units). Graphs
should be self-explanatory and not need notes from other pages of the lab notebook to be understood
by an observer.
• Discussion of key ideas and answers to questions posed in the laboratory manual.
• Conclusion.

Use ink. Work clearly and legibly. Show working.

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NOTEBOOK SAMPLE – ENTRY 1
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NOTEBOOK SAMPLE – ENTRY 2
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ASSESSMENT GUIDE FOR LABORATORY REPORTS

Reports will be assessed against the following criteria, which are not necessarily equally weighted.

Structure Presentation Technical Content Results and Discussion

5 Excellent, very clear, Well written in good Appropriate Critical assessment of

logical subdivision. English, cogent theoretical background the results. Quality of

arguments presented. included. Proper use sample based on data

Conclusions concur made of theory (spectra, errors).

with results obtained, expressions, etc. Graphs neatly plotted

results are clearly and correctly

summarised. interpreted. Extended

interpretation based

on analysis of theory

section.

4 Well organised easy to Clearly laid out, Good grasp of the Results analysed and

follow and a sense of conclusions and necessary theory and assessed in sufficiently

direction throughout. summary evident and its use. critical manner.

clearly written. Evidence of an

appreciation of sources

of error.

3 Satisfactory but some Straightforward to Only the basic theory Satisfactory

loss of way evident. read, satisfactorily behind the experiment assessment of results

written, vagueness or is presented, no and outcome of

hesitancy in evidence of real experiments. Critical

conclusions and understanding. evaluation not overly

summary. evident.

2 No direction, no Somewhat Gaps in understanding Poor analysis of the

subdivision. Lack of disorganised and hard evident from what was results or sample

clarity. to read. Conclusion presented. quality, no attempt to

and summary incorrect assess sources of error

or “off the mark”. or where things may

have gone wrong.

1 No evidence of any Difficult to read; slap No real presentation of No assessment of the

organisation, absence dash presentation, background and its results, no discussion.

of basic understanding, absence of conclusion appreciation.

no coherence. or summary.

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EXPERIMENT 1: PREPARATION OF A

TRANSITION METAL COMPLEX

INTRODUCTION

The study of transition metal complexes, which consist of one or more transition metal ions bonded (by
coordinate bonds) to surrounding ligands, is often described as coordination chemistry and dates back to the
turn of the 20th century. It is an area of research that is very much alive today. Coordination complexes are found
in many aspects of our everyday lives: in nature, in components of industrial chemical processes (e.g. as
catalysts) and in pigments. Examples include haemoglobin and the essential mammalian vitamin B12. At the cores
of these two metalloenzymes lie a transition metal ion (Lewis acid) surrounded by ligands (Lewis bases). It is the
interplay between these two components and consequently of the metal complex as a whole (determined by
the nature of the ligand, metal-ligand bond strength, ligand lability, geometry, and reactivity, etc.) that is the
key to their function.

In this activity, a simple synthetic procedure will be followed to prepare a sample of Fe(acac)3. Acetylacetone
(also known as pentane-2,4-dione) reacts with alkali to produce the acetylacetonate ion (pentane-2,4-dionate,
acac‒). Acetylacetonate is a very versatile ligand for coordination chemistry compounds.

AIMS

• To refresh and extend prior knowledge of coordination chemistry.
• To become more familiar with working in the undergraduate laboratory.
• To carry out a synthetic chemistry experiment (to prepare a transition metal complex).

PRE-LABORATORY EXERCISES

These exercises must be completed at least one hour before the start of the laboratory session. Students who
do not complete the pre-lab exercises will be turned away from the laboratory until the tasks are completed.

1. Ensure that all the post-lab exercises from the first laboratory session are completed. This includes
setting up your lab notebook ready for use.

2. Refresh your knowledge of coordination chemistry by reading through suitable sections of relevant
textbooks, or by reference to https://www.chemguide.co.uk/ (visit ‘Some essential complex ion
chemistry’ and ‘Some essential transition metal chemistry’ in the ‘Inorganic Chemistry’ section. Links

available on E-learning). It will be very helpful to read up on why M ions are acidic in solutionใ

3. Read through the laboratory activity section in the laboratory manual and highlight unfamiliar words
or apparatus.

4. Log in to E-learning and, in the General section, open ‘Foundation Chemistry LabSkills’ and click to
begin. Click on the ‘Equipment Glossary’ or the ‘Reagent Glossary’ at the top of the screen to find the
meaning of any unfamiliar words contained in your laboratory manual.

5. From the Foundation Chemistry LabSkills main menu, select ‘Filtration’. Select ‘Technique’ from the
menu and read through the information, clicking along the progress bar at the bottom to move through.
When complete, click on ‘Gravity Filtration Video’ and watch all stages, then click on ‘Buchner filtration
video’ and watch through. Both of these methods of filtration should be familiar from prior studies,
but, if not, take time to learn about the differences between them and their uses.

6. It is likely that you have used a Bunsen burner for heating in previous practical work. In the
undergraduate laboratory, it is more likely that a hot plate will be used, accompanied by a magnetic

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stirrer bar (also known as a ‘stirrer flea’). To prepare for using this apparatus, open the Chemistry
Interactive Lab Primer, via E-learning. Select the ‘Lab Techniques’ tab and select ‘Heating’ from the
menu. Click on ‘Hot Plates’ and read all information about the use of stirrer hotplates and magnetic
stirrer bars.
7. Prepare the next page of the lab notebook ready for completing the experiment. Refer to the ‘Use of a
lab notebook’ document (which should now be stuck into the back of the notebook). Work out or look
up (e.g. using a textbook or http://www.chemspider.com/) the structure of acetylacetone (acacH) and
acetylacetonate (acac‒) and draw the structure of both into the lab notebook. If required, draw a
diagram of the Buchner filtration apparatus to assist during the laboratory session.

