18/11/2020
A. 2020 NECO CHEMISTRY (OBJECTIVES) ANSWERS:
1-10: BBDDADEBCA
11-20: BDEABDBCEE
21-30: DEEECCCCEC
31-40: ABDAADCAAB
41-50: EDEDAEADDD
51-60: DBEBABBADA
B. 2020 NECO CHEMISTRY (ESSAY) ANSWERS:
(1a)
(i)Diamond
(ii)Graphite
(1aii)
(i)Coal
(ii)Coke
(1aiii)
(i)Elements with similar properties recur at regular intervals or periods
(ii)The properties of the elements are a periodic function of their atomic numbers
(1b)
(i)Periodicity is the variation of the properties of elements in a regular pattern both down the groups and across the periods.
(ii)1 mole contains 6.023 x 10^23 atoms
0.5 moles of oxygen contains 0.5 x 6.023 x 10^23 atoms
= 3.0115 x 10^23 atoms
(1ci)
Faraday’s first law of electrolysis states that the mass(m) of an element discharged during electrolysis is directly proportional to the quantity of electricity(Q) passing through it.
(1cii)
No. of moles, N = Q/Fe = 20300/96500x4 = 20300/386000 = 0.05259
volume of oxygen librated at s.t.p = 0.05259 x 22.4
=0.1178dm^3
(1di)
Cathodic half cell reaction: 4H+(aq) + 4^e- ---> 2H2(g)
Anodic half cell reaction: 4OH-(aq) ---> 2H2O(i) + O2(q) + 4^e-
(1dii)
Tetraoxosulphate(iv)acid ---> Electrolyte
Ester ---> Non-electrolyte
Phenol ---> Non-electrolyte
(1ei)
Mercury
(1eii)
(i)Number of electrons = 16
(ii)M-16 = 18 (no. of neutrons)
M=18+16 = 34
Mass number = 34
(iii)Sulphur
(2ai)
The basicity of an acid is the number of replaceable hydrogen ions N+ in one molecule of the acid.
(2aii)
(i) H3p04 ---> basicity = 3
(ii) HC00H ---> basicity = 1
(iii) H2S04 ---> basicity = 2
(2bi)
-Temperature of the reacting system
-Pressure of the reacting system
-Concentration of the reacting system
(2bii)
-Nature of reactants
-Concentration/Pressure of reactants
-Surface area of reactants
(2ci)
In a tabular form
Under S/N
I, II
Under Indicator:
Methyl orange, Phenolphthalein
Under colouric acid:
Pink, Colourless
Under colour of endpoint:
Orange, colourless
Under colour in base:
Yellow, pink
Under suitable for:
Strong acid and weak base,
Weak acid and strong base
(2cii)
I. Nitrogen
1S, 2S,
↑↓ ↑↓ ↑↑↑
III. Fluorine
1S, 2S,
↑↓ ↑↓ ↑↓↑↓↑
II. Aluminium
1S, 2S, 2P, 3S, 3P
↑↓ ↑↓ ↑↓↑↓↑↓ ↑↓ ↑
(2di)
(i) Heat is evolved liberating hydrogen gas
(ii) Decolourization of purple KMn04 with deposit of sulphur
(iii) Black residue of carbon due to dehydration
(2dii)
(i) Glucose is used as an immediate source of energy for sick people and sportsmen
(ii) It is used in the manufacture of sweets.
(3ai)
Cl2(g) + 2N
