Waec Gce 2018 Chemistry (practical)Answers -Jan/Feb Expo-Examwaves

CHEMISTRY ANSWERS

(1ai)
Burrette readings/cm3:|titre 1|titre2|titre3
Final readings        |33.20  |49.60 |1.50
Initial readings      |16.40  |16.40 |16.65

(1aii)
Average volume of acid used
= 16.40+16.40+16.65(cm3)/3
=49.45cm3/3
=16.48cm3

(1b)
(I) Concentration of Y(OH)2.XH2O in mol/dm3
Using CAVA/CBVB = a/b
CA= 0.025mol/0.25dm3 = 0.1mol
VA = 16.48cm3
CB = ?
VB = 25.00cm3
a = 1mol
b = 2 moles
.:. CAVA/CBVB =a/b
CB = CAVA*B/VB*a
= 0.1 mol/dm3 * 16.48cm3 * 2 moles / 25.00 * 1 mol
CB = 3.296/25
CB = 0.131mol/dm3

3a)
I)Desiccator- usefor preserving moisture sensitive items
ii)Volumetric flasks are used for precise dilutions and preparation of standard solutions.
iii)Glass rod are used to mix chemicals and liquids for laboratory purposes .

3ii)
i)Amphoteric is Al2O3
ii)Neutral oxide is H2O
3iii)
Crystallization

3b)
1)hno3aq to cuco3 solid. a light blue solid,
precipitates is formed
2)acidified kmno4 to c2h4. c2h4 is oxidized to ethane-1,2-
diol
3)iodine solution to a paste of unripe plantain. a bluish-black color is produced with iodine