RISK ASSESSMENT

CHEMICAL RISKS SAFETY
Ferric chloride hexahydrate Harmful if swallowed. Irritating to In case of contact with eyes, rinse
skin. Risk of serious damage to immediately with plenty of water.
Acetylacetone (pentane-2,4- eyes. Wear eye/face protection
dione) Flammable, harmful if swallowed. Do not breathe
Sodium hydroxide gas/fumes/vapour/spray. Avoid
Causes burns. contact with skin and eyes.
Dilute hydrochloric acid In case of contact rinse
At this concentration, treat as immediately with plenty of water.
irritant. Wear gloves when handling.
Wear gloves.

LABORATORY ACTIVITY

PART 1: PREPARATION OF Fe(acac)3

Work in pairs but keep individual records in lab notebooks as the experiment proceeds. Show a demonstrator
the prepared lab notebook to confirm completion of the pre-lab exercises.

1. Using a top pan balance, measure out 1.0 g of iron(III) chloride hexahydrate (FeCl36H2O) into a conical
flask (100 cm3). Add a magnetic stirrer bar and add deionised water (15 cm3).

2. In a separate 100 cm3 conical flask mix acetylacetone (acacH) (2 cm3) and NaOH solution (6 cm3;
approximately 2 mol dm-3).

3. Carefully add the acetylacetone / NaOH solution prepared in step 2 to the stirred iron solution and heat
to approximately 50 C using a stirrer hotplate for about 5 minutes.

4. Allow the solution to cool before collecting the precipitate by vacuum filtration (Buchner filtration).
5. Wash the product with deionised water (3 x 5 cm3) on the filter paper and air dry with suction still on.
6. Record observations in the lab notebook throughout. Show a demonstrator that a product has been

isolated.
7. Once dry, weigh the sample on a top pan balance, and record the mass of product obtained. The

acetylacetone and NaOH used in this reaction were in excess and thus the FeCl36H2O determines the
yield. The stoichiometry between FeCl36H2O and Fe(acac)3 is 1:1. Calculate the percentage yield for the
experiment and record it, with working, in the lab notebook. [Hint: do not simply use the mass of
FeCl36H2O to determine the % yield. First determine the number of moles of this starting material. Ask
the demonstrator if you are stuck.]
8. Place the sample in a clean, labelled sample bag (not a bottle!). Wash up all apparatus, thinking carefully
about the disposal of any waste (ask if unsure), and return all equipment. Hand your sample to a
demonstrator for marking, and show them the lab notebook for marking.

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PART 2: INVESTIGATING THE FORMATION OF Fe(acac)3

To understand the chemistry that has just been performed, carry out the following exercises in pairs and discuss
then record the results appropriately (and independently) in the lab notebook. Before beginning, decide upon
an appropriate way to present the results for steps 2-6.

1. Place a small amount (about enough to cover the tip of a spatula) of FeCl36H2O into TestTube 1 and
add approximately 2 cm3 of deionised water. Ensure the solid is dissolved by adding a bung and shaking.
Never cover the top of a test tube with a thumb or a finger to shake. Always use a bung.

2. Add a drop of acetylacetone (from a Pasteur pipette) into Test Tube 2. Add approximately 2 cm3 of
deionised water and swirl. [Note: since this exercise does not involve precise analytical work, 2 cm3 of
deionised water does not need measuring out at all precisely using a pipette or measuring cylinder.
Adding approximately 2 cm height of water to the test tube should suffice.]

3. Measure the pH of each solution by placing a drop of solution onto pH indicator paper and record the
results in the lab notebook.

4. Add two drops (use a Pasteur pipette) of acetylacetone (acacH) from Test Tube 2 into Test Tube 1 (the
iron(III) solution), and record the observations.

5. Slowly (dropwise) add approximately 1 cm3 of 2 mol dm-3 NaOH solution to Test Tube 1, now containing
the FeCl3 and acacH, and record your observations.

6. Slowly (dropwise) add approximately 2 cm3 of dilute HCl solution to the same test tube, and record your
observations.

7. Dispose carefully of any waste (ask if unsure), wash and return all equipment and ensure all power
sockets and hotplates are switched off. Show a demonstrator the clean and tidy workspace, the clean
and tidy fume cupboard and the equipment locker to get signed off.

WRITTEN EXERCISES

Study the results table for the test tube tests and consider the observations and the synthetic experiment that
has been performed when deducing answers to the following questions. Answers should be discussed within the
pair and written individually into the lab notebook.

1. Draw the structure of Fe(acac)3.
2. Write an equilibrium equation to explain the pH that was recorded for the solution of acacH.
3. Explain the effect of the addition of NaOH on this equilibrium, and deduce and explain why NaOH was

added to the acetylacetone solution before it was added to the iron(III) solution in the synthesis.
4. In a solution of FeCl36H2O, the ion [Fe(H2O6]3+ is present. Using the formula of the hexaaqua ion to

begin, give an equilibrium equation, or a series of equilibrium equations, that explain the pH recorded
for the FeCl36H2O solution.
5. Using these equilibrium equations, deduce the chemistry that explains the observation in Step 4 and
the changes observed during Step 5.
6. Deduce the chemistry that occurs in Step 6, above, and explain the observations made.

Show the demonstrator the completed exercises for marking before leaving the laboratory. If any equations
or deductions are insufficient, pairs will be required to stay and re-work the answers.

POST-LAB ASSIGNMENT

The results of this experiment should be typed up into a report and submitted electronically via E-learning within
one week of the end of the laboratory session. Reports should be prepared individually and one report should
be submitted per student. Joint submissions are not accepted.

