-NECO 2015 RUNS (CHEMISTRY PRACTICAL)

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PLS IN NUMBER 2, THE TABLE HAS BEEN DRAWN SHOWING: TEST | OBSERVATION | INFERENCE.
THEN PLACE THE ANSWERS WE SENT UNDER IT’S SUITING POSITION AS DRAWN IN THE TABLE.
Goodluck!
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(1a)
Titre value:

Under 1:
20.70, 0.00, 20.70

Under2:
20.70, 0.00, 20.70

Under3:
20.70, 0.00, 20.70

Under Initial reading:
0.00, 0.00, 20.70, 20.70

Under volume of Acid used:
20.70, 20.70, 20.70

Average value= (20.70+20.70= 20.70)/3

VA=(63.10)/3= 20.70cm^3

(1bi)
Given CA=?
CB=0.10mol^-3
VA=20.70 cm^3
VB=25.0CM^3
NA=1
NB=2
H2C2O4+ 2NAOH=> Na2C2O4+ 2H20
CAVA/CBVB= NA/NB
(CA*20.70)/0.10 *25.00cm^3= 1/2
CA= (1*0.10*25.0)/2*20.70
CA2.50/41.40
=0.603mol dm^-3

(1bii)
CA=mass concentration/molar mass
H2C2O4=((2*4)+(2*c)+(4*0))gmol
((2*1)+(2*2)+(4*10))g/mol
2+24+48g/mol
=72g/mol
0.0603= mass contration/72
=4.348g/dm^3

(1biii)
mass of pure= 4.35gdm^-3
mass of impure=6.30g/dm^-3
% purity= mass of pure/ mass of impure * 100%
=4.35/6.30 * 100%
=4.35/6.30 %
% purity= 69.01%

(1biv)
methyl orange is not used because it is a titration between weak acid and strong base, the end point will not coincide with the PH which the indicator exhibits of colour change

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(2ai)
OBservation: salt C dissolves in distilled water

inference: Salt C is a soluble salt

(2bi)

observation:

Rusty brown precipitate is formed in excess

interference:

Fe(3+) is present

(2bii)

OBSERVATION: formation of blood-red precipitate

Inference: Fe(3+) is confirmed

(2ci)

Observation: formation of white precipitate which dissolves on heating

Inference: SO3(2-), SO4(2-) are likely to present

(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.

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(3ai)
using lime water

(3aii) by determining its boiling point and melting point

(3aiii)by direct evaporation

(3aiv)by sieving

(3bi)addition of water, to be followed by filtration and then crystallization

(3bii)in evaporation, the salt are always stable to heat.

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COMPLETED
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