WAAEC 2020/2021 Chemistry Essay & Objective Question and Answers Now Available

WAAEC 2020/2021 CHEMISTRY ESSAY & OBJECTIVE QUESTION and ANSWERS NOW AVAILABLE

CHEMISTRY OBJ

01-10: CACCBDADAC

11-20: ACDCDABADA

21-30: BABACCBAAC

31-40: CBACBCDBAA

41-50: DBADCBBBCB

COMPLETED


(1ai)

Faraday’s first law of electrolysis states that the amount of element deposited at the electrodes is directly proportional to the quantity of electricity applied in the electrolysis.

(1aii)

Strong electrolytes ionize completely (100%), while weak electrolytes ionize only partially.

(1b)

Properties of Ethyne

(Pick one)

(i) Ethyne is a colorless gas with a sweet smell when pure.

(ii) It is slightly less dense than air

(iii) It is almost insoluble in water.

(iv) It burns with a sooty flame due to high proportion of unburnt carbon.

(1c)

Unsaturated hydrocarbons are hydrocarbons that have double or triple covalent bonds between adjacent carbon atoms.

(1cii)

CH3COOH + CH3OH–>CH3COOCH3 + H2O

(1ciii)

methly ethanoate

(1d)

Addition of catalysis I;e it catalyzed by a high concentration of hydrogen ion

(1e)

Mzn = 3.75g

Mzn = 65.0g/mol

n= m/M=3.75/65.0

n=0.0577mole

nH² =0.0577mole because the mole ratio is the same

np =n*L

np=0.0577*6.02*10^23

np=3.47*10^22 moles

(1f)

(Pick one)

(i) Increase in Average temperature

(ii) Far-reaching and long lasting Changes to the natural Environment.

(1gi)

Reaction C

(1gii)

Zinc (From +2 to +4)

 

(1hi)

(i) Each spectral line is caused by an electron

(ii) Electrons can exist only in circular orbits of definite quantum energy.

 

(1hii)

It could not account for the spectrum at more complicated atoms

 

(1i)

(i) Temperature of the reacting system.

(ii) Pressure of the reacting system.

(iii) concentration of the reacting system.

 

(1j)

(i) Both liberate carbon(iv) oxide

(ii) One produce a chloride salt , the other produce an ethanoate salt.

+++++++++++++++++++++++++++++++++

SECTION B

 

(2ai)

isomers

 

(2aii)

A = trans 1,2 dichloroethane

 

B=Cis 1,2 dichloroethane

 

2aiii) Yes.

 

(2aiv)

Because they are isomers. Isomers have same chemical properties but different physical properties.

 

(2bi)

(i) Destroying gaseous emissions.

(ii) Boiling is the rapid vaporization of a liquid

 

(2bii)

WHEN NACL IS ADDED: The more salt (or any solute) added to water, the more you raise the boiling point. Reduction of atmospheric pressure lowering the atmospheric pressure will lower the boiling point of the liquid.

 

(2c)

A saturated solution contains the maximum amount of solute that will dissolve at that temperature. Any further addition of solute will result in undissolved solid on the bottom of the container. An unsaturated solution contains less than the maximum amount of solute that can be dissolved at that temperature.

 

(2cii)

Add solute to a liquid until no more will dissolve. Solubility often increases with temperature, so you may be able to get more solute into a hot solvent than you would if Increase in pressure

 

(2cii)

Temperature and Pressure

 

(★) Temperature affects the solubility of both solids and gases,

 

(★) Pressure only affects the solubility of gases

+++++++++++++++++++++++++++++++++

(3ai)

Draw the diagram

 

(3aii)

I. Activation Energy = (210 – 100)KJ = 110K

II. Hp – HR = ΔH

54 – 100 = -46KJ

 

(3aiii)

Q2(g) + R2(g) –> 2QR(g)

 

(3aiv)

Exothermic reaction.

 

(3av)

The heat content of the reactant is higher than that of the product.

