2021 WAEC GCE Chemistry (Essay & OBJ) Answers [16th December]

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WAEC GCE AUGUST/SEPTEMBER 2021 FREE CHEMISTRY (CHEM) QUESTION AND ANSWER ROOM [PRIVATE CANDIDATES]

Thursday, 16th December, 2021
Chemistry 2 (Essay) – 9:30am – 11:30am
Chemistry 1 (Objective) – 11:30am – 12:30pm
Chemistry 3 (Alternative to Practical Work) –2:00pm – 3:30 pm

A. 2021 WAEC GCE CHEMISTRY ESSAY (THEORY) ANSWERS | 16TH DECEMBER, 2021

(1a)
Sodium oxides firms an alkaline solution because it is a basic oxide which when dissolve in water will produce an alkaline

(1b)
Hygroscopic can be defined as a phenomenon in which a substance absorbs moisture from the atmosphere but does not dissolve in it and remain sticky

(1c)
Since, Mass/m.m = No. of atoms/NA
Mass/12 = 1/6.02×10²³
Mass = 12/6.02×10²³
Mass = 1.99×10²³

(1d)
CH3CH = CHCH3
This compound exhibit gases isomerism because it can rotate a plane polarised light

(1ei)
Hund's rule of maximum multiplicity states that electrons are filled singly in a sub-shells of degenerated orbital before pairing

(1eii)
--> 1s²2s²2px²2py¹2pz¹
Or use image;

(1f)
(i) Reduction reaction
(ii) LiAlH4

(1g)
When water is added to the mixture, the ethanol dissolves while the pentane can then be separated after the pentane has dissolved in water through distillation process.

(1h)
This is because the colour of the K2Cr2O7 changes from orange to green and also oxidation and reduction takes place

(1i)
This states that the rate of diffusion of a gas is inversely proportional to the square root of their vapour density provided other factors remain constant

(1j)
This is as result of their incompletely filled d-orbitals

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(2a)
(i) C17H36
(ii) C17H36
(iii) C2H2
(iv) CH3COOH and C3H7OH
(v) C2H2

(2b)
5.24/2.56 * 120+18x/120

2.56(120+18x) = 120*5.24

46.08x = 307.2 + 628.8

46.08x/46.08 = 936/46.08
x = 20

(2ci)
HF > H2O > CH4 > NH3

(2cii)
Moving from HF to NH3, their pH values increases which leads to decrease in acidity

(2ciii)
H2C = CHCl > CH3CH >H2C-CH

(2civ)
Heating a metallic surface made of zinc releases zinc fumes which is toxic and it can contaminate the food

(2di)
Pressure

(2dii)
This is because as the volume increases, the average kinetic energy is affected which leads to a decrease in pressure

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(3ai)
(i) The position of the ions in the electrochemical series
(ii) The concentration of the ions in the electrolyte
(iii) The nature of the electrode

(3aii)
Both electrodes are platinum foils

(3aiii)
At the cathode, H+ which are the only cations present, migrate to the cathode when they acquire an electron to form neutral hydrogen atoms which combine to produce diatomic gases hydrogen.
At the anode both SO4²- and OH- migrate where OH- are preferentially discharged. Gases oxygen is produced.

(3aiv)
At the cathode: 2H⁺ + 2e⁻ - - > H₂
At the anode: 4OH⁻ - -> O₂ + 2H₂O + 4e-

(3bi)
SO₂

(3bii)
(i) Reducing agent is Fe²⁺
(ii) It reduced the manganate ion from +7 to +2

(3ci)
The main role of limestone in the extraction of iron is to decompose in a hot furnace and form calcium oxide. Iron is extracted from its ore, haematite, in a blast furnace. The ore is fed into the top of the furnace along with coke and limestone. The limestone decomposes in the hot furnace, forming calcium oxide. This reacts with the sandy impurities silicon dioxide to form a slag.

(3cii)
Vanadium(v)oxide

(3ciii)
(i) Calcium oxide during decomposition
(ii) Calcium trioxosodicate during slagging.

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(5)


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B. 2021 WAEC GCE CHEMISTRY OBJECTIVES (OBJ) ANSWERS | 16TH DECEMBER, 2021

1-10: DBDDACABCB
11-20: ABDBACDABB
21-30: BDAAABBCDB
31-40: BDEDCADBBB
41-50: CCAABDCBDB


C. 2021 WAEC GCE CHEMISTRY PRACTICAL ANSWERS | 16TH DECEMBER, 2021

(1)



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(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





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(3)


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