Waec 2019 Chemistry Obj And Essay Answers – May/June Expo Runs

Chemistry OBJ:
1DAABADACBD
11AABCACDADD
21CCABBDDBAA
31AABDBCDBCB
41BACBCCBDDD



(5ai)
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(5aii)
(i)It is used in the sterilization of water for domestic and industrial use and in the treatment of sewage
(ii)It is used as a bleaching agent for cotton linen and wood-pulp

(5b)
Preparation of hydrogen from water gas:
This is called Bosch process: In this process large quantities of hydrogen are produced from cheap raw materials namely water and coke when steam is passed over red hot coke (carbon) at about 1200C, a mixture of carbon(II) oxide and hydrogen ion and water gas is produced .Excess steam is then mixed with the water gas and passed over a catalyst iron(III)oxide at 450C.As a result the carbon(II)oxide in the water gas is converted by CO2 with a further yield of hydrogen
Endothermic reaction
H2O(g) + C(s)—> CO(g)

(5ci)
The chief ore of aluminium is bauxite
(5cii)
The ore of aluminium is purified by electrolysis to remove the impurities present
(5ciii)
Carbon or platinum electrodes
(5civ)
Cryolite is added to remove the impurities present

(5d)
Coal, coal tar, ammoniacal liquor



(4)
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(3ai)
Limestone is heated to generate CO2 for the reaction: CaCO3(aq) -> CaO(s) + CO2(g)
(3aii)
Ammonia is used to make brine
NH3(aq) + CO2(g) + H2O(l) -> NH4HCO3(aq)
NH4HCO3(aq) + NaCl(aq) -> NaHCO3(s) + NH4Cl(aq)

(3bi)
zymase
C6H12O6(aq) ——> 2C2H5OH(aq) + 2CO2(g)
(3bii)
On fermenting, the CO2 released, mounts pressure in the bottle and it scatters

(3ci)
Cu, Fe, Na, K
————->
Increasing reactivity
(3cii)
Sodium(N)
(3ciii)
Cu and Fe

(3di)
A redox reaction is an oxidation-reduction reaction, both occuring at the same time
(3dii)
I – Redox
II – not Redox
III- not redox
IV – not Redox
v – Redox
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(2ai)
C10H22—–>(cracking)—->C6H14 + C4H8
P is C4H8
(2aii)
H H H H
| | | |
H-C=C-C-C-H
| |
H H

H CH3 H
| | |
H-C= C- C-H
|
H
(2aiii)
P would be polymerized because it contain double bond

(2b)
Hundi’s rule: Electrons occupy each orbital singly first before pairing takes place in a degenerated orbital
Aufbau’s principle: Electrons enter into orbitals in order of increasing energy

(2ci)
– NaH —> ionic
– H2 –> Covalent
– H2S –> Covalent
– NH4Cl — Vander waals
(2cii)
– NaH —> soluble (dissolve)
– H2 –> Insoluble
– H2S –> Moderately soluble
– NH4Cl — soluble
(2ciii)
– H2S(g) + H2O(l) —> H3O^+(aq) + HS(aq)
– HS(aq) + H2O(l) —> H3O^+(aq) + S^2-(aq)

(2d)
(i)Number of unpaired electrons=zero
(ii)J would be a good reducing agent
(iii)It is found in group 2. It is a metal. Metals are good reducing agent

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(1a)
– High temperature of 4500degree(c) or more
– High pressure
– Catalyst

(1b)
– For decoration
– For protection

(1c)
Calcium oxide (Cao) is alkaline and Hcl is acidic. The two react to form calcium chloride and water; instead of dry Hcl after that, it will end up with wet calcium chloride

(1d)
This is an oxidation reaction. The acid oxidizes the iron (II) sulphate to iron (III). The baron gas evolved is Nitrogen (IV) oxide

(1ei)
(i) Zinc oxide with H2SO4
ZnO(s) + H2SO4 —> ZnSO4(aq) + H2O(l)
(ii) Zinc oxide with sodium hydroxide solutions
ZnO(s) + 2NaOH(aq) —> Na2ZnO(aq) + H2O(l)
(1eii)
Amphoteric property

(1f)
(i) Have the same atomic number
(ii) Have different mass numbers

(1g)
– Hcl
-O2

(1h)
(i) H2S
(ii) SO2

(1i)
Carbon-12 scale is the standard from which atomic masses of all nuclei’s are measured. It is used to ascertain one mole of a substance as the amount of substance which contains as many elementary entities as there are atoms in 12grams of carbon-12

(1j)
– The concentration of the resistants and products are equal
– The rate of the forward reaction is same as the rate of the backward reaction



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