 

(3bi)

E7 – 1s² 2S² 2P³

F9 – 1s² 2S² 2P⁵

G12 – 1S² 2S² 2P⁶ 3S²

H13 – 1S² 2s² 2P⁶ 3S² 3P¹

 

(3bii)

I. G and H

II. H

III. F

IV. GF2

 

(3ci)

Isotopy is the existence of an element in more than one physical form with the same atomic number but different atomic masses.

 

(3d)

(i) Atoms

(ii) Molecules

(iii) ions

 

5a) ammonia,

hydrogen chloride

sulfur dioxide (Choose any 2)

5aii) The aim of the fountain experiment is to prove that HCI is highly soluble in water.

 

5aiii) The experiment consists of introducing water through an inlet to a container filled with ammonia gas…. Ammonia dissolves into the water and the pressure in the container drops. As a result, more water is forced into the container from another inlet creating a fountain effect

 

5b) Fumman Chemicals

-Chellerams PLC

-Cormart Nigeria Limited

(Choose any 2)

 

5bii) The magnitude of the emitted to the air dusts and gases, liquid and solid wastes disposal produced by chemical industry is presented

-.. Some hazardous agents, occurring in the work environment, morbidity and sickness absenteeism rates, noted among employees in chemical industry, are considered.

 

5ci)

Coke

coal gas

gas carbon

coal tar ammonia liquor

*Choose any 3)

5cii) COKE=>It is used to reduce iron oxide to produce iron.

 

Coal gas=>is used in lighting

 

Coal tar=>It may be applied to the affected area to treat psoriasis and seborrheic dermatitis (dandruff).

 

(CHOOSE ANY 2).

 

5di)

– calcium

-magnesium

 

5dii)ion-exchange resin

-reverse osmosis.

– precipitation methods

(Choose any 2)

 

5diii)

Calcium ions in the water are good for children’s teeth and bones.

-Limescale (a hard crust) forms inside kettles.

-This wastes energy whenever you boil a kettle. It helps to reduce heart disease.

 

Choose any 2

SECTION B

 

(2ai)

isomers

 

(2aii)

A = trans 1,2 dichloroethane

 

B=Cis 1,2 dichloroethane

 

2aiii) Yes.

 

(2aiv)

Because they are isomers. Isomers have same chemical properties but different physical properties.

 

(2bi)

(i) Destroying gaseous emissions.

(ii) Boiling is the rapid vaporization of a liquid

 

(2bii)

WHEN NACL IS ADDED: The more salt (or any solute) added to water, the more you raise the boiling point. Reduction of atmospheric pressure lowering the atmospheric pressure will lower the boiling point of the liquid.

 

(2c)

A saturated solution contains the maximum amount of solute that will dissolve at that temperature. Any further addition of solute will result in undissolved solid on the bottom of the container. An unsaturated solution contains less than the maximum amount of solute that can be dissolved at that temperature.

 

(2cii)

Add solute to a liquid until no more will dissolve. Solubility often increases with temperature, so you may be able to get more solute into a hot solvent than you would if Increase in pressure

 

(2cii)

TEMPERATURE: Temperature affects the solubility of both solids and gases,

 

PRESSURE: Pressure only affects the solubility of gases

 

(2di)

Mole is the amount of substance that contains as many elementary particles or entities as there are carbon atoms in 12 grammes of carbon -12 isotope

 

(2dii)

MgO(s) + 2HCl(aq) —–> MgCl2(aq) + H2O(l)

1 mole of MgO Neutralizes 2 moles of HCl

Reacting mole of HCl = 25.0 × 0.1 ÷ 1000

= 0.0025 mole.

 

Number of moles of MgO =0.0025/2

=0.00125 mole

 

But, mole =Mass/molar mass

Mass= mole × molar mass

Molar mass of MgO= 24 + 16

= 40g/mol.

Mass of MgO = 40 × 0.00125

=0.05g

 

(2e)

(i) They have high melting and boiling points.

(ii) They are hard but brittle with high tensile strength

(iii) They are good conductors of heat and electricity

(iv) They are malleable



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