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The report should show your name, your partner’s name and the title. It should be written in continuous prose
and use the passive voice. It should be written as though the reader has no access to the laboratory manual and
so should be a standalone piece of work. Begin with a short ‘Introduction’ section, including a paragraph
summarising the experiment and some background about coordination chemistry. Do not copy text from the
laboratory manual or any other sources (except your lab notebook!). The ‘Results and Discussion’ section should
summarise the results for each part of the experiment (include weighings recorded to an appropriate number
of decimal places, results tables with appropriate significant figures and all units and appropriate calculations
with working, all presented in an appropriate format. Observations should also be included with the results).
Under each set of results, the appropriate calculations should be performed and any questions answered.
The report should also include an error analysis of the results, and should state any references used. Reports
should be concise. Marks will be penalised for over-long reports. Do not copy out the laboratory manual. Draw
any chemical structures using appropriate software e.g. ChemDoodle or ChemSketch.
Reports must be submitted electronically via E-learning within one week of the end of the laboratory session.
Late submission will score zero marks. This report is worth 15%.

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EXPERIMENT 2: SYNTHESIS OF IRON(III)
EDTA COMPLEX, Na[Fe(EDTA)]3H2O

INTRODUCTION

Soluble iron(III) salts dissolve in water to give a solution of hexaaquairon(III) irons, [Fe(H2O)6]3+.
Ethylenediaminetetraacetic acid has the molecular formula C10H16N2O8 and structural formula
(HOOCCH2)2NCH2CH2N(CH2COOH)2. It is usually abbreviated to EDTA. When dissolved in an alkali such as sodium
hydroxide solution, the four carboxylic acid groups ionize to give a 4- ion. This can be represented by:

EDTA + 4OH- → EDTA4- + 4H2O
EDTA4- is a hexadentate ligand. It forms complexes with many aqueous metal ions. Four oxygen atoms and two
nitrogen atoms bond to the metal ion in an octahedral arrangement. These complexes are often called chelates.
The following reaction takes place when solution of [Fe(H2O)6]3+ and EDTA4- are mixed:

[Fe(H2O)6]3+(aq) + EDTA4-(aq) → [Fe(EDTA)]-(aq) + 6H2O(l)

The complex may be precipitated as a yellow solid with the formula Na[Fe(EDTA)]3H2O.

AIMS

• To prepare an Fe(III) complex, Na[Fe(EDTA)]3H2O.
• To construct a risk assessment for the experiment.
• To recrystallise a metal complex.
• To become more familiar with IR spectroscopy.

PRE-LABORATORY EXERCISES

These exercises must be completed at least one hour before the timetabled start time of the laboratory session.
Students not completing the pre-laboratory task will be turned away from the laboratory until the exercises are
completed. If desired, additional questions posed in the laboratory manual can be answered in the lab notebook
before the session to ensure efficient use of time during the session.

1. Read the instructions in the laboratory manual through carefully and highlight unfamiliar words or
apparatus. Use text books, the internet, LabSkills or the Interactive Lab Primer to look up the meanings
of these unfamiliar terms.

2. Prepare a risk assessment for the experiment in the same way as performed previously in Experiment
1. Use previous risk assessment tables that have been provided in laboratory manuals as a template.
The table should list all the chemicals encountered in the experiment (including solvents, starting

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materials and products), the R and S (Risk and Safety) numbers associated with that compound and the
R and S phrases written out in full. Use the MSDS (Material Safety Data Sheet) documents to identify
the appropriate R and S numbers. You may need to search from the internet. Note that the R and S
numbers are not normally given in your laboratory manual, but they should be included in your own
risk assessments.
3. From the Foundation Chemistry LabSkills main menu, select ‘Recrystallisation’. Select ‘Technique’ from
the menu and read through the information, clicking along the progress bar at the bottom to move
through. When complete, click on ‘Video’ and watch all stages, then click on ‘Safety’ and ‘Test’.
4. Read more about recrystallization technique from the link in E-learning.
5. From the Foundation Chemistry LabSkills main menu, select ‘Instrument Techniques’. Select ‘IR
spectroscopy’ from the menu and read through the information, clicking along the progress bar at the
bottom to move through.
6. Prepare the next page of the lab notebook ready for completing the experiment. Refer to the ‘Use of a
lab notebook’ document (which should now be stuck into the back of the notebook). Work out or look
up (e.g. using a textbook or http://www.chemspider.com/) the structure of acetylacetone (acacH) and
acetylacetonate (acac‒) and draw the structure of both into the lab notebook. If required, draw a
diagram of the Buchner filtration apparatus to assist during the laboratory session.

RISK ASSESSMENT

A risk assessment for this experiment should have been prepared as part of the pre-laboratory exercises, and it
should have been written neatly or printed and stuck in to the lab notebook before arrival at the laboratory
session. This will be checked by a demonstrator before work can begin in the laboratory.

LABORATORY ACTIVITY

Show a demonstrator the prepared lab notebook to confirm completion of the pre-lab exercises. Work in pairs
but keep individual records in lab notebooks as the experiment proceeds.

PART 1: SYNTHESIS OF Na[Fe(EDTA)]3H2O

1. Stand a deionized water wash bottle in an ice bath.
2. Weight out 3.8 g (0.01 mol) of Na2H2EDTA2H2O into a 100 cm3 beaker. Use a measuring cylinder to add

10 cm3 of 1 mol dm-1 sodium hydroxide solution to the beaker. Heat the mixture gently until the solid
dissolves.
3. Weight out 2.5 g (0.009 mol) of iron(III) chloride-6-water into a boiling tube and add 5 cm3 of water.
Shake the tube gently to dissolve the solid. Warming gently will help to dissolve the solid.
4. Pour the iron(III) chloride solution into the beaker and stir the mixture.
5. Warm the mixture gently to evaporate some of the water until a yellow powder precipitates. This may
take about five minutes. Let the mixture cool.
6. Collect the precipitate by vacuum filtration, washing it well with ice-cold water. Wash the product twice
with 2 cm3 ethanol.
7. Lay the filter paper on a watch glass. Cover the solid product with a piece of clean filter paper and leave
it to dry in a fume cupboard at room temperature.
8. Label a sample tube with the name of the product, your name and the date. Weigh the labelled sample
tube and record its mass.
9. Scrape the dried solid into the weighed sample tube. Weigh the tube again. Record its mass.

