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
(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
(v) Repeat and 4 twice more using a fresh portions of A
(vi) Calculate the average titre.
(vii) Balance the following redox reaction
(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
A. You are provided with sample
(a) Preliminary test:
(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
Volume of pipette
Indicator used – Starch soluble
1st Titration (cm3)
2nd Titration (cm3)
3rd Titration (cm3)
Volume of solution B used
Iodine is oxidized
Iodine is reduced
Multiply (i) by 2 and (ii) by 3
(b) (i) Amount (mols) of I2 used
of solution B contains 0.10mols Na2S2O3
of solution B (titre value) will contain
= 2.887 mol Na2S2O3
(II) Amount (mols) of I2 used
2.887 mols S2O3
I2 = 1.443 mol I2
(III) Concentration (moldm-3
) of I2 in solution A
of solution A (volume of pipette) contains 1.443 mol I2
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
+ 10I- + 16H+
5I2 + 2Mn2+
– mol I2
Also 1 mol I2 2mols S2O3
5mols I2 10mols S2O3
Thus 2mols MnO4
2- 1mol MnO4
2.887 mols S2O3
= 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 =
C (i) It is not colourless before and after titration
(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
iii. Flame test
Colorless gas, pungent and fuming in air
No characteristic coloration
hydrolyzed by moisture
or alkali metal present
Colourless gas, with a pungent smell with
oranged-red solid left.
Deep blue precipitate
iii. Dirty green Precipitate Precipitate of ( )
brown on standing
iv. White precipitate Chloride precipitate AgCl
Sample ( )( )
Formation of yellow crystals
Efferverscence occurse which turns lime
A sweet fruity smell evolves of an ester Alkanoic acid function confirmed.