CHEMISTRY 13th EDITION LABORATORY MANUAL SK015 & SK025 MINISTRY OF EDUCATION MATRICULATION DIVISION
MATRICULATION DIVISION MINISTRY OF EDUCATION MALAYSIA CHEMISTRY LABORATORY MANUAL SEMESTER I & II SK015 & SK025 MINISTRY OF EDUCATION MALAYSIA MATRICULATION PROGRAMME THIRTEENTH EDITION salinan disahkan
i First Printing, 2003 Second Printing, 2004 Third Printing, 2005 (Sixth Edition) Fourth Printing, 2006 (Seventh Edition) Fifth Printing, 2007 (Eighth Edition) Sixth Printing, 2011 (Ninth Edition) Seventh Printing, 2013 (Tenth Edition) Eighth Printing, 2018 (Eleventh Edition) Ninth Printing, 2020 (Twelfth Edition) Tenth Printing, 2022 (Thirteenth Edition) Copyright © 2022 Matriculation Division Ministry of Education Malaysia ALL RIGHTS RESERVED. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system, without the prior written permission from the Director of Matriculation Division, Ministry of Education Malaysia. Published in Malaysia by Matriculation Division Ministry of Education Malaysia, Level 6 – 7, Block E15, Government Complex Parcel E, Federal Government Administrative Centre, 62604 Putrajaya, MALAYSIA. Tel: 603-8884 4083 Fax: 603-8884 4028 Website: www.moe.gov.my Printed in Malaysia by Malaysia National Library Chemistry Laboratory Manual Semester I & II SK015 & SK025 Thirteenth Edition ISBN 978-983-2604-61-7
ii NATIONAL SCIENCE EDUCATION PHILOSOPHY In consonance with the National Education Philosophy, science education in Malaysia nurtures a science and technology culture by focusing on the development of individuals who are competitive, dynamic, robust and resilient and able to master scientific knowledge and technological competency. NATIONAL EDUCATION PHILOSOPHY Education in Malaysia is an on-going effort towards further developing the potential of individuals in a holistic and integrated manner, so as to produce individuals who are intellectually, spiritually and physically balanced and harmonious based on a firm belief in and devotion to God. Such an effort is designed to produce Malaysian citizens who are knowledgeable and competent, who possess high moral standards and who are responsible and capable of achieving a high level of personal well-being as well as being able to contribute to the betterment of the family, society and the nation at large.
iii FOREWORD I am delighted to write the foreword for the Laboratory Manual, which aimed to equip students with knowledge, skills, and the ability to be competitive undergraduates. This Laboratory Manual is written in such a way to emphasise students’ practical skills and their ability to read and understand instructions, making assumptions, apply learnt skills and react effectively in a safe environment. Science process skills such as making accurate observations, taking measurement in correct manner, using appropriate measuring apparatus, inferring, hypothesizing, predicting, interpreting data, and controlling variables are further developed during practical session. The processes are incorporated to help students to enhance their Higher Order Thinking Skills such as analytical, critical and creative thinking skills. These 21st century skills are crucial to prepare students to succeed in Industrial Revolution (I.R.) 4.0. The manipulative skills such as handling the instruments, setting up the apparatus correctly and drawing the diagrams can be advanced through practical session. The laboratory experiments are designed to encourage students to have enquiry mind. It requires students to participate actively in the science process skills before, during and after the experiment by preparing the prereport, making observations, analysing the results and in the science process skills before, during, after the experiment by preparing the pre-report, making observations, analysing the results and drawing conclusions. It is my hope and expectation that this manual will provide an effective learning experience and referenced resource for all students to equip themselves with the skills needed to fulfil the prerequisite requirements in the first-year undergraduate studies. DR HAJAH ROSNARIZAH BINTI ABDUL HALIM Director Matriculation Division
iv CONTENTS Page Students Learning Time (SLT) v Learning Outcomes v Laboratory Safety viii Ethics In The Laboratory xi Preparation For Experiment xi Semester I Experiment Title 1 Determination of the formula unit of a compound 1 2 Acid Base Titration – Determination of the concentration of hydrochloric acid solution 5 3 Determination of the molar mass of a metal 10 4 Charles’ Law and the ideal gas Law 15 5 Chemical Equilibrium 22 6 pH measurement and its applications 29 Semester II Experiment Title 1 Rate of reaction 36 2 Determining the heat of reaction 40 3 Electrochemical cells 44 4 Reactions of aliphatic and aromatic hydrocarbons 49 5 Reactions of hydroxy compounds 54 6 Aldehydes and ketones 58 References 62 Acknowledgements 63
Chemistry Lab Manual Updated: 18/05/2022 v 1.0 Student Learning Time (SLT) Students will be performing the experiment within the time allocated for each practical work. Face-to-face Non face-to-face 2 hour 0 2.0 Learning Outcomes 2.1 Matriculation Science Programme Educational Objectives Upon a year of graduation from the programme, graduates are: 1. Knowledgeable and technically competent in science disciplines study in-line with higher educational institution requirement. 2. Able to apply information and use data to solve problems in science disciplines. 3. Able to communicate competently and collaborate effectively in group work to compete in higher education environment. 4. Able to use basic information technologies and engage in life-long learning to continue the acquisition of new knowledge and skills. 5. Able to demonstrate leadership skills and practice good values and ethics in managing organisations.