16

PART 2: CHEMICAL TESTS OF Na[Fe(EDTA)]3H2O

1. With heating, prepare 10 cm3 of 0.1 M Na[Fe(EDTA)]3H2O.
2. Respectively dispense 10 drops of 0.1 M iron(III) chloride solution and 0.1 M sodium iron(III)

ethylenediaminetetraacetate solution into test tubes.
3. Add 10 drops of 0.1 M sodium hydroxide solution to each of the test tubes and record the observations

in a table.
4. Similarly, test both iron(III) chloride and sodium iron(III) ethylenediaminetetraacetate solutions with

0.1 M fluoride and thiocyanate solutions.

0.1 M solution tested 0.1 M Reagent Observation
Fe3+ NaOH
[Fe(EDTA)]- NaOH
Fe3+ KSCN
[Fe(EDTA)]- KSCN
Fe3+ NaF
[Fe(EDTA)]- NaF

5. Determine which ligand, the monodentate ligands or the hexadentate ligand, EDTA4-, binds more
strongly to the iron(III) ions.

PART 3: RECRYSTALIZATION OF Na[Fe(EDTA)]3H2O

1. Place a small amount (about enough to cover the tip of a spatula) of Na[Fe(EDTA)]3H2O into a Test
Tube and add approximately 1 cm3 of water. Ensure the solid is dissolved by shaking. Never cover the
top of a test tube with a thumb or a finger to shake. Record your observations.

2. Repeat the step 1 process using different solvents (EtOH, MeOH, Acetone and hexane).
3. Choose the recrystallisation method that you think is the best to recrystallise 1 g Na[Fe(EDTA)]3H2O.

PART 4: IR SPECTROSCOPIC STUDY

PROCEDURE FOR OBTAINING INFRARED SPECTRA

Several methods can be used to obtain IR spectra, the most common being: KBr pellet, nujol mull, pure
compound (neat), and solution spectra. Water solutions are avoided due to water's strong IR absorptions, which
mask extensive portions of the spectrum, and because it dissolves most types of IR windows. We shall use KBr
pellets to obtain our spectra.

PREPARATION OF KBr DISC

A small amount of compound is ground up well in an agate or alumina mortar and pestle. About 100 times the
amount of KBr is added and mixed with the sample until homogeneous. Perhaps the most common mistake
made here is to use too much of the compound resulting in a cloudy pellet and a lousy spectrum; it is much
better to use too little sample and add more if needed. Just the right amount of the mixture is transferred into
a KBr press, of which there is a variety. The right amount can only be determined by trial and error; it should be
enough to cover the face of the press and result in a semi-transparent disk (transmittance of ≥20% at
4000 cm-1). Apply pressure to the press. Remove the pellet and examine it; it should be semi-transparent to the
eye. If it is too thick you will not obtain a spectrum; if it is too thin you will have to clean up the tiny pieces that
fall out of the press. Practice makes perfect! Do not discard the KBr/sample mixture until the instructor has
certified that a suitable IR has been obtained. When finished, discard in the appropriate waste bottle.

17

WRITTEN EXERCISES

1. The stability constant for [Fe(EDTA)]− is 5 × 1025 dm3 mol−1. Calculate the concentration of Fe3+ ions
when equal volumes of a 0.2 M EDTA4− solution and a 0.2 M Fe3+ solution are mixed together.

2. Which of the following ligands can form chelates: OH−, CN−, H2NCH2CH2NH2, H2NCH2CH2CH3, (COOH)2
and CH3COOH? Put an asterisk at the upper right corner of the coordinating atom(s) in the formula.

3. 30.00 cm3 of a 0.2000 M EDTA solution is added to 20.00 cm3 of an Fe3+ solution. The excess EDTA is
then back-titrated with a 0.1000 M Pb2+ solution. 15.68 cm3 of the Pb2+ solution is consumed. What is
the concentration of the Fe3+ solution?

POST-LAB ASSIGNMENT

The results of this experiment should be typed up into a report and submitted electronically via E-learning within
one week of the end of the laboratory session. Reports should be prepared individually and one report should
be submitted per student. Joint submissions are not accepted.

The report should show your name, your partner’s name and the title. It should be written in continuous prose
and use the passive voice. It should be written as though the reader has no access to the laboratory manual and
so should be a standalone piece of work. Begin with a short ‘Introduction’ section, including a paragraph
summarising the experiment and some background about recrystallisation and IR spectroscopy. Do not copy
text from the laboratory manual or any other sources (except your lab notebook!). The ‘Results and Discussion’
section should summarise the results for each part of the experiment (include weighing recorded to an
appropriate number of decimal places, results tables with appropriate significant figures and all units and
appropriate calculations with working, all presented in an appropriate format. Observations should also be
included with the results).

Under each set of results, the appropriate calculations should be performed and any questions answered
(detailed below).

PART 1 RESULTS AND DISCUSSION
As well as including results and observations with any appropriate comments, you should answer the following
questions:

1. Calculate the theoretical yield and the percentage yield of Na[Fe(EDTA)]3H2O.
2. Why should an excess base be avoided in Step 2 of Part 1 of the Procedure?

PART 2 RESULTS AND DISCUSSION
1. Use the results to determine the strength of the ligands.
2. Compare the results with the spectrochemical series and explain the results.

PART 3 RESULTS AND DISCUSSION
1. Report the solubility of the compound in various solvents.
2. Explain your choice of the recrystallisation method and solvents that you used in part III.
3. Calculate the % recovery for the compound.

PART 4 RESULTS AND DISCUSSION
1. Identify the important peaks in both spectra.
2. Compare the peak position of the same functional group of each spectrum.

18

The report should also include an error analysis of the results, and should state any references used. Reports
should be concise. Marks will be penalised for over-long reports. Do not copy out the laboratory manual. Draw
any chemical structures using appropriate software e.g. ChemDoodle or ChemSketch.
Reports must be submitted electronically via E-learning within one week of the end of the laboratory session.
Late submission will score zero marks. This report is worth 15%.

