2021 WAEC MAY/JUNE CHEMISTRY Questions & Answers: 2020 WAEC MAY/JUNE CHEMISTRY ANSWERS Night before Exam

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CHEMISTRY OBJ

1 - 10: CACDBDADBB
11 - 20: AACCDABBDD
21 - 30: BBCDCBBAAC
31 - 40: CBACBCDBAD
41 - 50: DBBDCBCCCB

 

==COMPLETED==

 

Numbering corrected in NO. (1jii)

 

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

You are to Answer a total of FOUR (4) QUESTIONS. You are to answer No. 1 and any other THREE (3) Questions. We tried to answer many questions for the sake of people writing in the same school, so you can choose which one to answer and leave the rest.


 



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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=0.0577×6.02×10²³
np=3.47×10²² 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 a circular orbit of definite quantum energy.

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

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

(1j)
Both liberate carbon(iv) oxide(1jii)


(1jii)

One produces a chloride salt, the other produces an ethronate salt


2021 WAEC MAY/JUNE CHEMISTRY Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE CHEMISTRY Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
====

 

(2ai)
They are isomers

(2aii)
A - Trans 1,2 dichloroethane

B - Cis 1,2 dichloroethane

(2aiii)
Yes

(2aiv)
They contain the same functional group the single bond. The only difference is the polarity(physical property)
The Cis - polar compound while Trans-1, -di chloroethane is non polar

(2bi)
(i) The temperature remains constant during boiling
(ii) There is a change of state during boiling

(2bii)
I - It will increase the boiling point of water.
II - It will reduce the boiling point of water.

(2biii)
Boiling occurs at a specific temperature While Evaporation occurs at almost all temperatures.

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

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

(2ciii)
Temperature.

(2di)
Mole is a standard scientific unit for measuring large quantities of very small entities such as atoms, molecules, or other specified particles

(2dii)
MgO(s)+2HCl(aq) ---> MgCl(aq)+H2O(l)
From the equation of reaction; 1 mole of MgO = 2 moles of HCl
Hence n = cv/100
where c = 0.1moldm-³; v = 25.0cm³
No of mole of HCl = n = 0.1x25/1000
= 2.5 x 10-³ moles
Hence the no of moles ofMgO required = 2.5/2 x10-³
But n = m/M = reacting mass/ Molar mass ---> m = nM = 1.25x10-³ x 40
= 50 x 10-³ = 0.05g of MgO.

(2e)
(i) They are malleable
(ii) They are ductile
(iii) They are good conductors of heat and electricity





2021 WAEC MAY/JUNE CHEMISTRY Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
=====

 

(3ai)

(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

 


2021 WAEC MAY/JUNE CHEMISTRY Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 WAEC MAY/JUNE CHEMISTRY Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
===

 

(4ai)

(i) Potassium tetraoxomanganate (vii)
(ii) 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)
(i) Iron (III) oxide
(ii) Coke
(iii) 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 dissolved 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)





2021 WAEC MAY/JUNE CHEMISTRY Questions & Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
===

 

(5ai)
(i) Ammonia (NH3)
(ii) Hydrogen chloride gas(HCl)

(5aii)
To show that hydrogen chloride is extremely soluble in water.

(5aiii)
Fill a round-bottomed flask with dry hydrogen chloride through a tube A and air through another tube B. Add a few drops of water through B and close the tubes. Invert the flask into a trough of water containing blue litmus solution. The water turns red.

(5bi)
Petrochemical industries.
Pharmaceutical industries.

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

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

(5cii)
(i) Coal gas --> Importsmt gaseous fuel.
(ii) Coke --> Used as a reducing agent.

(5di)
(i) Calcium tetraoxosulphate(vi)
(ii) Calcium hydrogentrioxocarbonate(iv)

(5dii)
(i) By boiling.
(ii) Addition of caustic Soda.

(5diii)
(i) Hard water contains dissolved minerals and therefore tastes better.
(ii) The calcium salts on hard water help animals to build strong teeth and bones.

 


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Updated At: April 12th 2021, (08:04:08)

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