Chemistry Lab Manual Updated: 18/05/2022 vi 2.2 Matriculation Science Programme Learning Outcomes At the end of the programme, students should be able to: 1. Acquire knowledge of science and mathematics as a fundamental of higher level education. (MQF LOC i – Knowledge and understanding) 2. Apply logical, analytical and critical thinking in scientific studies and problem solving. (MQF LOC ii – Cognitive skills) 3. Demonstrate manipulative skills in laboratory works. (MQF LOC iii a – Practical skills) 4. Collaborate in group work with skills required for higher education. (MQF LOC iii b – Interpersonal skills) 5. Deliver ideas, information, problems and solution in verbal and written communication. (MQF LOC iii c – Communication skills) 6. Use basic digital technology to seek and analyse data for management of information. (MQF LOC iii d – Digital skills) 7. Interpret familiar and uncomplicated numerical data to solve problems. (MQF LOC iii e – Numeracy skills) 8. Demonstrate leadership, autonomy and responsibility in managing organization. (MQF LOC iii f – Leadership, autonomy and responsibility) 9. Initiate self-improvement through independent learning. (MQF LOC iv – Personal and entrepreneurial skills)
Chemistry Lab Manual Updated: 18/05/2022 vii 10. Practice good values attitude, ethics and accountability in STEM and professionalism. (MQF LOC v – Ethics and professionalism) 2.3 Course Learning Outcome 2.3.1 Chemistry 1 At the end of the course, student should be able to: 1. Explain the fundamental concepts in chemistry. (C2, PLO 1, MQF LOC i) 2. Solve problems with analytical and critical thinking using chemistry facts and principles. (C4, PLO 2, MQF LOC ii) 3. Apply the appropriate scientific laboratory skills in chemistry experiments. (P3, PLO 3, MQF LOC iii a) 4. Analyse numerical problems in chemistry. (C4, PLO 7, MQF LOC iii e) 2.3.2 Chemistry 2 At the end of the course, student should be able to: 1. Explain the fundamental concepts in chemistry. (C2, PLO 1, MQF LOC i) 2. Solve problems with analytical and critical thinking using chemistry facts and principles. (C4, PLO 2, MQF LOC ii) 3. Apply the appropriate scientific laboratory skills in chemistry experiments. (P3, PLO 3, MQF LOC iii a)
Chemistry Lab Manual Updated: 18/05/2022 viii 2.4 Objectives of Practical Sessions The main purpose of the experiment is to give the student a better insight of the concepts of Chemistry discussed in the lectures by carrying out experiments. The aims of the experiments are to enable students to: 1. Learn and practise the necessary safety precautions in the laboratory. 2. Plan, understand and carry out the experiment. 3. Use the correct techniques in handling the apparatus. 4. Acquire scientific skills in measuring, recording and analysing data. 5. Observe, measure and record data by giving consideration to the consistency, accuracy and units of the physical quantities. 6. Determine the errors in various physical quantities obtained in the experiments. 7. Deduce logically and critically the conclusion based on observation and data analysis. 3.0 Laboratory Safety The Science Matriculation Programme requires the students to attend practical classes two hours a week to complete six experiments each semester. In order for the laboratory to be a safe place to work in, students should learn laboratory rules and regulations, including the correct way of using laboratory apparatus and handling of chemicals before starting any experiments.
Chemistry Lab Manual Updated: 18/05/2022 ix Laboratory rules and regulations. 1. Attendance is COMPULSORY. If you are unable to attend any practical class, you should produce a medical certificate or a letter of exemption. 2. Read, understand and plan your experiment before pre-lab sessions and practical classes. 3. Wear shoes, lab coats and safety goggles at all times in the laboratory. 4. Tie long hair or tuck head scarf under your lab coat 5. Do not wear contact lenses during experiments. 6. Foods and drinks are not allowed in the laboratory. 7. Do not perform any unauthorised experiments! Understand and follow the specified procedures for each experiment. 8. Do not waste chemicals. Take only sufficient amount of chemicals needed for your experiments. 9. Replace the lids or stoppers on the reagent bottles or containers immediately after use. 10. Do not remove chemicals from the laboratory. 11. Handle volatile and hazardous compounds in the fume cupboard. Avoid skin contact with all chemicals, wash off any spillages. 12. Clean up spillages immediately. In case of a mercury spillage, do not touch the mercury. Notify your instructor immediately. 13. Ensure there are no flames in the vicinity before working with flammable chemicals 14. NEVER leave an ongoing experiment unattended.
Chemistry Lab Manual Updated: 18/05/2022 x 15. Be aware or familiar with the location and proper way of handling safety equipment, including eyewash, safety shower, fire blanket, fire alarm and fire extinguisher. 16. Turn off bunsen flames when not in use. Notify your instructor immediately of any injury, fire or explosion 17. Do not throw any solid wastes into the sink. Dispose any organic substances in the waste bottles provided. 18. Wash all glassware after use and return the apparatus to its appropriate places. 19. Keep your work area clean and tidy. 20. Notify your instructor immediately of any injury, fire or explosion I have read and understood the laboratory rules and regulations as stated above. I agree to abide by all these rules, follow the instructions and act responsibly at all times. Signature: Date: Name: Practicum: Matric number: Signature Instructor: Date:
Chemistry Lab Manual Updated: 18/05/2022 xi 4.0 Ethics in the laboratory 1. Follow the laboratory rules. 2. Students must be punctual for the practical session. Students are not allowed to leave the laboratory before the practical session ends without permission. 3. Co-operation between members of the group must be encouraged so that each member can gain experience in handling the apparatus and take part in the discussions about the results of the experiments. 4. Record the data based on the observations and not based on any assumptions. If the results obtained are different from the theoretical value, state the possible reasons. 5. Get help from the instructor or the laboratory assistant should any problems arise during the practical session. 5.0 Preparation for experiment 5.1 Pre-lab Sessions. 1. Read and understand the objectives and the theory of the experiment. 2. Think and plan the working procedures properly for the whole experiment. Make sure you have appropriate table for the data. 3. Complete and submit the pre-lab questions provided.
