2019 Waec Chemistry Answers

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1-10   BCCADADACA
11-20 DDCACCDCBA
21-30 DCAABDBBAA
31-40 BACBDCDBCB
41-50 BDCCCCBDDD
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THEORY=======
(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 atomiv masses of all nucleids are measured. It is used to ascertain mole of a substance as the amount of substance which contains as many elementry entities as there are atoms in 12 grams of carbon-12.

(1j)
(i) The concentration of thereactants and products are equal
(ii) The rate of the forward reaction is same as rate of the backward reaction
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Question 2.

(2ai)
C10H22—–>(cracking)—->C6H14 + C4H8
P is C4H8

(2aii)
H H H H
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H-C=C-C-C-H
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H H

H CH3 H
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H-C= C- C-H
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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-Vanderwaals

(2cii)
NaH-Soluble(dissolves)
H2-Insoluble
H2S-Moderately soluble
NH4Cl-Soluble

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

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Question 3.

3ai)EquationNH3+NACL(AQ)— 2NACL

3aii)

In the first, ammonia bubbles up through the brine and is absorbed by it. In the second, carbon dioxide bubbles up through the ammoniated brine, and sodium bicarbonate (baking soda) precipitates out of the solution. Note that, in a basic solution, NaHCO3 is less water-soluble than sodium chloride.

Equation
NaHCO3 — CL+03

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Question 4.

4a

Gold extraction refers to the processes required to extract gold from its ores. This may require a combination of comminution, mineral processing, hydrometallurgical, and pyrometallurgical processes to be performed on the ore.Gold mining from alluvium ores was once achieved by techniques associated with placer mining such as simple gold panning and sluicing, resulting in direct recovery of small gold nuggets and flakes. Placer mining techniques since the mid to late 20th century have generally only been the practice of artisan miners. Hydraulic mining was used widely in the Californian gold rush, and involved breaking down alluvial deposits with high-pressure jets of water. Hard rock ores have formed the basis of the majority of commercial gold recovery operations since the middle of the 20th century where open pit and or sub-surface mining techniques are used.

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Question 5.

(5ai)
DRAW THE DIAGRAM

(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)

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