2019 Waec Chemistry Questions And Answers

2019 Waec English Answers - May/June Expo

Verified Chemistry Obj
1-10: BCDCDDADDD
11-20: DADDBBACBB
21-30: DCABBDDBBB
31-40: CABDABADAD
41-50: DABBDAAABA

(1a)
(i)High temperature of 4500C or more
(ii)High pressure
(iii)Catalyst
(1b)
(i)For decoration
(ii)For protection against corrosion
(1c)
(i)Calcium oxide(CaO) is alkaline and HCl is acidic.The two react to form calcium chloride and water.
(ii)Conc. H2SO4(aq)
(1d)
Conc. HNO3(aq) reacts with a solution of FeSO4(aq) the Fe^2+ was oxidized to yellow Fe^3+ and brown NO2(g) given off
i.e 2HNO3(aq) + 2FeSO4(aq) + H2SO4 —-> Fe2(SO4)3 +2NO2(g) +2H2O

(1ei)
ZnO + H2SO4 —>ZnSO4 +H2O
ZnO +2NaOH + H2O —>Na2Zn(OH)4
(1eii)Basic oxide

(1f)
(i)They have the same number of proton
(ii)They have different mass number
(1g)
Hydrochloric acid and oxygen

(1h)
(i)H2S
(ii)SO2
(1i)
It is the average mass of atoms of the element on which one atomof carbon
It is the number of times the average mass of one atom of the element is heavier than 1/12th of the mass of one atomw carbon 12

(1j)
(i)Rate of forward reaction is equal to rate of backward reaction
(ii)It is reversible
CaCO3 → CaO + CO2
CaO + SiO2 → CaSiO3
Top of furnace
(iii) Iron (III) oxide is reduced to metallic Iron
Fe2O3 + 3CO → 2Fe + 3CO2
OR
Fe3SO4 + 4C0 –> 3 Fe + 4 CO2

===========

(2a)
(i)C10H22—–>(cracking)—->C6H14 + C4H8
P is C4H8
(ii)
H H H H
| | | |
H-C=C-C-C-H
| |
H H

H CH3 H
| | |
H-C= C- C-H
|
H
(iii)
(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

(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
(2c)
(i)
NaH-Ionic
H2-Covalent
H2S-Covalent
NH4Cl-Vanderwaals
(ii)
NaH-Soluble(dissolves)
H2-Insoluble
H2S-Moderately soluble
NH4Cl-Soluble
(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

=========
5(a) (i) – filling of weather balloons
– manufacture of plastics
– manufacture of ammonia by the Haber process
– manufacture of methanol
– oil refinery process / hydrocracking
– used in fuel cells
– manufacture of margarine
– in oxy-hydrogen flame (for welding and cutting metals}
– as reducing agent in production of metals e.g. Cu and Pb from their oxides
– conversion of coal to crude oil
– (liquid) hydrogen is used as rocket fuel / gaseous fuel
(ii) I. – temporary hardness of water
II. – scales / furring of kettles / pipes cause blockage leading to power wastage
– soap is wasted / not suitable for laundry
– not suitable for use in tanning, textiles and paper production

5(b) (i) at high temperatures oxygen gas produced at the anode reacts with the
graphite electrodes to form carbon (IV) oxide

(ii) I. CaO + H2O → Ca(OH)2
II. – used to treat acidic soil
– used to make mortar/plasters/cement/hold bricks
– in manufacture of glass
– purification of water/removing hardness of water
– manufacture of white wash
– to test for CO2
– production of bleaching powder
– to recover / produce ammonia from ammonium chloride/ used in solvay process

5(c) (i) Is the alkaline hydrolysis of fats/oils to produce soap ( and propane- 1,2,3 triol)
OR
The process in which fat or oil is boiled with alkali to produce soap (and propane -1, 2, 3-triol)

(ii) oil / fat and alkali (sodium hydroxide / potassium hydroxide)

(iii) propane-1,2,3-triol
Bottom of furnace

5(d) (i) The O2 in the hot air combines with carbon (Coke) to produce carbon (IV)
Oxide which is reduced to carbon (II) oxide.
C + O2 → CO2
CO2 + C → 2CO
Middle of furnace
(ii) The CaCO3 decomposes under great heat to form CO2 and CaO / CaCO3 decomposes to remove the impurities / SiO2
CaCO3 → CaO + CO2
CaO + SiO2 → CaSiO3
Top of furnace
(iii) Iron (III) oxide is reduced to metallic Iron
Fe2O3 + 3CO → 2Fe + 3CO2
OR
Fe3SO4 + 4C0 –> 3 Fe + 4 CO2

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