Chemistry Lab Manual Updated: 18/05/2022 xii 5.2 Practical Sessions 1. Check the apparatus provided. 2. Conduct the experiment carefully. 3. Record all measurements and observations made during the experiment. 4. Keep the work area clean and tidy. 5.3 Post-lab Sessions 1. Explain what has been carried out and discuss the findings of the experiment. 2. Introduce the format of report writing as below: Objective ▪ state clearly Theory ▪ write concisely in your own words ▪ draw and label diagram if necessary Procedure ▪ write in passive sentences about all the steps taken during the experiment Results/ Observation ▪ data tabulation with units and uncertainties ▪ data processing (plotting graph, calculation to obtain the results of the experiments and its uncertainties) Discussion ▪ give comments about the experimental results by comparing it with the standard value. ▪ state the source of mistake(s) or error(s) if any as well as any precaution(s) taken to overcome them. ▪ answer all the questions given Conclusion ▪ state briefly the results with reference to the objectives of the experiment Reminder: NO PLAGIARISM IS ALLOWED.
CHEMISTRY 1 SK015
Chemistry Lab Manual – SK015 Updated: 18/05/2022 1 EXPERIMENT 1: DETERMINATION OF THE FORMULA UNIT OF A COMPOUND Objectives At the end of this lesson, students should be able to: i. synthesise a zinc chloride compound; and ii. determine the formula unit of zinc chloride. Introduction One of the main properties of a compound is its chemical composition which can be identified by determining the elements present. A quantitative analysis can be used to determine the composition of an unknown compound. Once the composition of the compound is known, it’s formula unit can be determined. For example, a compound containing 0.1 mol of silver and 0.1 mol of bromine will have a formula unit, AgBr. In this experiment, a simple compound composed of zinc and chlorine will be prepared. Once the mass of zinc and the mass of the compound are known, the mass of chlorine can be determined. Using these masses, the percentage composition of the compound can be calculated and the formula unit can be deduced. Apparatus Chemical Reagents Hot plate Glass rod White tile Crucible tongs 50 mL crucible Analytical balance Measuring cylinder (10 mL) 6 M HCl Zinc powder
Chemistry Lab Manual – SK015 Updated: 18/05/2022 2 Procedure 1. Weigh the crucible and record the exact mass. 2. Place approximately 0.25 g of zinc powder into the crucible and determine the exact mass of zinc powder. 3. Carefully add in 10 mL of 6 M HCl solution into the crucible containing the zinc powder and stir gently with a glass rod. A vigorous chemical reaction will occur and hydrogen gas will be released. 4. If the zinc powder does not dissolve completely, continue adding the acid, 5 mL at a time until all zinc is dissolved. The amount of acid to be used must not exceed 20 mL. 5. Place the crucible on a hot plate in the fume cupboard and heat the content slowly so that the compound does not splatter during the heating process. 6. Heat the compound gently until it is completely dry. Remove the crucible from the hot plate immediately to avoid the compound from melting. (Precaution: Avoid from overheating) 7. Cover the crucible and allow it to cool to room temperature. Then weigh the crucible and the compound. Record the mass. 8. Reheat the crucible to dry the compound. Let it cool to room temperature and then weigh it again. Repeat the procedure until the difference in mass does not exceed 0.02 g. 9. Determine the mass of zinc chloride from the final weight of the sample (the smallest value). Calculate the mass of chlorine in the zinc chloride. 10. Determine the formula unit of zinc chloride. CAUTION ! Carry out this step in a fume cupboard. Do not work near a fire source. Wet hydrogen gas can cause explosions.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 3 POINT TO DISCUSS 1. Explain why the content is not weighed while it is still hot. 2. Explain why the crucible needs to be covered during cooling. 3. Write a balanced equation for the reaction between zinc and hydrochloric acid.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 4 DATA SHEET EXPERIMENT 1: DETERMINATION OF THE FORMULA UNIT OF A COMPOUND RESULTS No. Item Mass (g) 1. Mass of empty crucible 2. Mass of crucible + zinc powder 3. Mass of zinc powder 4. Mass of crucible + zinc chloride: i) First heating ii) Second heating iii) Third heating 5. Mass of zinc chloride 6. Mass of chlorine
Chemistry Lab Manual – SK015 Updated: 18/05/2022 5 EXPERIMENT 2: ACID-BASE TITRATION − DETERMINATION OF THE CONCENTRATION OF HYDROCHLORIC ACID SOLUTION Objectives At the end of this lesson, students should be able to: i. prepare a standard solution of oxalic acid. ii. standardise 0.2 M NaOH solution. iii. determine the concentration of HCl solution. iv. acquire the correct techniques of titration Introduction Titration is a laboratory technique used to determine the concentration of a solution using another solution with a known concentration. Standards in acid-base titrations One of the solutions involved in a titration is used as a standard solution. The standard solution can be classified as either primary or secondary. A primary standard solution is prepared by dissolving an accurately weighed pure solid of a known molar mass in a known volume of distilled water. A primary standard is used to determine the molarity of the other standard solution, known as a secondary standard. For example, oxalic acid, H2C2O4, and potassium hydrogen phthalate, KHC8H4O4 , are two common primary standards used to determine the concentration of bases (secondary standard). The NaOH solution used in titrations need to be standardized because they contain impurities. Solid NaOH is hygroscopic (it absorbs moisture). Thus, it is difficult to obtain its accurate mass. The standardized NaOH becomes the secondary standard and can then be used to determine the concentration of other acids such as HCl acid.