Waec gce chemistry answers 2021

Here is the waec gce chemistry answers 2021, we will post the complete answers here.

Chemistry answers

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Completed

(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; [img]https://i.imgur.com/zLnYsDh.jpg[/img]

(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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(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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(2iv)

Galvanized metal containers are not considered safe for cooking. The galvanizing process creates a coating to the metal that prohibits rust. This coating contains zinc, which can be toxic when consumed.

(3ai)

(i) Position of the ions in the electrochemical series

(ii) Concentration of ions

(iii) Nature of electrode

(iv) Concentration of the ions in the electrolyte

(v) Relationship between the position of ions in the electrochemical series

(3aii)

Platinum electrodes

(3aiii)

Dilute sulfuric acid contains water. The ions present in this mixture are H+ and OH- from the water and H+ and SO₄²⁻ from the sulfuric acid. The H+ ions are attracted to the cathode and the two negative ions are attracted to the anode but it is the OH- ion that loses electrons.

(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

(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

(5a)

3H₂(g) + N₂(g) <—> 2NH₃(g) -∆H

(i) Decreasing the temperature will favour the forward reaction and give a high yield of ammonia

(ii) Increasing the pressure will also favour the forward reaction and give a high yield at ammonia

(5bi)

Bauxite is preferred because other sources contain high Silicon content

(5bii)

(i) Iron(iii)oxide

(ii) trioxosilicates(iv)

(5biii)

NaOH is used to purify the ore

(5biv)

Aluminum is very reactive and cannot be easily reduced from its oxide

(5ci)

Water gas is prepared by passing steam over white hot coke at 1000°c

C(s) + H₃O(g) – -> Co(g) + H₂(g)

(5cii)

Because of the acidic character of aqueous Fe³⁺ ion, Iron(iii) hydroxide will be formed instead of Iron(iii) carbonate due to the displacement at CO₂

(5di)

Sodium darts about and melts into a silvery ball

(5dii)

2Na(s) + 2H₂O(l) —> 2NaOH(aq) + H₂(g)

(5diii)

3.0g of sodium produces 3.0/23 moles

Number of moles of gas produce

= 1/2 x 3/23

= 3/46moles

Volume of gas at S.t.p produced

= 22.4 x 3/46 dm³

= 1.46dm³

(4ai)

This is a type of hard water that can be removed by boiling

(4aii)

Ca²+(aq) + Na2CO3 (aq) –> CuCO3(s) + 2Na+(aq)

(4aiii)

TABULATE

(i)TEST: Sample + conc. H2SO4 + heat

OBSERVATION: Brown fumes of NO2 evolved

(ii)TEST: Sample + copper + Conc. H2SO4 and

OBSERVATION: Reddish brown fume of NO2

(4bi)

(i) It is used as ingredient in antacid

(ii) It is used as reducing agent

(iii) It is used as food supplement to build string bones

(4bii)

(i) Coal tar

(ii) Coal gas

(4biii)

These are chemical that are produced in a little quantity in the industry

(4ci)

(i)In an unlimited supply of air, Carbon (iv) oxide is formed (CO2)

(ii) in a limited supply of air , Carbon(ii) oxide is formed

(4cii)

C(s) + 02(g) —> CO2(g)

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