19

EXPERIMENT 3: PREPARATION OF AND
COMPLEXOMETRIC TITRATION ANALYSIS
OF A 1,2-DIAMINOETHANE COMPLEX OF
NICKEL

INTRODUCTION

Nickel(II) is a good Lewis acid and prefers to bind six Lewis base donor atoms (atoms with lone pair of electrons).
In pure water nickel(II) salt dissolves in water to form [Ni(H2O)6]2+, also known as Ni2+(aq). When ethylenediamine
is added, (abbreviated en; which contains 2 donor atoms per molecule) some or all of the water may be replaced
in [Ni(H2O)6]2+ as shown in Scheme 1.

Scheme 1 Formation of [Ni(en)x(H2O)6-2x]2+.
For a ligand to be useful as a titrant it must form strong complexes with metal ions and the equilibrium between
the metal, ligand and complex must be highly in favour of the formation of the complex, so that the reaction is
quantitative within the limits of error of the experimental procedure used. In other words, the equilibrium must
lie to the right and K must be very large:

K = equilibrium constant (also known as the stability constant in this
context)
Monodentate ligands are not usually suitable. A group of aminopolycarboxylic acid polydentate (or
multidentate) ligands have been found to be ideal. Polydentate ligands are also known as chelating ligands and
are designed to occupy up to 6 coordination positions depending on the requirements of the metal. The most
common ligand titrant is ethylenediaminetetraacetic acid (EDTA).

This molecule can lose two protons to form EDTA2-, which occupies four coordination sites around magnesium
in solution, or EDTA4- (ethylenediaminetetraacetate), which occupies six sites around many first row transition
metals, i.e.

20

Complexes containing polydentate ligands featuring five- or six-membered rings that include the metal centre
are very stable. Thus, the most useful ligand titrants are those that form many five- or six-membered rings, and
in doing so fully saturate the coordination requirements of the metal ion. EDTA4- is one such ligand. It forms a
1:1 complex with many metal ions almost instantly. Note that EDTA forms bonds to metal centres not only
through the nitrogen atoms but also through the oxygen atoms of the acetate (ethanoate) groups.

The stability constant, K, for such a process is:

where = [ ( )]2−
[ ]2+[ ]4−

In general, any ligand that forms a 1:1 complex with a stability constant (K) greater than 107 may be used in
direct complexometric titrations. If the value of K is less, the equilibrium would lie too far to the left and one
would not expect to be able to carry out direct complexometric titration with a standard solution of the
complexing agent.

In this experiment, you will prepare a complex of nickel and use complexometric titration with EDTA to
determine the nickel content of the complex and thus the formula.

AIMS

• To prepare a 1,2-diaminoethane complex of nickel.
• To implement good laboratory practice for handling toxic and carcinogenic chemicals.
• To construct a risk assessment for the experiment.
• To standardise a solution using EDTA in a complexometric titration.
• To analyse a nickel complex of 1,2-diaminoethane using a complexometric titration.

PRE-LABORATORY EXERCISES

These exercises must be completed at least one hour before the timetabled start time of the laboratory session.
Students not completing the pre-laboratory task will be turned away from the laboratory until the exercises are
completed. If desired, additional questions posed in the laboratory manual can be answered in the lab notebook
before the session to ensure efficient use of time during the session.

1. Read carefully through all the information in the laboratory manual for this experiment, including
Appendix 1, and look up any terminology that is unfamiliar.

2. Prepare a risk assessment for the experiment in the same way as performed previously in Experiment
1. Use previous risk assessment tables that have been provided in laboratory manuals as a template.
The table should list all the chemicals encountered in the experiment (including solvents, starting
materials and products), the R and S (Risk and Safety) numbers associated with that compound and the
R and S phrases written out in full. Use the MSDS (Material Safety Data Sheet) documents to identify
the appropriate R and S numbers. You may need to search from the internet. Note that the R and S

21

numbers are not normally given in your laboratory manual, but they should be included in your own
risk assessments.
3. Prepare the lab notebook. Note down the meaning of the term ‘complexometric titration’ when used
in volumetric analysis. Draw the structure of 1,2-diaminoethane in full and state what type of ligand it
is (e.g. monodentate, bidentate, tridentate etc.).

RISK ASSESSMENT

A risk assessment for this experiment should have been prepared as part of the pre-laboratory exercises, and it
should have been written neatly or printed and stuck in to the lab notebook before arrival at the laboratory
session. This will be checked by a demonstrator before work can begin in the laboratory.

LABORATORY ACTIVITY

Show a demonstrator the prepared lab notebook to confirm completion of the pre-lab exercises. Work in pairs
but keep individual records in lab notebooks as the experiment proceeds.

PART 1: PREPARATION OF A 1,2-DIAMINOETHANE-NICKEL COMPLEX

Work in a fume cupboard throughout.

1. Dissolve NiCl26H2O (1.5 g) in deionised water (about 2 cm3).
2. Add 70% 1,2-diaminoethane (ethylenediamine) (1.75 cm3).
3. If necessary (i.e. if any insoluble material remains), filter the solution to remove any nickel oxide

impurities.
4. With gentle stirring slowly evaporate the purple solution to a volume of approximately 2 cm3.
5. Add one further drop of 1,2-diaminoethane, then allow the solution to cool slowly to room

temperature.
6. Cool to ice temperature and await the formation of purple-coloured crystals.
7. Collect the solid product by Buchner funnel, wash twice with acetone and dry in the air.
8. Record the mass of the product.

If the yield is low, further amounts of the product may be obtained from the mother liquor by dropwise addition
of a small volume of ethanol followed by cooling in ice. Repeat this process of addition of alcohol and cooling
until product formation starts again, then leave at ice temperature as long as possible.

PART 2: STANDARDISATION OF EDTA SOLUTION USING Mg2+

1. Add a 20 cm3 aliquot of the MgSO4 standard solution to a 250 cm3 conical flask. Add 2 cm3 of buffer
solution (pH = 10), approximately 40 cm3 deionised water and 2-3 drops of Eriochome Black T indicator
solution.

