Waec 2020 chemistry practical answer


Burette reading (cm)³|1st reading|2na Reading|3rd reading|
Final |15.25|30.53|45.79|
Initial |0.00|15.25|30.53|
Volume of acids used |15.25|15.28|15.26
Average volume of acid used =15.25+15.26/2
Or =15.27cm³

Given; mass con of A =5g/500cm³ = 5g/0.5dn³
A is HNO3
Therefore molar mass =1+14+(16*3)=15+48=63g/mol¹

Molarity of A = gram con/molar mass

With reacting equation ; HNO³ + NaOH—NaNO3+H2O
nA=1 nB=1

B is NaOH
Molar mass
Conc of B in g/dm³=molarity * molar mass
= 0.09687*40

No of moles present in 250cm³ of NaOH is =molar conc * volume
Mole ratio of NaOH and NaNO3 is 1;1
No; of mole of NaNO3 which reacted is 0.0242
Mass of NaNO3 formed =molar mass * no; of moles

TEST: C+burning splint

OBSERVATION: Sample C burst into flame .It burns with non smoky blue flame without soot. Colorless gas that turns wet blue litmus paper faint red and turns like water milky is present.

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

TEST: C + distilled water + shake

OBSERVATION: Clear or colorless solution is observed

INFERENCE: C is miscible with water

TEST: C + Acidified K2Cr207

OBSERVATION: Orange color of K2Cr207 solution turns pale green and eventually pale blue on cooling

INFERENCE: C is a reducing agent

Compound belongs to the class of secondary alkanol

Zinc nitrate

2 Zn(NO 3 )2 —–>2 ZnO + 4 NO 2 + O 2

It turns white when cold from it yellow colour when it was hot

Pipette / measure 50.0cm3 of the stock solution into a 250
cm3 volumetric flask (containing some distilled water). Shake / swirl and add more distilled water until the mark is reached.

Al2(SO4)3 – turns blue litmus red

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