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 6 Equivalence point and end point An equivalence point is the point in a titration at which the added titrant reacts completely with the electrolyte according to stoichiometry.To detect this equivalence point, an indicator which produces a change in colour is often used. The point at which the indicator changes colour is called the end point. The end point and equivalence point should ideally be the same. Chemical equations In this acid-base titration, the neutralisation reactions involved are: H2C2O4(aq) + 2NaOH(aq) → Na2C2O4(aq) + 2H2O(l) . . .(1) HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) . . .(2) Apparatus Chemical Reagents Burette Dropper Glass rod White tile Retort stand Filter funnel 50 mL beaker 25 mL pipette Analytical balance 250 mL conical flask 250 mL volumetric flask 50 mL measuring cylinder x M HCl 0.2 M NaOH Distilled water Phenolphthalein Hydrated oxalic acid, H2C2O4.2H2O
Chemistry Lab Manual – SK015 Updated: 18/05/2022 7 Procedure (A) Preparation of standard solution 1. Weigh to the nearest 0.0001 g about 3.00 g of hydrated oxalic acid, H2C2O4.2H2O in a 50 mL beaker. 2. Add approximately 30 mL of distilled water to dissolve the oxalic acid. 3. Transfer the solution into a 250 mL volumetric flask. Rinse the beaker and pour the content into the flask. Add distilled water up to the calibrated mark of the volumetric flask. 4. Stopper and shake the flask to obtain a homogeneous solution. 5. Calculate the concentration of the standard oxalic acid solution. NOTE: Use this solution to standardize the NaOH solution in Part (B). (B) Standardisation of 0.2 M NaOH solution 1. Rinse a burette with a given NaOH solution to be standardized. 2. Fill the burette with the NaOH solution. Ensure there are no air bubbles trapped at the tip. 3. Record the initial burette reading to two decimal places. 4. Pipette 25 mL of oxalic acid solution from Part (A) into a 250 mL conical flask. Add 2 drops of phenolphthalein to the oxalic acid solution. 5. Place a white tile underneath the flask so that any colour change can be clearly observed. 6. Titrate the acid with the NaOH solution from the burette. During the titration, swirl the flask continuously.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 8 7. Rinse the unreacted solutions at the inner wall of the conical flask with distilled water. 8. Upon reaching the end point, a temporary pink solution appears but fades when the solution is swirled. Continue titrating until a pale pink colour persists for more than 30 seconds. This is the end point. 9. Record the final burette reading to two decimal places. 10. Repeat the titration three times. 11. Calculate the molarity of the NaOH solution. (C) Determination of the molar concentration of HCl solution. 1. Pipette 25 mL of a given HCl solution into a 250 mL conical flask. 2. Add two drops of phenolphthalein. 3. Repeat steps 5-9 as in Part (B). 4. Calculate the concentration of HCl. POINT TO DISCUSS Does the addition of water in step 7 (Part B) affect the result of the titration? Explain.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 9 DATA SHEET EXPERIMENT 2: ACID-BASE TITRATION − DETERMINATION OF THE CONCENTRATION OF HYDROCHLORIC ACID SOLUTION RESULTS (A) Preparation of standard oxalic acid solution i. Exact mass of hydrated oxalic acid = ii. Moles of hydrated oxalic acid = iii. Molarity of oxalic acid = (B) Standardisation of 0.2 M NaOH solution Burette reading / mL Gross I II III Final reading Initial reading Volume of NaOH used / mL Average volume of NaOH used = Calculate the molarity of the NaOH solution. (C) Determination of the molar concentration of HCl solution Burette reading / mL Gross I II III Final reading Initial reading Volume of NaOH used / mL Average volume of NaOH used = Calculate the molarity of the HCl solution
Chemistry Lab Manual – SK015 Updated: 18/05/2022 10 EXPERIMENT 3: DETERMINATION OF THE MOLAR MASS OF A METAL Objectives At the end of this lesson, students should be able to: i. standardize the hydrochloric acid solution. ii. determine the molar mass of an alkaline earth metal by back- titration method. Introduction A reactive metal, for example an alkaline earth metal, would readily react with a strong acid such as hydrochloric acid. The general reaction between a metal, M and an aqueous hydrochloric acid, HCl is as follows: M(s) + 2HCI(aq) → MCl2(aq) + H2(g) The molar mass of M can be determined by a back-titration. A back titration is a two-stage analytical technique. The first stage involves the reaction of a metal with an excess amount of acid of a known concentration. In the second stage, the unreacted acid is titrated with a standardized base solution to determine the amount of the remaining excess reactant. In this experiment, the concentration of the acid is initially determined by the normal titration before the reaction with metal M is carried out. M reacts completely according to stoichiometric equation and if the amount of acid used exceeds the amount of metal in terms of equivalence, then the resulting solution would be acidic. The excess acid can be determined by performing back-titration with sodium hydroxide solution. The amount in moles of the reacted metal is determined by comparing the moles of acid before and after the reaction.