2018/19 Waec Gce Jan/Feb Chemistry 3 [Alternative to Practical Work] Questions And Answers Now Out

2 )
Test
I . Solution + NaOH in excess
Ii . Solution + NH 3 in excess
Iii . Solution + BaCl + HCl in excess
Iv. Solution + AgNO 3
Observation
I . White gelatinous precipitate soluble in excess NaOH
Ii . White gelatinous precipitate soluble in excess NH 3
Iii . White precipitate formed with BaCl2 which dissolves in excess HCl
iv . White precipitate formed with AgNO 3

(2bi)
The reagent is the aliphatic monocarboxylic acids that contains one carboxyl group per molecule
[CnH2n+1COOH]
(2bii)
It is observed that they are called fatty acids due to some of them are found in natural fats and oil by changing the -e- ending the corresponding alkane to -oic acid
Pls Draw a table: for Ethanedioic acid(Oxalic acid), Cis-butenedioic(Maleic acid) & 2,3 dihydroxybutanedioic acid(tartaric acid)
Under Ethanedioic acid(Oxalic acid):
COOH
|
CooH
Under Cis-butenedioic(Maleic acid):
H-C-COOH
||
H-C-COOH
Under 2,3 dihydroxybutanedioic acid(tartaric acid):
H
|
HO-C-COOH
|
HO-C-COOH
|
H

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

(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

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