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PAST QUESTIONS WAEC

2020 NECO Chemistry Essay Questions and Answers For all Candidates

Neco Biology Questions
Written by Nkedugist

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  • NECO GCE Chemistry Questions Questions
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  • NECO Chemistry Questions
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  • 2020 NECO Chemistry Questions

CHEMISTRY PAPER II
Paper 2 will last for 1 hour 30min
Attempt two questions from this section

(1a)
Ammonium chloride —> sublimation
Ink —> chromatography
Iron filling —> magnetic separation

(1aii)
-Example Of physical Change
(i)change of matter
(ii)evaporation of sodium chloride

-Example of chemical change
(i)burning of firewood
(ii)rusting of iron

(1bi)
(i)they are good reducing agent
(ii)they form basic oxide
(iii)they formed electro valent bonding

(1bii)
Aluminum tetraoxosulphate(vi) is prepared by the action of hot concentrated tetraoxosulphate(vi)acid on aluminum oxide
Al2O3(s) + 3H2SO4(aq)—->Al2(SO4)3(aq)+3H2O(i)
Aluminum tetraoxosulphate(vi) is moderately soluble in water

(1ci)
Hydrogen

(1cii)
(i)it is denser than air
(ii)it is very poisonous

(1ciii)
Pb(NO3)2+H2S—->Pbs+2HNO3

(1civ)
It turn black due to the formation of black lead (II) sulphide

(1di)
Water gas contains flammable gases whereas the producer gas contains both flammable and non-flammable gases

(1dii)
(I) Diamond —> Octahedral in shape
(II) Graphite —> Hexagonal in shape

(1e)
(i) For manufacturing of ammonia and fertilizer
(ii) It is used as a refrigerant and also used to shrink metal parts
(iii) It is used in grinding substances that are too tough to grind at normal temperature

(2aii)
Avogadro’s law states that equal volumes of all gases under the same temperature and pressure contain the same number of molecules

(2aii)
Given : 2SO2(aq) + O2(g) –> 2SO3(aq)

The volume of oxygen, O2 required = 1/2*7.50dm³
=3.75dm³

No of moles required = 3.75/22.4moles
=0.1674moles

No of oxygen molecules required = 0.1674×6.02×10^23
=1.008×10^23molecules

(2bi)
(I) NaCl —–> Valency of chlorine is 1
(II) NaO2 —–> Valency of oxygen is 2
(III) Na3N ——> Valency of Nitrogen is 3

(2bii)
(i)Formation of black soap
(ii)Formation of glycerol
(iii)It helps in the precipitation of large biomolecules such as protein

(2ci)
(i)Na2O
(ii)MgO
(iii)CaO

(2cii)
Because they react with water to form acids

(2ciii)
– Reaction with sulphur
S(s) + O2(g) —> SO2(g)

– Reaction with metals
4Na(s) + O2(g) —-> 2NaO(s)

(2di)
Ion is any atom or group of atoms which possess an electric charge

(2dii)
TABULATE PLS
ION : H^+, F^-, N^3+

NUMBER OF PROTONS: 1,9,13

NUMBER OF NEUTRONS : 0, 10, 14

NUMBER OF ELECTRONS : 0, 10, 10

(2ei)
Monosaccharide are simple six carbon sugar having the formula C6H12O6 eg glucose and it’s isomers are fructose and galactose, both obtainable from fruits and honey

(2eii)
(i)fructose
(ii)galactose

3b)
In other words the oil is stained red. This is a specific test for fats if suden (iii) is added to fats a distinct red colouration is observed
3c)
Given 2502+02+2H20—>2H2SO4
1mole produce 2mole
1.3mole produce 3mole
moles of H2SO4=3mole
molar mass of H2SO4=(1+2)+32+(4*16)
=2+32+64 = 98gmol-^1
mole=mass/molar mass
mass and H2SO4=Mole*molar mass
=3*98 =294g
3di) DH2
4ai) Thermal cracking
4aii) C4H8
4aiii)
(I) H H. H
| | |
H-C-C-C=C
| | | |
H H H H
and
(II) H H
| |
H-C-C=C-C-H
| | | |
H H H H

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