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 11 Apparatus Chemical Reagents Scissors Dropper White tile Pipette filler Filter funnel Retort stand 50 mL beaker 50 mL burette 25 mL pipette Analytical balance 250 mL conical flask Abrasive cloth no.3 (36) / sandpaper Aluminium oxide Distilled water Phenolphthalein x M Hydrochloric acid, HCl 1.0 M Sodium hydroxide, NaOH, An unknown alkaline earth metal, M Procedure (A) Standardization of HCl solution 1. Rinse a clean burette with 1.0 M NaOH. 2. Fill the burette with 1.0 M NaOH solution. 3. Record the initial burette reading to two decimal places. 4. Pipette 25 mL HCl solution into a 250 mL conical flask. Add 2 drops of phenolphthalein to the acid. 5. Place a piece of white tile underneath the flask. 6. Titrate the acid with the NaOH solution. Swirl the flask continuously. 7. Upon reaching the end point, a temporary pink solution will appear but the colour will fade when it is swirled. Continue titrating until the pale pink colour remains for more than 30 seconds. This is the end point. 8. Record the final reading of the burette.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 12 9. Repeat the titration three times. 10. Calculate the concentration of the HCI solution. (B) Determination of the molar mass of a metal 1. Pipette 25 mL of HCl solution into 2 separate conical flasks. 2. Clean two pieces of metal M, each of approximately 4 cm long, with a piece of abrasive cloth. 3. Weigh accurately the mass of each sample. 4. Cut each sample into smaller pieces. Place the samples separately into the HCl solution. Swirl occasionally until the metal is completely dissolved. 5. Add 2 drops of phenolphthalein. 6. Record the initial burette reading. 7. Titrate the unreacted HCl with the NaOH solution. 8. Record the final burette reading. 9. Repeat titration with the other sample.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 13 DATA SHEET EXPERIMENT 3: DETERMINATION OF THE MOLAR MASS OF A METAL RESULTS 1. Titration of standard HCl solution Concentration of NaOH = ___________ M Volume of HCl = ___________ mL Burette reading / mL Gross I II III Final reading Initial reading Volume of NaOH / mL Average volume of NaOH = 2. Reaction of metal and HCl Mass of metal (sample I) (g) Mass of metal (sample II) (g) 3. Titration of unreacted HCl Burette reading / mL Sample I Sample II Final reading Initial reading Volume of NaOH (mL)
Chemistry Lab Manual – SK015 Updated: 18/05/2022 14 CALCULATION 1. Calculate the molarity of the standard HCl solution. 2. Determine the number of moles of HCl in 25 mL of the standard solution. 3. Calculate the number of moles of the unreacted HCl solution. Sample I: Sample II: 4. Calculate the number of moles of the reacted metal. Sample I: Sample II: 5. Determine the molar mass of metal in each sample. Sample I: Sample II: Average molar mass of metal = _______ 6. By comparing the results with elements in the periodic table, determine the metal M.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 15 EXPERIMENT 4: CHARLES’ LAW AND THE IDEAL GAS LAW Objectives At the end of this lesson, students should be able to: i. verify Charles’ Law. ii. determine the molar mass of a volatile liquid. Introduction Charles’ Law states that the volume of a fixed mass of a given gas is directly proportional to its absolute temperature at constant pressure. The law is written as V T (n, P constant) In this experiment, a quantity of air is trapped between the sealed end of a thick-walled glass tube (with a small cross-sectional area) and a movable plug of mercury. If the glass tube is held upright, the plug of mercury will move to a position where the pressure of the air in the tube is equal to the atmospheric pressure and a small pressure exerted by the plug. Thus, the pressure of the trapped air is constant. The volume, V, of the trapped air is obtained by multiplying the crosssectional area of the tube, A, with the height of the air column, h. V = A x h Assuming that the cross-sectional area is constant, the volume is directly proportional to the height, i.e., V h. Therefore, the height of the air column can be used as a measure of the volume in this experiment. By measuring this height at different temperatures we can determine the relationship between the volume of the trapped air and its temperature at constant pressure. Ideal Gas Equation: By combining the relationships govern by the gas laws, a general equation known as the ideal gas equation can be obtained.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 16 Boyle’s Law Volume of a fixed mass of a given gas is inversely proportional to its pressure at constant temperature. V p 1 (n, T constant) Avogadro’s Principle All gases of equal volume will contain the same number of molecules at the constant temperature and pressure. V n (T, P constant) Charles’ Law Volume of a fixed mass of a given gas is directly proportional to its absolute temperature at constant pressure. V T (n, P constant) Thus, combining the three laws, we get V p nT The above expression can be written as V = P RnT or PV = nRT ...........(1) This is the ideal gas equation and R is called the gas constant. The number of moles, n, n = Molarmass, Mr mass Therefore, the ideal gas equation can also be written as PV = m ( Mr RT ) ..........(2)
