2017 Neco Gce Chemistry Practical Expo Answers


1ai)
Methyl Orange
Reason:- Titration of strong acid against base
1aii)Yellow
1aiii)Hydrochloricacid
1aiv)2HCL(aq)+ x2Co3 -> 2 x CLaq + H20(aq) + CO2(g)

1b)
Molar mass of HcL = 1+35.5
=36.5gmol^-1
Con of A is moldm^-3 =
Con of A of gdm^3/molar mass in gdm^3
=7.30gdm^-3/36.5gmol^-1
=0.200moldm^-3

1bii)
using CAVA/CBVB = a/b
CA = 0.200mol/dm^3
VA = 26.20cm^3
Cb = ?
VB = 25.0cm^3
a = 2mols
b = 1mol
0.200mol/dm^3 x 26.2cm^3/Cb x 25.0cm^3
= 2mols/1mol
Cb = 0.200×26.20×1/25.0×1
Cb = 5.24/25.0mol/dm^3
Cb = 0.2096mol/dm^3

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1biii)
Conc. of B in gdm-3/Conc. of B in mol/dm-3
=10.6gdm-3/0.148 gdm-3
=101.15g
=101gmol-1

1biv)
Relative atomic mass of X
2x+12+17.8=101
2x=101-29.8
2x=71.2
x=35.6



2ai)
INFERENCE:
Sample X is a soluble salt

2aii)
OBSERVATION:
A gas is evolved. The gas turns red moist litmus blue.
It forms white fumed when NaOH solution was added was added

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INFERENCE:
Alkaline gas

2aiii)
INFERENCE:
CO3 gas is CO3^2-

2aiv)
INFERENCE:
The solution is alkaline

2av)
(NH4)2CO3(aq)+2NaOH(aq) >> Na2CO3(aq)+2NH3+2H2O(g)

2bi)
REAGENTS: Adition of KSCN Solution
(Fe2+): Pale-colouration
(Fe3+) Blood red colouration
2bii)
REAGENT: Addition of NaOH solution in drop till excess
(Fe2+): Dirty green gelatineous precipitaye which is insolube in excess NaOH.
(Fe3+): Reddish brown gelatineous precipitate which is insolube in excess NaOH.
2biii)
REAGENT: Addition of K2Fe(CN) solution
(Fe2+): It forms a dark blue precipitate
(Fe3+): A deep red colouration

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3a)
i)NH4CL and AgNo3
ii)ZnCo3
iii)Fes
iv)AgNo3
v)NH4Cl

3b)
– Burrette
– Reshort Hand
– Solution/Acid
– Conical Flask
– white tile

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