WAEC 2020 CHEMISTRY PRACTICAL ANSWERS – EXPO RUNS

Nabteb Gce 2019 Official Timetable
Neco Gce Chemistry Practical Answers – Nov/Dec 2018 Expo

Kindly use your school endpoints.

(1a)
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
=15.255cm³
=15.26cm³
Or =15.27cm³

(1b)
Given; mass con of A =5g/500cm³ = 5g/0.5dn³
CA=10g/dm³
A is HNO3
Therefore molar mass =1+14+(16*3)=15+48=63g/mol¹

Molarity of A = gram con/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
0.158715.26/CB25.00=1/1
25CB=0.158715.26
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
=0.09687250/1000
=0.0242moles
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
=85
0.0242
=2.05grams
CLICK HERE FOR THE IMAGE
CLICK HERE FOR THE IMAGE



 

(2a)
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.

(2bi)
TEST: C + distilled water + shake

OBSERVATION: Clear or colorless solution is observed

INFERENCE: C is miscible with water

(2bii)
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

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

CLICK HERE FOR THE IMAGE


 

(3)
CLICK HERE FOR THE IMAGE
CLICK HERE FOR THE IMAGE

 

(3ai)
Zinc nitrate

(3aii)
2 Zn(NO 3 )2 —–>2 ZnO + 4 NO 2 + O 2

(3aiii)
It turns white when cold from it yellow colour when it was hot

(3b)
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.

(3c)
Al2(SO4)3 – turns blue litmus red

 

COMPLETED
NONI LOVES YOU ALL

COMMENTS

WORDPRESS: 2
  • comment-avatar
    Princewill 1 month ago

    Good work

  • comment-avatar

    Very good post but was not timely,you can do better to published on time


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