Chemistry Lab Manual – SK015 Updated: 18/05/2022 17 Apparatus Chemical Reagents Needle Wire gauze Tripod stand Rubber band Thermometer Bunsen burner Aluminum foil Analytical balance Barometer Retort stand and clamp Charles’ law apparatus 600 mL beaker 100 mL conical flask 100 mL measuring cylinder Stopwatch Ice Methanol Unknown liquid Procedure (A) Charles’ Law 1. Tie a thermometer to a glass tube containing a plug of mercury with a rubber band. The bulb of the thermometer is placed approximately half-way up the column of the trapped air as shown in Figure 4.1. Figure 4.1 Charles’ law apparatus
Chemistry Lab Manual – SK015 Updated: 18/05/2022 18 2. Fill a 100 mL measuring cylinder with tap water. Place the tube and the thermometer into the water until the air column in the tube is immersed. 3. Leave for 5 minutes to ensure that the temperature of the trapped air is equivalent to the temperature of the tap water. 4. Record the temperature and measure the height of the air column. 5. Repeat Steps 2 until 4 using: i. warm water (40 – 50°C) ii. a mixture of ice and water iii. a mixture of ice and 5 mL methanol NOTE: Ensure that the mercury plug does not split into small droplets. (B) Determination of the molar mass of a gas 1. Cover a 100 mL conical flask with a piece of aluminium foil and tie it loosely around the neck with a rubber band as shown in Figure 4.2. Figure 4.2 Figure 4.3
Chemistry Lab Manual – SK015 Updated: 18/05/2022 19 2. Prick a tiny hole in the middle of the foil with a needle. 3. Weigh the apparatus accurately. 4. Remove the foil and place 5.0 mL of the unknown liquid into the flask. 5. Replace the foil and tie it with a rubber band. 6. Clamp the neck of the flask and immerse it into a 600 mL beaker containing water as shown in Figure 4.3. 7. Heat the water until all of the unknown liquid in the flask has vaporised. 8. Record the temperature of the water bath when all the unknown liquid has evaporated. 9. Take out the flask immediately by using the clamp. 10. Wipe the outer wall of the flask and the aluminium foil when the flask is cooled. 11. Weigh the flask with the aluminium foil, rubber band and the condensed unknown liquid. 12. Discard both the foil and the condensed liquid. Fill the flask up to the brim with water and pour it into a measuring cylinder. Record the volume of water. 13. Record the barometric pressure. 14. Calculate the molar mass of the unknown liquid using the ideal gas equation.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 20 DATA SHEET EXPERIMENT 4: CHARLES’ LAW AND THE IDEAL GAS LAW RESULT (A) Charles’ law TABLE 1 Condition Temperature ( 0C) Volume (Height of gas column) (mm) Warm water Tap water Ice-water Ice-methanol 1. Complete TABLE 1. 2. Plot the height of the column, h, against temperature, T, in celsius on a graph paper. Based on the graph, state the relationship between volume and temperature. 3. Extrapolate the line until h = 0, to obtain the absolute zero temperature.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 21 (B) Determination of the molar mass of the gas TABLE 2 No Item Reading 1. Mass of flask + rubber band + cover (g) 2. Mass of flask + rubber band + cover + condensed liquid (g) 3. Mass of condensed liquid (g) 4. Temperature of water bath (oC) 5. Barometric pressure (mm Hg) 6. Volume of flask (mL) 4. Complete TABLE 2. 5. Calculate the molar mass of the unknown liquid.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 22 EXPERIMENT 5: CHEMICAL EQUILIBRIUM Objectives At the end of this lesson, students should be able to: i. study the effect of concentration and temperature on chemical equilibrium. ii. determine the equilibrium constant, Kc, of a reaction. Introduction There are two types of chemical reactions, namely irreversible and reversible. A reversible reaction will reach a dynamic equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction. At this stage, one cannot observe any changes in the system as the concentration of reactants are constant. This does not mean that the reactions have stopped, instead, the reactions are still occurring but at the same rate. The factors that influence chemical equilibrium are: i. concentration ii. temperature iii. pressure (for reactions that involve gases) A change in one of the factors on a system that is already at equilibrium, will cause the reaction to move to the direction that minimizes the effect of change. The direction of the change can be determined by applying Le Chatelier’s Principle. Le Chatelier’s Principle states that if a system at equilibrium is disturbed by a change in temperature, pressure or concentration of one or more components, the system will shift its equilibrium position in such a way so as to counteract the effect of the disturbance. The effect of concentration According to the Le Chatelier’s principle, the change in concentration of any substance in a mixture at equilibrium will cause the equilibrium position to shift in the forward direction or reverse direction to re-attain the equilibrium.