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Nabteb Gce 2017 Chemistry Practical Answers – Nov/Dec Expo
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Posts: 1
chidusky
chidusky (m)
1 year ago
(1a)
(i) Pipette
(ii) burette
(iii) measuring cylinder
(iv) conical flask

(1bi)
(i) By applying an indicator
(ii) By stopping titration when colour change is observed

(1bii)
Phenopthalein

(1ci)
Concentration of B in moldm^-3
Recall that Molar concentration=Mass concentration/Relative molecular mass
ie moldm^-3=gdm^-3/gmol^-1
Therefore Mola conc=8.8/40
=0.22moldm^-3

(1cii)
Conc of A in moldm^-3
CaVa/CbVb=nA/nB
(Ca*24.60)/(0.22*25.00)=1/2
Ca=0.1118moldm^-3

(1ciii)
Molar mass of H2X=Mass conc/RMM
0.1118=3.9/RMM
RMM=3.9/0.1118
=14.884
=15.00 (approximately)
RMMof X=X+2=15
X=15-2
X=13

=======================================


(2ai)
It turns yellow

(2aii)
It oxidizes to form a corrosive brown yellow coating

(2aiii)
A white precipitate is formed

(2aiv)
Colour changes from blue to colourless

(2bi)
C2H2+H2O->C2H4OH
OH^- + C2H2<=>C2H^- + H2O

(2bii)
The laboratory gas mask should be used

(2biii)
CO2, By passingit through Ca(OH)2

(2biv)
Because it heavier than air

(2bv)
When ethyne is bubbledthrough ammonical silver nitrate solution, a yellow-white precipitate of silver acetylide is formed while ethene does not react.

=========================================


(3ai)
Because NH3 reacts with conc. H2SO4 to form ammonium sulphate

(3aii)
Because it is highly soluble in water

(3aiii)
Because it is lighter than air

(3b)
(i) By dissolving in a suitable warm solvent
(ii) By crushing the sample into particles

(3ci)
When PbCO3 is heated, a yellow lead oxide is formed while Pb(NO2)2 is heated to liberate a brown gas of NO2

(3cii)
NH4Cl turns blue litmus red while NaCl isneutral to litmus

(3d)
CO3^2-,HCO3^- and SO4^2-

(3ei)
E-Dessicant
F-Guaze or perforated plate
Example of dessicant is CaSO4

(3eii)
Dessicator is used in the laboratory to preserve moisture sensitive items egCaCl2(Cobalt chloride)

(3eiii)
The dessicator's lid must be tightly closed in order to avoid leakage and can be sealed using silicon greese
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