2021 NECO Chemistry Answers: 2020 NECO Chemistry Answers Night before Exam

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CHEMISTRY OBJ
1-10: BBDDADEBCA
11-20: BDEABDBCEE
21-30: DEEECCCCEC
31-40: ABDAADCAAB
41-50: EDEDAEADDD
51-60: DBEBABBADA



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(1ai)

(i) graphite
(ii) diamond

(1aii)
(i) animal charcoal
(ii) carbon black

(1aiii)
(i)The property of elements are a periodic function of their atomic number
(ii)Elements are arranged in the periodic table according to the order of increasing in their atomic weight.

(1bi)
Periodicity can be defined as the trend or recurring variation in element properties with increasing atomic number.

(1bii)
using mole = no. of atoms/avogadro's constant
0.5 = No. of atoms/6.023 × 10²³
no. of atoms = 0.5×6.02 × 10²³ = 3.012 × 10²³ atom

(1ci)
Faraday's first law of electrolysis state that the chemical deposition due to the flow of current through an electrolyte is directly proportional to the quantity of electricity (coulombs) passed through it.

(1cii)


2O²^- + 9^e --->2O²
no. of electron = 4
Q=20300C
G.M.V = 22.4dm³.
F = 96500C
Mole = Q/n,f
Mole = 20300/4 × 96500
Mole = 20300/386000
Mole = 0.05mol
Recall; = vol/G.M.V
0.05 = vol/22.4
vol = 0.05 × 22.4
vol = 1.12dm³

(1di)
Using H²SO⁴
H+ SO⁴^-¹
H+ OH^-
A+ Anode
OH ----> OH + e^-
2OH+(aq)+2OH(aq)---->2H²O(s)+O²(aq)



(1dii)
Tabulate
-Electrolyte- (I)teraoxosulphate(iv)acid
(ii)Ester

-non electrolyte-
(iii) phenol

(1ei)
(i) mercury



(1eii)


(i) No. of electron in Y = 16


(ii) No. of mass number = 16 + 18 = 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, <-2P->
↑↓ ↑↓ ↑↑↑

III. Fluorine
1S, 2S, <-2P->
↑↓ ↑↓ ↑↓↑↓↑

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.



2021 NECO Chemistry Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)
=======

(3)

 

(3ai)
Cl2(g) + 2NaOH(aq) + Nacl + H2O(l)
[Cold dilute]

3Cl2(aq) + 6NaOH(aq) + 5Nacl(aq) + 3H2O(l)
[Hot Conc.]

(3aii)
Green to Brown

(3aiii)
DIAGRAM

(3bi)
(i)Hard water tastes better due to dissolved minerals in it
(ii)Hard water helps snails and crabs to make their shells

(3bii)
(i)Exhaust of power plants and vehicles
(ii)Gases from chemical warfare

(3biii)
(i)Starch ---> Iodine
Fats and oil ---> Sudan III

(3ci)
(i)Standard NaOH cannot be accurately prepared because it is deliquescent
(ii)Standard H2SO4 cannot be accurately prepared because it is hydroscopic. Both absorb moisture from the atmosphere.

(3cii)
(i)2,2-dibromo-3,3dimethyl-butane
(ii)2-methyl-Hexane
(iii)Pentan-3-one
(iv)Butan-2-one

(3d)
(i)Boyl’s law states that the volume of a given mass of gas is inversely proportional to its pressure, provided the temperature remains constant.
(ii)V1/T1 = V2/T2 i.e V2 = V1T2/T1
= 400 x (273+150)/(273+30)
Volume at 50°c = 400x323/303 = 426.4cm^3





2021 NECO Chemistry Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)

2021 NECO Chemistry Answers (ESSAY, OBJ, THEORY, PRACTICALS ETC)


(4)

(4ai)
(I) Water is necessary for corrosion to take place whereas burning is different in the presence of water.
(II) Boiling takes place at a specific temperature called boiling point whereas evaporation takes place at all temperatures.

(4bi)
A concentrated solution is one containing large amount of the solute dissolved in water.

(4bii)
(i) The positions of the ions in the electrochemical series.
(ii) The concentration of the ions in the electrolyte.
(iii) The nature of the electrode.

(4ci)
R.M.M = 2[Al] + 3[(S) + 4(O)]
= 2(27) + 3[32 + 4(16)]
= 54 + 3[96]
=342

(4cii)
Aluminium tetraoxosulphate(vi).

(4ciii)
Propane -1,2,3 -triol and salt.

(4di)
(i) Soapless detergents do not form scum with hard water, soaps do.
(ii) Soaps are biodegradable; certain soapless detergents are not and hence cause pollution of water ways.

(4dii)
OH and COOH

(4diii)
v1p1=v2p2 ie v2 = v1p1/p2
= 300×760/800 = 285cm³

(4div)
Change = +13 - 10 = +3

(4dv)
Aluminium ion


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Updated At: April 17th 2021, (06:04:08)

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