VERIFIED CHEMISTRY PRACTICAL WAEC -{exambond} ~ Realight

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CHEMISTRY PRACTICAL LOADING............
We advice u use d solutions given on image format for better understanding.

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2020 WAEC-CHEMISTRY-PRACTICAL ANSWERS
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(1a)
In a tabular form

Burette Reading|1st reading|2nd reading|3rd reading
Final |15.25|0.00|45.79|
Initial|0.00||15.25|30.53|
Volume of acid used |15.25|15.28|15.26

Average volume of acid used = 15.25 + 15.26/2
= 15.255cm³
=15.26cm³

(1bi)
Given: Mass of conc of A = 5g/500cm³ = 5g/0.5dm³
Ca = 10g/dm³

A is HNO3
Therefore; Molar mass = 1+14+(16×3)
= 15+48
=63g/mol

Molarity of A = gram conc/molar mass
Ca = 10/63 = 0.1587mol/dm³

(1bii)
Using CaVa/CbVb = nA/nB
With reacting equation:
HNO3 +NaOH-->NaNO3 + H2O
nA = 1, nB = 1
0.1587×15.26/Cb×25.00 = 1/1
25Cb = 0.1587×15.26
CB = 0.1587×15.26/25
CB = 0.09687mol/dm³

(1biii)
B is NaOH
Molar mass = 23+16+1
=40g/mol
Conc of B in g/dm³ = molarity×molar mass
=0.09687×40
=3.8748g/dm³

(1biv)
No of moles present in 250cm³ of NaOH is
= molar conc. × volume
= 0.09687 × 250/1000
= 0.0242 moles

Mole ratio of NaOH and NaNO3 is 1:1
No of moles of NaNO3 which reacted is 0.0242
Mass of NaNO3 formed = molar mass × no of moles
= 85 × 0.0242
=2.057grams
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(2a)

TEST
C + burning splint

OBSERVATION
Sample C bursts into flame
It burns with non-smoking blue flame, without soot.
Colourless gas that turns wet with blue litmus paper faint red and turns lime water milky is present

INFERENCE
C is volatile and flammable. The gas is CO2 from combustion of a saturated organic compound.

(2bi)
TEST
C + distilled water + Shake

OBSERVATION
Clear or colourless solution is observed

INFERENCE
C is miscible with water

(2bii)
TEST
C + Acidified K2Cr2O7

OBSERVATION
Orange color of K2Cr2O7 Solution turns pale green and eventually pale blue on cooling

INFERENCE
C is a reducing agent

(2c)
TEST
D + C + 10% NaOH + Shake

OBSERVATION
D dissolve slowly in C and produces reddish brown solution

Reddish brown solution turns yellow precipitate. The precipitate has an antiseptic odour

INFERENCE
D is soluble in organic solvents

Ethanol, ethanal or a secondary alkanol is present

(2d)
Compound belongs to the class of secondary alkanol
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(3)
Typing.....

*3ai

*3bi(.)*

Phenolphtalein is chosen because it changes color in a pH range between 8.3 – 10. It will appear pink in basic solutions and clear in acidic solutions. ..

*3c(i)*
When exposed to light, silver chloride decomposes into gray metallic silver and chlorine. The light sensitivity of the silver chloride and other silver halides, such as silver bromide and silver iodide, forms the basis of the photographic process.

*3cii*
The ammonia combines with silver ions to produce a complex ion called the diamminesilver(I) ion, [Ag(NH3)2]+. This is a reversible reaction, but the complex is very stable, and the position of equilibrium lies well to the right.

*3d*
Pure copper(II) sulfate is white. It is also known as anhydrous copper(II) sulfate because it has no water in it. When water is present in a sample of copper(II) sulfate it turns blue. ... This colour change can be used to detect the presence of water (or water vapour).

No2

Or use this no2

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