2. Titrate with the EDTA solution (which is approximately 0.005 M).
3. Repeat until consistent results are obtained (at least 3 times).
4. Calculate the concentration of the EDTA solution, reporting it to an appropriate number of decimal

places. Show your results to the demonstrator before proceeding.

Note 1: Since complex formation does not occur instantaneously, the titration must be carried out slowly near
to the end point.

Note 2: If there are problems determining the end-point, ensure the apparatus is in the fume cupboard and,
during the titration, add 1-2 drops of concentrated ammonia solution.

22

Note 3: For comparison, it is advisable to have solutions at hand that represent the two colours of the indicator.
These may be prepared as follows: To two boiling tubes add an equal volume of the magnesium solution
(approximately 2 cm3), the same volume of water, a few drops of buffer solution (pH = 10) and a drop of the
indicator. Then to one of the tubes add EDTA solution slowly until the indicator changes colour.

PART 3: DETERMINATION OF NICKEL CONTENT OF THE 1,2-DIAMINOETHANE COMPLEX

Work in a fume cupboard.

1. Weigh out accurately about 0.155 g of dried 1,2-diaminoethane complex (prepared in Part 1) into a 100
cm3 conical flask.

2. Carefully add concentrated hydrochloric acid (5 cm3).
3. Boil for 10 minutes. Allow the solution to cool.
4. Carefully dilute with deionised water (approximately 50 cm3).
5. Transfer to a 100 cm3 volumetric flask and transfer all washings. Make up to the mark with deionised

water.
6. Pipette a 20 cm3 aliquot of nickel solution into a 250 cm3 conical flask. Add approximately 100 cm3 of

deionised water and a small quantity of solid Murexide indicator sufficient to give a peach-yellow
colour. Add concentrated ammonia dropwise, testing the pH after additions, until the pH is 7 and the
colour of the solution becomes lemon-yellow. [Hint: at the appropriate pH, the colour changes with
one drop].
7. Titrate with the EDTA solution. After approximately 15 cm3 of EDTA has been added, make the solution
back to pH  10 by dropwise addition of concentrated ammonia. Continue to add EDTA until the colour
changes to magenta (red-purple), adding further drops of concentrated ammonia during the titration
if the colour returns to peach-yellow. Just before the end point, add additional concentrated ammonia
(approximately 5-10 drops).
8. Repeat the titration until consistent results are obtained.

POST-LAB ASSIGNMENT

The results of this experiment should be typed up into a report and submitted electronically via E-learning within
one week of the end of the laboratory session. Reports should be prepared individually and one report should
be submitted per student. Joint submissions are not accepted.

The report should show your name, your partner’s name and the title. It should be written in continuous prose
and use the passive voice. It should be written as though the reader has no access to the laboratory manual and
so should be a standalone piece of work. Begin with a short ‘Introduction’ section, including a paragraph
summarising the experiment and some background about complexometric titration and the indicators used. Do
not copy text from the laboratory manual or any other sources (except your lab notebook!). The ‘Results and
Discussion’ section should summarise the results for each part of the experiment (include weighings recorded
to an appropriate number of decimal places, results tables with appropriate significant figures and all units and
appropriate calculations with working, all presented in an appropriate format. Observations should also be
included with the results).

Under each set of results, the appropriate calculations should be performed and any questions answered
(detailed below).

PART 1 RESULTS AND DISCUSSION

As well as including results and observations with any appropriate comments, you should answer the following
questions:

23

1. The density of ethylenediamine is 0.899 g/mL and the Mr of Ni is 58.69 g mol-1. Determine the molar
ratio of nickel to ethylenediamine in the final product.

2. Suggest a likely formula for the unknown nickel-ethylenediamine complex.
3. Indicate any isomers that could be formed:

PART 2 RESULTS AND DISCUSSION
1. Calculate the concentration of the magnesium sulfate solution and include the working.
2. Determine the concentration of the EDTA solution, including working.

PART 3 RESULTS AND DISCUSSION
1. Report the mass of your nickel complex used in the analysis.
2. Calculate the % Ni in the complex (showing all working) and hence the relative molecular mass and
suggest its formula from your knowledge of possible ligands and counter-ions present.
3. Compare the % Ni found with the theoretical % Ni in likely complexes. The complex is of the general
form MxNiXynH2O, or NiLmX2nH2O, where M = cation, L = neutral ligand, X = anion or anionic ligand (e.g.
halide).
4. Suggest the structure for the complex and indicate clearly which species are ligands bound to the nickel
centre, which species are counter ions, and if there is any solvent of crystallization present.
5. Calculate a % yield for the nickel ethylenediamine complex based on the formula determined and the
mass of nickel chloride used in its preparation.

The report should also include an error analysis of the results, and should state any references used. Reports
should be concise. Marks will be penalised for over-long reports. Do not copy out the laboratory manual. Draw
any chemical structures using appropriate software e.g. ChemDoodle or ChemSketch.

Reports must be submitted electronically via E-learning within one week of the end of the laboratory session.
Late submission will score zero marks. This report is worth 15%.

APPENDIX 1: INDICATORS FOR COMPLEXOMETRIC TITRATIONS

The indicator used in complexometric titrations is itself a ligand (a complexing agent) that forms a distinctly
coloured complex with the metal ion being titrated. Such direct action indicators should possess the following
properties:

1. The free indicator must possess a different colour from the metal/indicator complex.
2. The metal/indicator complex must be formed under the same pH conditions as the metal/EDTA

complex.
3. The indicator must be very sensitive towards the meal ions so that only a small amount of it is

necessary for titration.
4. The metal/indicator compound must be considerably less stable than the metal/EDTA complex, but

not so weak as to dissociate appreciably in the vicinity of the end-point when the concentration of
free metal ions becomes very small. Non-adherence to either condition will lead to diffuse end-points
with high results in the first instance and low in the second.
5. The reaction between the indicator and metal ions must be rapidly reversible.

