2019 IJMB CHEMISTRY PRACTICAL QUESTIONS & ANSWERS

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CHEMISTRY PRACTICAL QUESTIONS & ANSWERS

Solution A Contains of Sodium Thiosulphate 
in of solution. 
Solution B: contains of potassium trioxoiodate(V) 
in of solution.
Solution C: contains weight per volume of potassium Iodide ( ) solution
Solution D: 1 molar solution of Hydrochloric acid 
Indicator: Starch Soluble

(1a) PROCEDURE
(i) Put solution A into the burette.
(ii) Pipette of solution B into a clean conical flask and add of each of solution C and D using 
a measuring cylinder. Swirl to mix
(iii) From the burette, run solution A into the conical flask until it turns pale yellow.
 Add drops of starch soluble indicator into the conical flask and continue until the titration reaches a 
colorless end.
(v) Repeat and 4 twice more using a fresh portions of A
(vi) Calculate the average titre.
(vii) Balance the following redox reaction

(1b) DEDUCTIONS
(i) Calculate the amount in moles of KIO3 in each titration.
(ii) Calculate the amount in moles of Na2S2O3 in in of solution A
(iii) The value of in the formula

(1c) Explain why the following steps were taken in the experiment 
(i) Why of solution D was added to step II of the procedure.
(ii) Why the starch indicator was added not at the beginning but close to the end.
(2a) Carry out the following test and record your observation and inferences clearly, using the normal laboratory 
format. Credit will be given for careful observations clearly recorded and explanatory note to account for the 
observed reactions. 
A. You are provided with sample 
( ) 
(a) Preliminary test: 
(i) Appearance. 
(ii) Heat small amount of the sample in a dry test tube and test for any gas evolved. 
(iii) Moisten a small amount of the sample with a drop of concentrated HCl and heat in a non-luminous 
flame, using a clean spatula.

(2b) Take small portions of the sample in a test tube and in each case carry out the following tests: 
(i) Add concentrated 
to the solid sample and test for any gas evolved. Heat the residue 
(ii) Dissolve sample in water, add dropwise potassium ferricyanide solution. 
(iii) Dissolve sample in water, add dropwise and then excess aqueous sodium hydroxide solution. 
(iv) Dissolve sample in water, add dilute and then silver nitrate solution

(2c) You are provided with sample 
Carry out one (1) confirmatory test each for the functional groups present in 
the sample.
Volume of pipette 
Indicator used – Starch soluble

Burette Readings
1st Titration (cm3)
2nd Titration (cm3)
3rd Titration (cm3)
Final 
Initial 
Volume of solution B used

(iii)

(iv)

( )
Iodine is oxidized

( )
Iodine is reduced
Multiply (i) by 2 and (ii) by 3

(b) (i) Amount (mols) of I2 used 
1000cm
3
of solution B contains 0.10mols Na2S2O3
28.87cm3
of solution B (titre value) will contain

S2O3
2-
= 2.887 mol Na2S2O3
(II) Amount (mols) of I2 used
2mols S2O3
2- 
2.887 mols S2O3
2

I2 = 1.443 mol I2
(III) Concentration (moldm-3
) of I2 in solution A 
25cm
3
of solution A (volume of pipette) contains 1.443 mol I2
1000cm
3
of solution A will contain

mol I2 = 0.05773moldm-3
(IV) Amount (mols)of KI formed 
1 mole I2 2 mol KI 
1.443 mol I2 1.443 2 mol KI = 2.886 mol KI 
(v)Amount (mol) of pure KMnO4 used
2MnO4

+ 10I- + 16H+
5I2 + 2Mn2+
+ 8H2O
2mol MnO4
– mol I2
Also 1 mol I2 2mols S2O3
2-
2mol MnO4

5mols I2 10mols S2O3
2-
Thus 2mols MnO4

10mols S2O3
2

5mols S2O3
2- 1mol MnO4
2.887 mols S2O3
2
– 2.887

mols MnO4

= 5.774 mol MnO4

(V)Amount (g) of pure KMnO4
Amount (mol) = ( )

Molar Mass of KMnO4 = 158
Amount (g) of KMnO4 = 5.774 158 = 0.09123g
(vii) Purity =

=

= 2.64%
C (i) It is not colourless before and after titration
(ii) Standardization 
(iii) Iodometry Titration
(iv)Iodine gas can escape reducing the amount of (mols) of iodine produced
(v) From +4 to +7
It is oxidized
(iv) HCl will react with KI and also reduces the oxidizing power of KMnO4

TEST OBSERVATION INFERENCE
Sample 
i. Appearance 
ii. 
iii. Flame test 
Brownish/Green Powder
Colorless gas, pungent and fuming in air
No characteristic coloration

hydrolyzed by moisture

or alkali metal present
B.

( )

Colourless gas, with a pungent smell with 
oranged-red solid left. 
Deep blue precipitate
Volatile HCl
present
iii. Dirty green Precipitate Precipitate of ( ) 
turning 
brown on standing
iv. White precipitate Chloride precipitate AgCl

Sample ( )( )
Formation of yellow crystals 
present
Efferverscence occurse which turns lime 
water milky
Gas is 
from 
. COOH 
function present
A sweet fruity smell evolves of an ester Alkanoic acid function confirmed.

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