WEEK 01 - CHEM 401 - LAB GROUP 1 ANIONS (ANACHEM LAB) copy

SAN PEDRO COLLEGE – MAIN CAMPUS

BACHELOR OF SCIENCE IN MEDICAL LABORATORY SCIENCE

ANALYTICAL CHEMISTRY LABORATORY
LECTURER: MA’AM FE BALUYA PASCUA

OUTLINE ○ If base is added, it will react with Ca2+
(Calcium Ion), but since Ca(OH)2 (Calcium
MIDTERMS: WEEK ONE Hydroxide) is a strong base, it will not
precipitate but attract the Ca2+ ions. In this
I. GROUP 1 ANIONS case, equilibrium will shift to the right thus
A. DETECTION OF CARBONATE IONS amplifying the formation of CaCO3 (Calcium
B. REMOVAL OF HEAVY METALS Carbonate)
C. PRECIPITATION OF GROUP I ANION
D. SEPARATION OF GROUP I ANIONS INTO A. FIRST PROCEDURE INVOLVES DETECTION OF
SUBGROUPS CARBONATE IONS
E. IDENTIFICATION OF SULFITE IONS
F. IDENTIFICATION OF ARENITE IONS ● Seven Anions: there are certain precipitating
G. IDENTIFICATION OF ARSENATE IONS reagent that will lead to the formation of the
H. IDENTIFICATION OF PHOSPHATE IONS seven specific ions
I. CONFIRMATION OF OXALATE IONS
J. CONFIRMATION OF FLUORIDE ● Carbonate ions should be analyzed first because
carbonate reagent is always use in the whole
II. ANALYSIS OF GROUP I ANIONS analysis of anions thus creating false positive result
A. FIRST DAY OF ANALYSIS ○ Potassium Chlorate is the carbonate reagent
B. SECOND DAY OF THE ANALYSIS wherein it will serve as a catalyst to make the
1. FIRST PORTION reaction faster and will not alter the solution.
2. SECOND PORTION ○ There are two types of catalyst:
3. THIRD PORTION 1. Inhibitor (Positive Catalyst): substance
4. FOURTH PORTION that will speed up the reaction but will not
C. THIRD DAY OF THE ANALYSIS engrave with the product.
1. FIRST PORTION 2. Retarder (Negative Catalyst): substance
2. SECOND PORTION that will slow down the reaction but will not
engrave with the product.
I. GROUP I ANIONS
● Dilute HCl decomposes carbonate ions and forms
● Group 01 Anions (CO32-, SO32-, AsO2-, AsO43-, carbon dioxide gas thus, the effervescence.
PO43-, C2O42-, F-) ○ Vigorous Effervescence: gas involved is
○ This group of anions forms insoluble Carbon Dioxide are present
salts of calcium in slightly basic solutions.
The precipitating agent is calcium CaCO3 + H3O+↔ Ca2+ + CO2 + H2O
acetate ion.
■ Separate the precipitate and heat ● Chemical Reaction: CO3 + H3O+↔ Ca2+ + CO2↑
gradually by applying the water bath
and stir slowly in one direction in order + H2O
not form bubbles, as well as, so that ● Reagent: dilute HCl
the result will be accurate and the ● Oxidizing agent: KClO3
reaction will not be abrupt ● Confirmed as: carbon dioxide, CO2
● Reaction: vigorous effervescence
● Why basic? Take for example CO3-2 + Ca2+ ↔
B. SECOND PROCEDURE INVOLVES REMOVAL
CaCO3

○ Addition of H+ (acid) gets rid of the CO3-
2 (Carbonate) forming H2CO3 (Carbonic
Acid), meaning the reaction will shift to
the left forming more of CO3-2
(Carbonate) ions.

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SAN PEDRO COLLEGE – MAIN CAMPUS

BACHELOR OF SCIENCE IN MEDICAL LABORATORY SCIENCE

ANALYTICAL CHEMISTRY LABORATORY
LECTURER: MA’AM FE BALUYA PASCUA

OF HEAVY METALS (COMMON: MERCURY, ● Chemical Reaction: H2SO3 + H2O2 + H2O ↔ SO42-
LEAD, CHROMIUM, ZINC AND COPPER) + 2H3O+

● Sodium carbonate precipitates them in their SO42- + Ba2+ ↔ BaSO4↓
carbonate and hydroxide salts with Ksp ranging ● Reagent: Hydrogen peroxide, H2O2
from x 10-14 to 10-20. This can be separated ● Confirmed as: Barium sulfate, BaSO4
from calcium salts since calcium salts have ● Reaction: white precipitate
solubility of 10-9 or less.
○ Sodium Chloride (NaCl): Solubility is the F. IDENTIFICATION OF ARSENITE IONS (AsO2-3)
addition of water wherein by just adding,
complete dissociation occurs ● Addition of hydrogen sulfide (from
thioacetamide:Reagent) produces yellow

