IJMB CHEMISTRY
Number 1
a) Procedure:
i) Rinse the burette with solution A and fill it with the same solution. Record the initial reading by recording the upper meniscus of the burette.
ii) Pipette 20 or 25 cm³ of solution B into a clean conical flask and add about 15 cm³ of solution C using a measuring cylinder. Swirl to mix and warm the mixture until it is about to boil.
iii) From the burette, run in solution A into the content of the conical flask until a permanent faint pink color is observed.
iv) Repeat steps (iii) with fresh portions of 20 or 25 cm³ of solution B twice more.
b) Calculation:
i) Calculate the average titre:
Average Titre = (Volume of Solution A for 1st titration + Volume of Solution A for 2nd titration + Volume of Solution A for 3rd titration) / 3
ii) Balanced reaction equation:
MnO4- + C2O4^2- + H+ -> Mn^2+ + CO2 + H2O
iii) Amount in grams per dm³ of solution A:
Given mass of KMnO4 = 0.60 g
Volume of solution A = 250 cm³ = 0.250 dm³
Amount in grams dm³ of solution A = (0.60 g) / (0.250 dm³) = 2.4 g/dm³
iv) Amount in moles per dm³ of solution A:
Molar mass of KMnO4 = 39.10 g/mol + 54.94 g/mol + 4 * 16.00 g/mol = 158.04 g/mol
Amount in moles dm³ of solution A = (0.60 g) / (158.04 g/mol) = 0.00379 mol/dm³
v) Amount in moles of solution A titrated:
From the balanced equation, it is a 1:1 molar ratio between KMnO4 and C2O4^2-.
Amount in moles of solution A titrated = Amount in moles dm³ of solution A = 0.00379 mol/dm³
vi) Amount in moles of solution B consumed:
From the balanced equation, it is a 1:1 molar ratio between KMnO4 and C2O4^2-.
Amount in moles of solution B consumed = Amount in moles of solution A titrated = 0.00379 mol
vii) Amount in moles per dm³ of solution B:
Given that Solution C contains 2 moles/dm³ of H2SO4.
Amount in moles per dm³ of solution B = 2 mol/dm³
viii) Amount in grams per dm³ of solution B:
Molar mass of H2C2O4 (oxalic acid) = 2 * 1.01 g/mol + 2 * 12.01 g/mol + 4 * 16.00 g/mol = 90.04 g/mol
Amount in grams per dm³ of solution B = 2 mol/dm³ * 90.04 g/mol = 180.08 g/dm³
c) Uses of laboratory equipment:
i) Buchner funnel: It is used for vacuum filtration to separate solids from liquids under reduced pressure.
ii) Wash bottle: It is used to dispense small quantities of distilled water or other solvents for rinsing glassware in the laboratory.
iii) Round bottom flask: It is commonly used for heating and boiling reactions in the laboratory due to its rounded shape and even heat distribution.
*IJMB 1d*
A reducing agent is a substance that causes another substance to be reduced in a chemical reaction.
(i) In terms of oxidation number, a reducing agent is a substance that causes another substance to decrease in oxidation number, which means that it gains electrons.
(ii) In terms of electron transfer, a reducing agent is a substance that donates electrons to another substance, which allows the other substance to be reduced.
(iii) In terms of transfer of hydrogen atom, a reducing agent is a substance that donates hydrogen atoms to another substance, which allows the other substance to be reduced.
Number 2
Distinguishing Tests for Cation (Barium Ion, Ba2+):
(a) Flame Test:
Take a small amount of sample A1 (Barium Chloride) and place it on a clean nichrome wire loop.
Hold the wire loop in the flame of a Bunsen burner.
Observations and Inferences:
If a pale green flame is observed, it indicates the presence of the barium ion (Ba2+).
(b) Precipitation Test (Sulfate Test):
Take a small amount of sample A1 and add a few drops of dilute hydrochloric acid (HCl) to it to remove any carbonate ions.
Add a few drops of barium chloride (BaCl2) solution to the sample.
Observations and Inferences:
A white precipitate (barium sulfate, BaSO4) indicates the presence of sulfate ions (SO42-), confirming the presence of the barium ion.
Distinguishing Tests for Anion (Chloride Ion, Cl-):
(a) Silver Nitrate Test:
Take a small amount of sample A1 and add a few drops of dilute nitric acid (HNO3) to it.
Add a few drops of silver nitrate (AgNO3) solution to the sample.
Observations and Inferences:
A white precipitate (silver chloride, AgCl) indicates the presence of chloride ions (Cl-).
(b) Chromyl Chloride Test:
Take a small amount of sample A1 and add a few drops of concentrated sulfuric acid (H2SO4) to it.
Heat the mixture gently and observe the vapors formed.
Observations and Inferences:
If reddish-brown fumes are observed, it indicates the presence of chloride ions (Cl-) forming chromyl chloride (CrO2Cl2).
Identification of Functional Groups in Compounds A2 and A3:
TEST 1 - Litmus Paper:
i) Observations:
No change in blue litmus paper when Compound A2 solution is applied.
No change in blue litmus paper when Compound A3 solution is applied.
Inferences:
Both compounds are likely neutral or neither acidic nor basic.
TEST 2 - Hydrogen Carbonate Solution:
Observations:
No visible reaction with Compound A2 and hydrogen carbonate solution.
No visible reaction with Compound A3 and hydrogen carbonate solution.
Inferences:
Neither Compound A2 nor A3 produces any gas (like CO2) when treated with hydrogen carbonate solution.
TEST 3 - Dinitrophenylhydrazine:
Observations:
No reaction or visible change with Compound A2 and dinitrophenylhydrazine solution.
No reaction or visible change with Compound A3 and dinitrophenylhydrazine solution.
Inferences:
No precipitates or color changes indicate that neither Compound A2 nor A3 contains a carbonyl group.
TEST 4 - Schiff's Reagent:
Observations:
No reaction or visible change with Compound A2 and Schiff's reagent.
No reaction or visible change with Compound A3 and Schiff's reagent.
Inferences:
Absence of a pink or magenta color indicates that neither Compound A2 nor A3 contains a carbonyl group (aldehyde or ketone).
Note: To accurately interpret the results, it is essential to have a complete understanding of the reagents and reactions involved in each test. Always ensure that the samples are handled safely and disposed of properly after the experiments.
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