Neco 2015 Practical Chemistry answers

NECO 2015 Practical CHEMISTRY ANSWERS
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Rough : 30.00 , 0.00 , 30.00
Ist trial: 23.00 , 0.00 , 23.00
2nd trial: 23.10 , 0.00 , 23.10
3rd trial: 23.90 , 0.00 , 23.90
1) Average titre value = 23.00 +
23.10 + 23.90 / 3
= 23.00cm3
II) Vol of A used H2C2O4 = (1×2) +
(1×2) + (16×4)
= 90g/mol
CaVa/CbVb x Ra/Rb
Ca = 0.10 x 23 x 1 / 23 x 2
= 0.0543mol/dm3
III) Percentage Purity of A
Molarity = Mass conc / molar mass
Molar mass of A = 90g/mol
= 0.0543 = Mass conc/ 90gmol
Mass conc = 0.0543 x 90 = 4.887g/
mol
%purity = 4.887/6.3 x 100
= 77.57%
IV) Reason is that: The Reaction
between weak acid and Strong
base.
2a)
Test: Put c into a test and add about
5cm of distilled water & shake
thoroughly
Observation: soluble in Water
Inference: soluble Salt
—————————————————
2bi)
Test: Divide the filtrate into 2
portion, to the first portion and
dilute sodium hydroxide sol in
Drops & excess
Observation: Reddish Brown ppt
formed insoluble in excess Naoh
sol
Inference: Fe3+ is present in
soluble and Fe3+ is present in
excess
—————————————————
2bii)
Test: To the Second portion add
potassium thiocynate solution
Observation: Brown ppt form Reddish
Inference: Fe3+ confirmed
—————————————————
2ci)
Observation: Gas
evolved,colourless irritating smell,
turn blue litmus paper red
Inference: SO2+ gas is from So3^2-
—————————————————
(2cii)
Observation:
A pungent gas is evolved, the gas
turns moist blue litmus paper to
red and turns acidified K2Cr2O7
from orange to green colour
Inference:
an acidic gas is evolved i.e SO2 gas
is evolved from SO3(2-)
—————————————————
(2ciii)
observation: white precipitate is
formed
Inference: SO4(2-), SO3(2-) are
likely present
—————————————————
(2iV)
observation: the white precipitate
is soluble in dil HCL
Inference: SO3(2-) present.
3a) By using Activated charcoal
3aii.-the boilling melt of the water
must be at 100degree
-the water must give spit on a
paper
chromotography
-the freezing point must be 0degree
3iii) adding of sodium chloride
pilets to the solution
3iv.sieving for separating mixture
of
different solid particles
3b) Add water to the solution of
starch and glucose stir the solution
and filter the starch remains as
residue while glucose become a
filtrate
3c: Loss of water

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