C. PRECIPITATION OF GROUP I ANION precipitate (As2S3)
● Chemical Reaction: 2H3AsO3 + 3H2S ↔ As2S3↓+
● PRECIPITATING AGENT: Calcium Acetate,
Ca(C2H3O2)2 6H2O
○ CO3-2 + Ca2+ ↔ CaCO3 ● Reagent: thioacetamide, CH3CSNH2

○ C2O4-2 + Ca2+ ↔ CaC2O4

○ F- + Ca2+ ↔ CaF2 precipi ● Structure:
○ SO3-2 + Ca2+ ↔ CaSO3 tate(s) ● Confirmed as: Arsenic trisulfide, As2S3
○ AsO2-3 + Ca2+ ↔ Ca3(AsO2)2 ● Reaction: yellow precipitate

○ AsO4-3 + Ca2+ ↔ Ca3(AsO4)2 G. IDENTIFICATION OF ARSENATE IONS (AsO4-3)
○ PO4-3 + Ca2+ ↔ Ca3(PO4)2
● Same as arsenite, addition of hydrogen sulfide
■ These are the Calcium Salts (from thioacetamide) produces yellow
precipitate (As2S5) but action is very slow.
D. SEPARATION OF GROUP I ANIONS INTO
SUBGROUPS ● Instead, addition of KI (Potassium
Iodide:Reagent) is used which reduces arsenate
● Addition of Acetic acid (HC2H3O2) dissolves all ion to arsenite, in an acid solution(3M) with the
calcium salts except CaF2 (Calcium Fluoride) liberation of iodide which is color brown or the
and CaC2O4. (Calcium Oxalate) solution turns brown(H3AsO3)

E. IDENTIFICATION OF SULFITE IONS (SO3-2) ● Chemical Reaction: H2AsO4‑ + 3H3O+ ↔ H3AsO3

● First is oxidation to sulfate (SO4-2) by + F2 + 4H2O
hydrogen peroxide/agua oxinada. Then ● Reagent: Potassium Iodide, KI
sulfate is insoluble as BaSO4, thus the white ● Confirmed as: Arsenious acid, H3AsO3
precipitate. ● Reaction: brown solution

● The sulfite ion is oxidized by H2O2 to the sulfate, H. IDENTIFICATION OF PHOSPHATE IONS (PO4-3)
then precipitated as BaSO4, insoluble in strong

acid.

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SAN PEDRO COLLEGE – MAIN CAMPUS

BACHELOR OF SCIENCE IN MEDICAL LABORATORY SCIENCE

ANALYTICAL CHEMISTRY LABORATORY
LECTURER: MA’AM FE BALUYA PASCUA

● Phosphate ions react with ammonium ● It is advantageous if fluoride ions be tested on the
molybdate (Precipitating Agent) in a nitric original sample to make it more sensitive.
acid forming yellow precipitate of ammonium
● Concentrated sulfuric acid (Reagent) dissolves
phosphomolybdate [(NH4)3PO4∙12MoO3]. CaF2 precipitate and produces HF acid. This HF
acid attacks silica thus the etching of the watch
Tartaric acid should be added to make solution
strongly acidic so as not to precipitate arsenate glass. HF + SiO2 (glass) ↔ SiF4 + H2O
ions with molybdate.
● Chemical Reaction: H2PO4- + 12MoO42- + ● Chemical Reaction: CaF2 + 2H3O+ ↔ Ca2+ + 2HF

22H3O+ 3NH4+ ↔ (NH4)2·12MoO3↓ + 34H2O + 2H2O

● Reagent: ammonium molybdate, (NH4)2MoO4 *HF + SiO2 (glass) ↔ SiF4 + H2O
● Confirmed as: ammonium ● Reagent: concentrated sulfuric acid, H2SO4
● Confirmed as: SiF4
phosphomolybdate, (NH4)3PO4·12MoO3 ● Reaction: etching
● Reaction: yellow precipitate(voluminous)

I. IDENTIFICATION OF OXALATE IONS (C2O4-2) Summary
● Chemical Analysis can be better done with the
● Addition of sulphuric acid dissolves CaC2O4
producing oxalic acid. Oxalic acid is a help of a flowchart.
reducing agent reducing permanganate ● Knowing the scenario and creating a good strategy
ions to manganous ions, thus color changes
from purple to colorless or disappearance of gives an idea of what to expect in the analysis
● Selecting appropriate reagents for the analysis
pink color. MnO4-↔ Mn+2 (reduction)
can help identify the anions in question
○ Potassium Permanganate serve as a ● Learning the Solubility Rules and familiarizing
reagent wherein it also serve as a catalyst
and good oxidizing agent wherein the yourself with the Solubility Table can help you
presence of the Permanganate makes it
also good for colorizing. identify the anions present based on the color of