24

Two indicators used in complexometric titrations are shown below:

Eriochrome Black T, structure I, is the indicator used in the titration with the standard Mg2+ solution. Possible
coordination sites of the indicator are the two imino nitrogens, the two hydroxyl groups and the sulfonic acid
group.
Murexide, structure II, forms a pure yellow complex with nickel(II). The nickel-indicator complex may also be
used as an acid-base indicator to adjust the pH, and is also used in the experiment for this purpose.

25

EXPERIMENT 4: TRANSITION METAL
COMPLEXES OF COBALT(II)

INTRODUCTION

One of the features that make coordination compounds of, in particular, the d-block metals so important is their
so-called ‘complex’ behaviour, something first rationalised by Werner. He studied many aspects of coordination
chemistry, but his most notable contribution is to the understanding of the types of isomerism possible in such
metal complexes, something that will be explored here.
In this experiment, linkage isomers will be prepared. Linkage isomerism is a type of structural (constitutional)
isomerism which can occur when ambidentate ligands form complexes. Ambidentate ligands have two or more
different sites that can be used for attachment to a metal ion, but usually only one is used at any given time.
This experiment is concerned with the NO group, which bonds either through oxygen or nitrogen when it
occupies one coordination position at a transition metal centre. When it bonds through nitrogen it is termed a
nitro ligand and when it bonds through oxygen it is termed a nitrito ligand. Two such complexes,
[Co(NH3)5NO2]Cl2 and [Co(NH3)5ONO]Cl2, are prepared in this experiment.
The reaction sequence that will be used is as follows:

AIMS

• To prepare and compare complexes of cobalt, including nitro- and nitrito isomers.
• To develop an understanding of some of the different ways ligands can bond to metal centres.
• To become more familiar with IR spectroscopy.

PRE-LABORATORY EXERCISES

These exercises must be completed before the experiment, and completed at least one hour before the
timetabled start time of the laboratory session. Students not completing the pre-laboratory task will be turned
away from the laboratory until the exercises are completed. Remember that questions posed in the laboratory
manual can also be answered before the laboratory session, and calculations and equations prepared, to enable
work in the laboratory to be more efficient.

26

1. Read the instructions in the laboratory manual through carefully and highlight unfamiliar words or
apparatus. Use text books, the internet, LabSkills or the Interactive Lab Primer to look up the meanings
of these unfamiliar terms.

2. Prepare a risk assessment for the experiment in the same way as performed previously in Experiment
1. Use previous risk assessment tables that have been provided in laboratory manuals as a template.
The table should list all the chemicals encountered in the experiment (including solvents, starting
materials and products), the R and S (Risk and Safety) numbers associated with that compound and the
R and S phrases written out in full. Use the MSDS (Material Safety Data Sheet) documents to identify
the appropriate R and S numbers. Some have been provided on DUO. Others may need to be searched
for on the internet. Cross reference these R and S numbers with the lists of phrases provided in DUO
and copy them out in full into the table. Note that the R and S numbers are not normally given in your
laboratory manual, but they should be included in your own risk assessments.

3. Considering Part 1 of the experiment, answer the following questions in the lab notebook:
a. Write an equation to represent what happens when ammonia is dissolved in water.
b. Why is this important in the first stage of the synthesis in Part 1?
c. Copy and complete the following equations that describe the formation of [Co(NH3)6]2+
(remembering to balance them):
CoCl2 + 2OH-(aq) + H2O →

[Co(OH2)6](OH)2 + 2OH-(aq) →

[Co(OH)4]2- + NH3 →

d. What are the oxidation states of cobalt in the following?

[Co(NH3)5(OH2)]3+ [Co(NH3)5Cl]2+ [Co(NH3)6]2+

e. Using half-equations, workout a balanced equation for the formation of [Co(NH3)5(OH2)]3+

from [Co(NH3)6]2+ by reaction with H2O2.

f. Give a balanced equation for the synthesis of [Co(NH3)5Cl]2+ from [Co(NH3)5(OH2)]3+ ignoring

the counter anions.

4. From the RSC learning Chemistry main menu, select ‘SpectraSchool’. Select ‘Introduction to

spectroscopy’ from the menu select “Ultraviolet-Visible Spectroscopy (UV-VIS)” and read through the

information, clicking along the progress bar at the bottom to move through.

RISK ASSESSMENT

A risk assessment for this experiment should have been prepared as part of the pre-laboratory exercises, and it
should have been written neatly or printed and stuck in to the lab notebook before arrival at the laboratory
session. This will be checked by a demonstrator before work can begin in the laboratory.

LABORATORY ACTIVITY

Show a demonstrator the prepared lab notebook to confirm completion of the pre-lab exercises. Work in pairs
but keep individual records in lab notebooks as the experiment proceeds. Choose a work area with a free locker
and a fume cupboard to work in, and write the number of these at the top of the lab notebook page for this
experiment.

Work in a fume cupboard for the duration of the experiment. Think carefully about use of stoppers and bungs
to prevent flammable vapours escaping into the laboratory during any transfer of liquids during the experiment.

PART 1: PREPARATION OF [Co(NH3)5Cl]Cl2

The product from Part 1 will be used to prepare the nitro and nitrito complexes. Inform a demonstrator if the
yield is less than 5.5 g. It is essential that the procedure is followed carefully if good yields are to be obtained.

27

1. Work in pairs in a fume cupboard. Dissolve ammonium chloride (5.0 g) in concentrated ammonia (30
cm3) in a 250 cm3 conical flask. Continually agitate this solution whilst adding cobalt(II) chloride
hexahydrate (CoCl26H2O) (10.0 g) in 2-3 g portions, making sure that each portion reacts before the
next portion is added. Initially a precipitate of [Co(NH3)6]Cl2 will form with the evolution of heat.

2. To the warm slurry/solution add, with care, 30% hydrogen peroxide (8 cm3) in small portions (with
efficient stirring). This results in a vigorous exothermic reaction with effervescence. A deep red solution
of [Co(NH3)5(OH2)]3+ should form (sometimes this may look brown, which is not a problem).

