Waec GCE Chemistry Practical Answer 2021

CHEMISTRY PRACTICAL INSTRUCTIONS

ANSWER ALL QUESTIONS

 

NUMBER 1

NUMBER 2

NUMBER 3

 

COMPLETED

 

(1ai)

TABULATE

 

Burette reading(cm³); 1 | 2 | 3

Final reading; 21.50 | 22.40 | 32.20

Initial reading; 2.50 | 4.00 | 13.60

Volume of Acid used; 19.00 | 18.40 | 18.60

 

(1aii)

Average volume of acid used

= 18.40 +18.60/2

= 18.50cm³

 

(1bi)

Concentration of B in mol/dm²

Using;

CAVA/CBVB= nA/nB

(0.086×18.50) /CBx20.00 = 2/1

CB = 0.086×18.50/2×20.00

CB = 0.039775mol/dm³

 

(1bii)

Number of moles of I₂

= Volume x Molarity

= 1 x 0.06

= 0.06moles

 

(1biii)

gram concentration of hydrocarbon

= 4.8/1 = 4.8g/dm³

Molarity = gram conc./Molar mass

= 4.8/80

= 0.06mol/dm³

Molar concentration = 0.06mol/dm³

===================================

(2i)

TABULATE

 

-TEST-

Sample(aq) + NH₃(aq) in drops then in excess

 

-OBSERVATION-

Blue precipitate

Precipitate dissolves in excess

 

-INFERENCE-

Cu²+ Indicated

Cu²+ confirmed

 

(2ii)

-TEST-

Sample(aq) + NaOH(aq) in drops then in excess

 

-OBSERVATION-

White gelatinous precipitate

Precipitate soluble

 

-INFERENCE-

Al³+ indicated

Zn²+ confirmed

 

(2iii)

-TEST-

Sample(aq) + AgNO₃(aq) in drops then in excess

Solution(iii) + excess NH₃(aq)

 

-OBSERVATION-

White precipitate formed

Precipitate soluble in excess NH₃(aq)

 

-INFERENCE-

Cl- indicated

Cl⁻ confirmed

 

(2iv)

-TEST-

Sample(aq) + HCl(aq)

 

-OBSERVATION-

Rapid effervescence gad evolved turned lime water milky

 

-INFERENCE-

CO₃²- indicated

CO₃²⁻ confirmed

 

(2v)

-TEST-

Sample(aq) + heat

 

-OBSERVATION-

Reddish-brown gas evolved

 

-INFERENCE-

Gas is NO₂

NO₃⁻ confirmed

 

(2vi)

-TEST-

Sample(aq) + NaOH(aq) + heat

 

-OBSERVATION-

Pungent smelling gas evolved which turned moist red litmus paper blue

 

-INFERENCE-

Gas is NH₃ and NH₄⁺ indicated

NH₄⁺ confirmed

===================================

(3a)

(i) Benedict’s reagent

(ii) Lucas’ reagent

(iii) Ninhydrin test

(iv) Bromine reaction

 

(3b)

A stopper stuck in the bottle can be removed by pouring hot water on the neck of the bottle because the hot water loosens the material by weakening the inter-molecular forces in between. The bottle cap is made of a material that loosens its strength when it absorbs heat.

 

(3ci)

Equivalence point is the point in a titration where the amount of titrants added is enough to completely neutralize the analyst solution.

 

(3cii)

(i) Spatula; It is used for scraping, transferring, or applying powders and paste-like chemicals or treatments

(ii) Crucible; It is used to burn, melt or mix solid chemical compounds over a burner.

(iii) White tile; it is placed underneath a conical flask to aid with the ease of spotting the end point colour change.

 

(3ciii)

(i) This is because distilled water change the concentration of the initial solution

(ii) In order to measure the amount of solution added in or drained out

 

(3di)

(i) Ethene

(ii) Butyne

 

(3dii)

N₂, CO₂, NH₃

===================================

GOOD LUCK

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