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 23 Consider a general reaction as follows: A + B C + D If substance A or B is added to a mixture at equilibrium, the reaction will shift forward to reduce the concentration of A or B until equilibrium is reestablished. On the other hand, if substance C or D is added, the equilibrium will shift in the direction that will reduce the concentration of C or D, i.e. from right to left until equilibrium is re-established. The effect of temperature The effect of temperature on an equilibrium system depends on whether the reaction is exothermic or endothermic. Consider the following system: E + F G + Heat If the forward reaction is exothermic, then the heat released is considered as one of the products. Heating the system will cause the equilibrium to shift in the reverse direction so as to reduce the excess heat. Thus, the concentrations of E and F increase while the concentration of G decreases. However, when the system is cooled, the equilibrium will move forward to increase the heat in the system. The same principle can be applied to explain an endothermic system. In this experiment, you will study the effect of changes in concentration and temperature on two equilibrium systems. You can notice the shift in equilibrium through changes in colour or phases such as precipitation or dissolution.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 24 Apparatus Chemical Reagents Burette Ice bath Test tube Water bath 10 mL pipette 100 mL beaker 100 mL conical flask 10 mL measuring cylinder 100 mL measuring cylinder 6 M HCl 0.2 M CoCl2 2.5 M NaOH 0.1 M KSCN 0.1 M Fe(NO3)3 0.5 M SbCl3 in 6 M HCl Procedure (A) The effect of concentration in the formation of thiocyanoiron(III) complex ion The thiocyanoiron(III) complex ion is formed when iron(III) ion, Fe3+ , is added to the thiocyanate ion, SCN- . The equation for the reaction is Fe3+ (aq) + 2SCN- (aq) [Fe(SCN)2] + (aq) (Yellowish brown) (blood-red) 1. Place 2 mL of 0.1 M Fe(NO3)3 solution and 3 mL of 0.1 M KSCN solution in a 100 mL beaker. 2. Add 50 mL of distilled water to reduce the intensity of the blood red solution. 3. Place approximately 5 mL each of this solution into four test tubes. (a) To the first test tube, add 1 mL of 0.1 M Fe(NO3)3. (b) To the second test tube, add 1 mL of 0.1 M KSCN. (c) To the third test tube, add 6-8 drops of 2.5 M NaOH. (d) The fourth test tube serves as a control. 4. Tabulate the observations.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 25 (B) The Effect of Temperature The reaction between hexaaquocobalt(II) complex ion with chloride ion produces tetrachlorocobalt(II) ion. The equation for the reaction is given below: [Co(H2O)6 ] 2+(aq) + 4Cl- (aq) (pink) [CoCl4 ] 2-(aq) + 6H2O(l) (blue) 1. Place 2 mL of 0.2 M CoCl2 solution into a conical flask. 2. Add 20 mL of 6 M HCl and swirl the flask. 3. A purple solution should form, indicating a mixture of pink and blue. If the solution appears pink, add more HCl; if it is blue, add more distilled water. 4. Divide the purple solution into 3 separate test tubes. (a) Leave one test tube at room temperature. (b) Place the second test tube in an ice bath. (c) Place the third test tube in a water bath at 80 – 90 °C. 5. Record the colour of the solution in each test tube. Remove the second and the third test tubes and leave them at room temperature. Observe the change in colour. POINT TO DISCUSS Determine whether the forward reaction is exothermic or endothermic. Discuss.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 26 (C) Determination of the equilibrium constant. The following reaction is an example of a heterogenous system: SbCl3 (aq) + H2O(l) SbOCl(s) + 2HCl(aq) The expression for the equilibrium constant is: [SbCl ] [HCl] 3 2 Kc = 1. Pipette 5.0 mL of 0.5 M SbCl3 in 6 M HCl into a conical flask. 2. Carefully add distilled water from a burette into the conical flask while swirling until a faint white precipitate is obtained. 3. Record the volume of water added. 4. Calculate the value of the equilibrium constant, Kc. POINT TO DISCUSS Explain why the concentration of pure liquid and solid are excluded from the equilibrium constant expression for a heterogeneous system.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 27 DATA SHEET EXPERIMENT 5: CHEMICAL EQUILIBRIUM RESULT (A) The effect of concentration in the formation of thiocyanoiron(III) complex ion Test tube Experiment Observation I Addition of 1 mL of 0.1M Fe(NO3)3 II Addition of 1 mL of 0.1M KSCN III Addition of 6-8 drops of 10% NaOH (B) The Effect of Temperature Test tube Experiment Observation I At room temperature II 0 ⁰C (in ice bath) III 80- 90 ⁰C
Chemistry Lab Manual – SK015 Updated: 18/05/2022 28 When left at room temperature: Test tube Observation II III (C) Determination of the equilibrium constant Burette reading / mL Observation Initial reading Final reading Volume of water
