2019 Waec Chemistry Obj and Theory Answers

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1-10 BCCADADACA
11-20 DDCACCDCBA
21-30 DCAABDBBAA
31-40 BACBDCDBCB
41-50 BDCCCCBDDD

(1a)
-High temperature is required
-High pressure
-The presence of Catalyst

(1b)
(i) To avoid corrosion
(ii) To avoid rusting

(1ci)
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.

(1cii)
Concentrated H2SO4(aq)

(1d)
Conc HNO#(aq) reacts with a solution of FeSO4(aq). The Fe2+ was oxidised to yellow Fe3+ and brown NO2(g) was given off.
ie 2HNO3(aq) + 2FeSO4(aq) + H2SO4 -> Fe2(SO4)3 + 2NO2(g) + 2H2O

(1ei)
(I) ZnO(s) + H2SO4(aq) —> ZnSO4(aq) + H2O(l)
(II) ZnO(s) + NaOH(aq) —> Na2ZnO2(s) + H2O(l)

(1eii)
(III) Amphoteric property

(1f)
(i) They have the same number of atoms
(ii) They have different neutron number which makes their mass number to differ

(1g)
HclO – Oxochlorate(i)acid and Hcl

(1hi)
H2S is undergoing oxidation to S(s)

(1hii)
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

(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-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

(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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