WAEC-CHEMISTRY-ANSWERS
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WAEC-CHEMISTRY-ANSWERS
Chemistry-Obj.
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Use It Is Very Accurate.
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Answer only four

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(4ai)
I – Potassium tetraoxomanganate (vii)
– Hydrochloric acid
II : Concentrated tetraoxosulphate (vi) acid
III : Downward delivery

(4aii)
2KMnO4(aq) + 16HCl(aq) —> 2MnCl2(aq) + 2KCl(aq) + 8H2O(l) + 5cl2(g)

(4aiii)
3Cl2(g) + 6NnOH(aq) —-> NaClO3(g) + 5NaCl(aq) + 3H2O(l)

(4bi)
– Iron (III) oxide
– Coke
– Limestone

(4bii)
C(s) + O2(g) —-> CO2(g)
CO2(g) + C(s) —-> 2CO(g)
FeO3(s) + 3CO(g) —-> 2Fe(l) + 3CO2(g)
CaCO3(s) —> CaO(s) + CO2(g)
SiO2(g) + CaO(s) —-> CaSiO2(s)

(4biii)
Pig iron

(4biv)
The iron has a relatively low melting point because it contains impurities

(4ci)
It is not dissolves directly in water because the heat evolved during the process would cause the acid solution to boil, producing a mist of acid droplets which would spread throughout the factory

(4cii)
It is regarded as a heavy chemical because it is produced in very large quantities and used in many chemical processes

(4ciii)
I : Displacement reaction
II : As an oxidizing agent

(4d)
2C3H7OH(aq) + 2Na(s) —-> 2C3H7ONa(aq) + H2(g)
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(3ai)

(3aii)
Activation energy =(210-100)kj =110Kj
HP-HR =DH
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.

(3b)
E7 – 1s²,2s²,2p³, or K2, L5

F9 – 1s²,2s²,2p^5 or K2,L7

G12 – 1s²,2s²,2p^5,3s² or K2,L8,M2

H13 – 1s²,2s²,2p^6,3s²,3p¹ or K2,L8,M3

(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
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(5a)
(i)ammonia (NH³)
(ii)hydrogen chloride gas(HCl)

(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. In other words the water turns red.

(5bi)
(i)Petrochemical industries
(ii)Pharmaceutical industries.

(5bii)
(i)Pollution of water bodies by chemical waste
(ii)Pollution of the air
(iii)Radiation particles are released

(5ci)
(i)Coke
(ii)coal gas
(iii)Coal tar

(5cii)
(i)Coke- It is used to reduce iron oxide to produce iron.
(ii)Coal gas=>is used in lighting

(5di)
(i)calcium
(ii)magnesium

(5dii)
(i)reverse osmosis.
(ii)precipitation methods.

(5diii)
(i)Limescale (a hard crust) forms inside kettles.
(ii)This wastes energy whenever you boil a kettle. It helps to reduce heart disease.
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(2ai)
The relationship between the compounds A and B is that they have similar chemical properties

(2aii)
– A : Trans-1,2-dichloroethene
– B : Cis-1,2-dichloroethene

(2aiii)
Their chemical properties will be the same

(2aiv)
The reason is because they are geometric isomers. Geometric isomers have the same chemical properties but different physical properties.

(2bi)
(i)Temperature remains constant during boiling
(ii)There is change of state during boiling

(2bii)
(i)It increase the boiling point of water
(ii)It reduce the boiling point of water

(2biii)
(i)Boiling occurs at a specific temperature while evaporation occurs at almost all temperature.
(ii)during boiling temperature remains constant while during evaporation temperature changes

(2ci)
An unsaturated solution is one that contain less than the maximum amount of solute that can dissolve at a given temperature while saturated solution is one that contain maximum amount of solute that can be dissolved in it at that temperature

(2cii)
(i)By increasing the temperature of the solution
(ii)Increasing the amount of solute

(2ciii)
Temperature

(2di)
Mole is the amount of substance that contains as many elementary particles or entitle as there are carbon atoms in 12 Grammies of carbon – 12 isotope

(2dii)
MgO(s) + 2HCl(aq)—->MgCl²(aq)+H2O(I)
1mole of MgO neutralize 2 mole of HCl
Reacting mole of HCl = 25.0*0.1/1000=0.0025mole
No of moles of MgO =0.0025/2 =0.00125mole
But mole =mass/m. Mass , mass = mole*m. 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 point
(ii)They hard but brittle with high tensile strength
(iii)They are good conductors of heat and electricity
(iv)They are malleable
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(1ai)
Faraday’s First Law of Electrolysis states that the chemical deposition due to the flow of current through an electrolyte is directly proportional to the quantity of electricity (coulombs) passed through it.

(1aii)
Strong electrolytes ionize completely (100%), while weak electrolytes ionize only partially.

(1b)
CHEMICAL PROPERTY OF EHYNE
– COMBUSTION REACTION: Ethyne burns in air with a luminous smoky flame and hence used for lightening purpose.
2C2H2 + 5O2 —–> 4CO2 + 2H2O + heat

(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)
By removing the main product continuously.

(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)
Flooding

(1gi)
Reaction C

(1gii)
Zinc (from + 2 to + 4)

(1hi)
(i)Each spectral line is caused by one electron
(ii)Electron can exist only in circular orbit of definite quantum energy.

(1hii)
It could not account for the spectrum at note complicated atoms

(1i)
(i)Temperature of the reacting system
(ii)Pressure of the reacting system
(iii)Concentration of the reacting system

(1ji)
Both liberate carbon(iv) oxide

(1jii)
One produce a chloride salt , the other produce an ethronate salt