Chemistry Lab Manual – SK015 Updated: 18/05/2022 29 EXPERIMENT 6: pH MEASUREMENT AND ITS APPLICATIONS Objectives At the end of this lesson, students should be able to: i. use various methods to measure the pH of acids, bases and salts. ii. determine the dissociation constant, Ka, of acetic acid. Introduction pH is a measure of acidity or basicity of a solution. pH is defined as the negative logarithm of hydrogen ion concentration, [H + ]. pH = − log [H + ] ……….(1) The pH scale ranges from 0 to 14. At 25°C, a neutral solution has a pH of 7. An acidic solution has a pH of less than 7 while a basic solution has a pH greater than 7. There are two methods to determine pH in the laboratory. The first method involves the use of indicators such as pH paper and the universal indicator. The second method is using the pH meter. Acids or bases which ionise completely are called strong acids or strong bases. An example of a strong acid is HCl and a strong base is NaOH. Weak acids and weak bases do not ionise completely. An example of a weak acid is acetic acid, CH3COOH, and that of a weak base is ammonia, NH3. Consider the ionisation of a weak acid, HA. HA(aq) H+ (aq) + A-(aq) ……….(2) The equilibrium constant expression for the above reaction is written as: [HA] [H ][A ] + − Ka = ……….(3) where [H + ], [A− ] and [HA] represent the molar concentrations of species that exist at equilibrium. Kais the dissociation constant for acid HA. A similar expression of Kb can be written for weak bases.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 30 One of the methods to determine Ka is by adding a weak acid solution to its conjugated base solution. The product of this process is an acidic buffer solution. The conjugated base is obtained from the salt produced using the titration method. In this method, a known weak acid, HA is divided into two equal portions, X and Y. The first portion, X is titrated with NaOH solution using phenolphthalein as an indicator to detect the formation of a salt solution. A change in colour, from colourless to light pink, indicates the end point. The equation for the reaction is:- OH− (aq) + HA(aq) A− (aq) + H2O(l) ……….(4) In this reaction, HA reacts with NaOH to form NaA and H2 O. NaA ionises completely to form A− and Na + . The number of moles of A− formed is the same as the number of moles of HA in the second portion, Y, which has not been titrated. The second portion of the weak acid HA is added to the conical flask containing the salt NaA. In this mixture, the concentration of HA is equal to the concentration of A− from the salt. Since [A− ] = [HA], and from Equation 3, Ka = [H + ] The value of [H + ] is obtained by measuring the pH; hence the value of Ka can be calculated.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 31 Apparatus Chemical Reagents Burette Test tube pH meter 25 mL pipette 250 mL conical flask Methyl red Methyl orange Alizarin yellow Phenolphthalein Universal indicator 0.1 M NaCl 0.1 M NH4NO3 0.1 M CH3COONa 0.1 M and 1.0 M NH3 0.01 M and 1.0 M HCl 0.1 M and 1.0 M CH3COOH 0.1 M, 0.2 M and 1.0 M NaOH Procedure (A) Determination of pH of acidic and basic solutions 1. (a) Place 2 mL of the following solutions into separate test tubes. i. 0.01 M HCl ii. 1.0 M HCl iii. 0.1 M CH3COOH iv. 1.0 M CH3COOH v. 0.1 M NaOH vi. 0.1 M NH3 Use pH paper to determine the pH of the solutions. (b) Use a pH meter to determine the pH of the following solutions: i. 0.01 M HCl ii. 1.0 M HCl iii. 0.1 M CH3COOH iv. 1.0 M CH3COOH
Chemistry Lab Manual – SK015 Updated: 18/05/2022 32 2. Fill the test tubes with 2 mL of each of the following solution: i. 0.01 M HCl ii. 0.1 M CH3COOH iii. 0.1 M NH3 Add two drops of methyl red to each test tube. Record the observation. Determine the pH range by comparing the colour of the solutions with the chart provided. Repeat step 2 with methyl orange. 3. Fill the test tubes with 2 mL of each of the following solution: i. 0.1 M NaOH ii. 1.0 M NaOH iii. 0.1 M NH3 iv. 1.0 M NH3 Add two drops of alizarin yellow to each test tube. Record the observation. Determine the pH range by comparing the colour of the solutions with the chart provided. (B) Determination of pH of salt solutions 1. Fill the test tube with 2 mL of each of the following solution: i. 0.1 M NaCl ii. 0.1 M CH3COONa iii. 0.1 M NH4NO3 Using pH paper and universal indicator, determine the pH and state whether the salt solutions are acidic, basic or neutral.
Chemistry Lab Manual – SK015 Updated: 18/05/2022 33 (C) Determination of the dissociation constant of a weak acid, Ka 1. Pipette 25 mL of 0.1 M CH3COOH into two conical flasks, X and Y. 2. Add 2 - 3 drops of phenolphthalein into the conical flask X and titrate it with 0.2 M NaOH. When the volume of base reaches 10 mL, add the titrant drop by drop. The end point is reached when the solution becomes pink. Record the initial and the final readings of the burette. 3. Mix the solution in step 2 with 25 mL of 0.1 M CH3COOH in the conical flask Y. Determine the pH of this mixture using a pH meter. 4. Calculate Ka from the value of pH obtained in step 3. POINT TO DISCUSS 1. Calculate the percentage of ionisation of 0.1 M and 1.0 M acetic acid. How does the percentage of ionisation change with its concentration? 2. Refer to the pH value of acetic acid in Part (A). Calculate its Ka and compare this value to that obtained from Part (C).
Chemistry Lab Manual – SK015 Updated: 18/05/2022 34 DATA SHEET EXPERIMENT 6: pH MEASUREMENT AND ITS APPLICATIONS RESULT (A) pH measurements of acid and base solutions Solution Indicator pH paper pH meter Methyl red Alizarin Yellow Methyl orange HCl 0.01 M - 1.0 M - - - CH3COOH 0.1 M - 1.0 M - - - NaOH 0.1 M - - - 1.0 M - - - - NH3 0.1 M - 1.0 M - - - -
Chemistry Lab Manual – SK015 Updated: 18/05/2022 35 (B) pH measurements of salt solutions Salt solution pH paper Universal Indicator Acidic/ Basic/ Neutral NaCl 0.1 M CH3COONa 0.1 M NH4NO3 0.1 M (C) Dissociation constant of a weak acid, Ka Burette reading / mL Data Final reading Initial reading Volume of NaOH used / mL