All Exams Runz

Thursday, 3rd September 2020 Government 9:30 am – 11:30am

MAKE PAYMENT BELOW AND GET IT !!!
WhatsApp N500
(Full Answers Comes Direct To Your whatsApp As Message)
SEND: MTN CARDS,
SUBJECT NAME AND PHONE NUMBER TO: +2349029133233 (WHATSAPP ONLY)
NOTE: NO CALLS, ONLY MESSAGE (WHATSAPP)
All Messages to the above number will be attended to.
Payment is just MTN CARD ONLY Immediately you make payment inbox your whatsapp number to +2349029133233 and you will be added to a WhatsApp group automatically

Wishes you Best of Luck

All Exams Runz Send a message to learn more

CHEMISTRY OBJ
1-10: CACDBDADAD
11-20: AADCDABBCD
21-30: BACBCCBCAC
31-40: CBACBCDBAD
41-50: DBBDCBCCCB

==> WAEC 2020 CHEMISTRY THEORY ANSWERS
==============================
===========
(1ai)
Faraday's first law of electrolysis states that the mass(m) of an element discharged during electrolysis is directly proportional to the quantity of electricity(Q) passing through it.
(1aii)
(i) Strong electrolytes conduct large currents while Weak electrolytes do not conduct current readily.
(ii) Strong electrolytes ionize completely while weak electrolytes ionize only slightly.
(1b)
Ethyne burns in air to give a smoky and luminous flame (complete combustion)
(1ci)
If an organic compound contains carbon atoms joined by double or triple covalent bonds. The compound is said to be an unsaturated hydrocarbon.
1cii)
CH3COOH(aq) + CH3OH(aq) CH3COOCH3(l) + H2O(l)
(1ciii)
Methyl ethanoate
(1d)
By removing the main product continuously
(1e)
Number of moles of Zn dust = Mass/molars mass = 3.75/65 =0.0077
Reacting mole ratio of Zn to H2 is 1:1
:’ No of moles of H2 produced =0.0677 moles
1 mole = 6.02x10²³ molecules
0.0577moles of hydrogen produces
=6.02x10²³ x0.0577
=0.347x10²³ molecules
Or 3.47x10²² molecules
(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
(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: 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
==============================
====== =
(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
(5ai)
(i) Ammonia (NH3)
(ii) Hydrogen chloride gas(HCl)
==============================
====== =
(4ai)
I
(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)
==============================
====== =
(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.