3. Cool in an ice bath, then slowly add concentrated hydrochloric acid (30 cm3). Heat the reaction mixture
gently with stirring until a purple product precipitates (typically after 20-30 minutes) from a blue-green
supernatant liquid. Do not allow the solution to boil. When the reaction is complete the supernatant
liquid should be deep blue (to see this, let the mixture settle for a few seconds).

4. Cool to ambient temperature, and filter to obtain the solid product. Wash with several portions of ice
cold water, then with a small quantity of acetone before drying in the air. The product should be a dry
powder. If it is still wet, re-wash the sample with acetone on a Buchner filter until free from water. Do
not proceed with a wet solid. Record the mass of product obtained. Show the product to a
demonstrator.

PART 2: PREPARATION OF [Co(NH3)5NO2]Cl2, THE NITRO-ISOMER

1. Working in a fumehood, dissolve [Co(NH3)5Cl]Cl2 (2.5 g) in a mixture of concentrated ammonia solution
(6 cm3) and water (50 cm3) by heating at the boiling point. Rapidly filter the hot solution through a glass
funnel, cool the filter in an ice bath and acidify slightly to about pH 6 (check with indicator paper using
a glass rod and white tile) by the addition of dilute hydrochloric acid.

2. Add sodium nitrite (3.0 g) to the cold solution, and heat the resultant mixture until the red precipitate
that initially forms completely re-dissolves. Continue heating until the solution is dark yellow-brown in
colour.

3. Cool the dark yellow-brown solution and then add concentrated hydrochloric acid (15 cm3). Cool in ice
for at least half an hour. Collect the brown-yellow crystals by filtration. Wash the product with a small
quantity of acetone, then dry in the air. Record the mass of the product and determine the percentage
yield (based on the amount of [Co(NH3)5Cl]Cl2 used). Give a balanced equation for the formation of the
product. Place the product in an appropriately labelled sample bag and hand in to a demonstrator for
marking.

PART 3: PREPARATION OF [Co(NH3)5ONO]Cl2, THE NITRITO-ISOMER

1. Dissolve [Co(NH3)5Cl]Cl2 (2.5 g) in a mixture of water (50 cm3) and conc. ammonia (6 cm3) with heating
as in Part 2. Filter the resultant solution, cool in ice then neutralise the filtrate with dilute hydrochloric
acid (6 M). This step is absolutely critical to the success of the preparation. Use pH paper, a white tile
and a glass rod to test the solution. A final pH of 6 can be tolerated.

2. Add sodium nitrite (2.5 g) and then 2.5 cm3 of a 1:1 mixture of water and concentrated hydrochloric
acid (Laboratory prepare this solution in advance for students). Cool in ice for at least half an hour, then
filter the red precipitate that gradually forms.

3. Wash the product with ice-cold water and a small volume of acetone before drying in the air. Record
the mass of the product and determine the percentage yield (based on the amount of [Co(NH3)5Cl]Cl2
used). Write the balanced equation for the reaction of NaNO2 with concentrated HCl and thus construct
a balanced equation for the formation of [Co(NH3)5ONO]2+ from [Co(NH3)5Cl]2+. Show the lab notebook
to the demonstrator for marking. Place the product in an appropriately labelled sample bag and hand
in to a demonstrator for marking.

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Ensure that the lab notebook has been checked, samples have been handed in and apparatus has been washed
up and put away. Tidy all work areas. Have the work areas checked by a demonstrator before you leave the
laboratory.

PART 4: UV-VIS SPECTROSCOPIC STUDIES

1. Prepare 25 mL the 0.1 M solution of [Co(NH3)5Cl]Cl2, [Co(NH3)5NO2]Cl2 and [Co(NH3)5ONO]Cl2.
2. Run a scan on each of the solutions above between the wavelengths of 1100 nm to 300 nm.

POST-LAB ASSIGNMENT

The results of this experiment should be typed up into a report and submitted electronically via E-learning within
one week of the end of the laboratory session. Reports should be prepared individually and one report should
be submitted per student. Joint submissions are not accepted.

The report should show your name, your partner’s name and the title. It should be written in continuous prose
and use the passive voice. It should be written as though the reader has no access to the laboratory manual and
so should be a standalone piece of work. Begin with a short ‘Introduction’ section, including a paragraph
summarising the experiment and some background about structural isomer and UV-Vis spectroscopy. Do not
copy text from the laboratory manual or any other sources (except your lab notebook!). The ‘Results and
Discussion’ section should summarise the results for each part of the experiment (include weighing recorded to
an appropriate number of decimal places, results tables with appropriate significant figures and all units and
appropriate calculations with working, all presented in an appropriate format. Observations should also be
included with the results).

Under each set of results, the appropriate calculations should be performed and any questions answered
(detailed below).

PART 1 RESULTS AND DISCUSSION
As well as including results and observations with any appropriate comments, you should answer the following
questions:

1. Calculate the theoretical yield and the percentage yield of [Co(NH3)5Cl]Cl2.
2. Draw structure of [Co(NH3)5Cl]Cl2.

PART 2 RESULTS AND DISCUSSION
1. Calculate the theoretical yield and the percentage yield of [Co(NH3)5NO2]Cl2 and [Co(NH3)5ONO]Cl2.
2. Draw the structures of [Co(NH3)5NO2]Cl2 and [Co(NH3)5ONO]Cl2.
3. Explain the conditions that control the structures of these two complexes.

PART 3 RESULTS AND DISCUSSION
1. Compare the absorption band of those three complexes and try to explain the spectra.

The report should also include an error analysis of the results, and should state any references used. Reports
should be concise. Marks will be penalised for over-long reports. Do not copy out the laboratory manual. Draw
any chemical structures using appropriate software, e.g. ChemDoodle or ChemSketch.

Reports must be submitted electronically via E-learning within one week of the end of the laboratory session.
Late submission will score zero marks. This report is worth 15%.

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