● Chemical Reaction: CaC2O4 + 2H3O+ ↔ Ca2+ their precipitates
● Determining the color of the solution produced as

they react with some reagents also help in

identifying the anions present

+ H2C2O4 + 2H2O

*H2C2O4 + 2MnO4- + 6H3O+ ↔ Mn2+ + 10CO2 +

14H2O

● Reagent: potassium permanganate, KMnO4

● Confirmed as: Manganese(II) or

Manganous ion, Mn2+

● Reaction: colorless

II. ANALYSIS OF GROUP I ANIONS

J. IDENTIFICATION OF FLUORIDE IONS (F-)

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SAN PEDRO COLLEGE – MAIN CAMPUS

BACHELOR OF SCIENCE IN MEDICAL LABORATORY SCIENCE

ANALYTICAL CHEMISTRY LABORATORY
LECTURER: MA’AM FE BALUYA PASCUA

● The anions of group I are distinguished B. SECOND DAY OF THE ANALYSIS
from the other groups in that their calcium
1. Centrifugate from procedure #3 may contain
salts are insoluble in neutral or slightly sulfite, arsenite, arsenate and phosphate ions.
Divide into four portions and test as follows:
basic solution. The group precipitating agent a. FIRST PORTION
- Add 2 drops of concentrated HCl and 5
is calcium acetate solution. drops of Ba(Ac)2. Centrifuge and discard
● The group I anions are divided into two any precipitate which may have formed. To
clear the centrifugate, add 5 drops of H2O2.
subgroups by the action of dilute acetic Formation of white precipitate confirms the
presence of SULFITE ION.
acid. Calcium fluoride and calcium oxalate b. SECOND PORTION
- Add 2 drops of 3M HCl and 2 drops of
are insoluble in 3M HAc, whereas other water. Heat to boiling in a water bath and
add 5 drops of thioacetamide. Immediate
members of the group dissolved. formation of brown (yellow) precipitate
● The soluble subgroups should be analyzed confirms the presence of ARSENITE ION.
c. THIRD PORTION
immediately after the solution is affected. This - Add 2 drops of 3M HCl and heat in a water
bath for 2 minutes. Add a few crystals of KI.
subgroup contains the sulfite and arsenite ions If the solution turns yellow (brown),
presence of ARSENATE ION is indicated.
which may be oxidized to sulfate and arsenate d. FOURTH PORTION
- Add 5 drops of concentrated HNO3 and
by atmospheric oxygen upon standing. 0.2g of solid tartaric acid. Stir the solution
thoroughly and add 5 drops of ammonium
A. FIRST DAY OF THE ANALYSIS molybdate solution. Warm in a water bath
for 1 minute. Formation of a yellow
1. Detection of Carbonate Ion precipitate confirms the presence of
● In a test tube dilute 10 drops of 3M HCl with PHOSPHATE ION.
an equal amount of distilled water and add
0.1g of KClO3. To this mixture add 10 C. THIRD DAY OF THE ANALYSIS
drops of the unknown sample. Vigorous
effervescence indicates presence of 1. Residue from procedure #3 may contain
CARBONATE ION. oxalate and fluoride ions. Wash twice with
water and discard washings. Divide the
2. Count the number of drops of the remaining residues into 2 portions and test as follows:
unknown sample and transfer into another test a. FIRST PORTION
tube. Add an equal amount of distilled water - Add 10 drops of 1.5M H2SO4 and heat
and heat in a water bath for 2 minutes. Now, while stirring in a water bath for 1
add an equal amount (same amount of the minute. Add 2 drops of 0.01M KMnO4
sample) of 1.5M Na2CO3 solution and heat in
a water bath for 10 minutes. Centrifuge and
discard precipitate.

3. To the centrifugate obtained in procedure #2
add 2M Ca(Ac)2 drop by drop until precipitation
is complete (maximum of 15 drops) centrifuge
and discard centrifugate. The residue may
contain insoluble calcium salts of carbonate,
sulfite, arsenite, arsenate, phosphate, oxalate
and fluoride ions. Wash the residue twice with
water and discard washings. To the residue,
add 15 drops of 3M Hac, stir thoroughly and
centrifuge. Separate the centrifugate from the
residue and keep both test tubes inside the
locker.

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SAN PEDRO COLLEGE – MAIN CAMPUS
BACHELOR OF SCIENCE IN MEDICAL LABORATORY SCIENCE

ANALYTICAL CHEMISTRY LABORATORY
LECTURER: MA’AM FE BALUYA PASCUA

solution. Disappearance of the pink
color indicates the presence of
OXALATE ION.
b. SECOND PORTION
- Transfer the residue to a clean, clear
watch glass. Heat watch glass over a
water bath until the residue is dry. Add
1 drop of concentrated H2SO4 to the
dried residue in the watch glass and
continue to heat over a water bath for
5 minutes. Allow to stand for 20
minutes, then wash the glass
thoroughly. Etching of the glass
confirms the presence of FLUORIDE
ION.

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