2018 Waec Gce Chemistry Obj And Theory Questions And Answers Now Available Here

Waec Gce Chemistry Portal
CHEMISTRY OBJ:
1-10: CCDBACBABA
11-20: BDDDCDBAAA
21-30: CAADCCCAAB
31-40: CBBCABCDBC
41-50: BACCAABACC

(1a)
Gas > liquid > Solid

(1aii)
Solid > liquid > gas

(1bi)
PH>7

(1bii)
PH>7

(1ci)
(I) Magnesium from 0 to +2
(II) Hydrogen changes from 1 to 0

(1cii)
I —> Magnesium is oxidized
II —> Hyfrogen is reduced

(1ciii)
HCL

(1di)
(i) Boiling occurs throughout the entire volume while evaporation occurs at the surface
(ii)It involves the formation of bubbles while evaporation does not form bubbles

(1dii)
It decreases the boiling point as the boiling point of water is proportional to the magnitude of atmosphere pressure.

(1e)
It dictates the rate of reaction and also optimize the amount of product formed.

(1f)
C3H7CooH —> Butanoic acid
(CH3)3COH —> Butan-1-ol

(1g)
Functional groups are responsible for their different chemical behavior or properties so that organic compounds with smaller functional group would behave similarly.

(1h)
Solids in liquid:
(i) It depends on the nature of temperature changes or exothermic or endothermic as affect by the temperature of the liquid.
(ii) The surface area of solid is lesser, they dissolves less as compound to gases in the same volume.
(iii) Pressure does not affect the solubility of the solids

Gas in liquid:
(i) It depends on the average kinetic energy as affect by temperature of the liquid.
(ii) The surface area of gases are higher so they dissolve more in a given volume of water.
(iii) The solubility of gases is a direct consequences of pressure changes due to the partial pressure of the gas molecules.

(1i)
3F2 + 3H2O -> 6HF + O3

(1j)
Basicity of an acid is the number of replaceable hydrogen ions in the acid.

2ai)
carbon – 0.48/12 , 0.04/0.04 , 1
hydrogen – 0.08/1 , 0.08/0.04 , 2
chlorine – 1.42/35.5 0.04/0.04 , 1
Therefore CH2CL
The electrical formular = CH2CL
2aii)
The molar mass of the compound is 99
Hence (CH2CL)n = 99
(12 + 2C1) + 35.5)n = 99
12 + 2 + 35.5
(495)n = 99
Therefore n = 2
Hence the molar formula = (CH2CL)2
C2H4CL2

(2b)
(i) It is soluble in water and in other Polar solvents.
(ii) NaCl(s) when dissolves in water ionizes to form Na+ and Cl-
(iii) The aqueous solution of NaCl(s) can be used as an electrolyte.

(2c)
2H2 + O2 -> 2H2O
E0 = 285.5kgmol^-1

(i)
Draw the diagram

(ii)
Ea1 – activation kinetic energy for uncatalyzed reaction.
Ea2 – activation energy for catalyzed reaction.

(2di)
Ethene – from liquefied petroleum Gas. (L.P.A)

(2dii)
Cracking

(2diii)
(i) Ethene
(ii) Ehloroethene

(2div)
Ethene is obtained either by the cracking of heavy hydrocarbons to get other higher products including ethene or as a component of LPA or by the action of dehydration of ethanol. While Chloroethene is produced by the addition reaction of ethene.

(3ai)
When potassium chloride dissolves in water, the bond in the solid particle breaks thereby increasing the kinetic energy of the particle to move. Particles in solid state have restricted or static movement unlike those in the form of ions or gases.

(3aii)
It is endothermic because it involves bond breaking and heat is absorbed in the process.

(3bi)
An underground iron pipe is less likely to erode if it is bonded at intervals with magnesium rod because the magnesium is more electro positive thereby absorbing the water or little oxynegn it is exposed to. In addition, corrosion is influenced by the presence of oxygen and water, therefore underground iron pipe will be exposed to little oxygen and water.

(3bii)
(i) First, conversion of Iron II to Iron III
Fe²+(aq) + e- —>Fe³+(aq)

(ii) Exposure to oxygen and water vapour.
4Fe(s) + 3O2(g) + xH2O(l) –> 2Fe2O3 xH2O
Iron rod Iron rust

(3biii)
The iron in water will be oxidized since there is dissolved oxygen and atmospheric oxygen & a brown deposit of Iron occurred.

(3ci)
A spontaneous reaction is a reaction that can exist freely on its own without any external factor. A reaction is said to be spontaneous if ΔG, is the Gribb’s free energy is negative. ΔG = -ve
An example is rusting of Iron.

(3cii)
(i) When Gribb’s free energy is negative.
(ii) When Entropy ie Δs must be positive as the total entropy must increase.

(3Ciii)
This is because sodium is more electropositive than calcium. Also the heat evolved in the reaction with sodium is far greater than the heat of solution released with calcium and water at the same temperature.

(3civ)
2Na(s) + 2H2O(l) —> 2NaOH(aq) + H2(g)
Ca(s) + 2H2O(l) —> Ca(OH)2 + H2(g)

(3d)
Mass of lead (ii) trioxocarbonate iv
PbCO3
= 207 + 12 + 3(16)
207 + 12 + 48 = 267g
1mole of PbCO3 contain 1 mole of Pb
267g of PbCO3 = 207g of Pb
Xg of PbCO3 = 35.0g of P
X = 267×35/207 = 45.1g
=45.1g of PbCO3

(3e)
(i) Covalent bond
(ii) Ionic bond

(5ai)
(i)Carbon (II) oxide
(ii) Carbon (iv) oxide

(5aii)
It is because there is increasing surface area of the broken coal than in the lumps of coal

(5aiii)
CH4

(5aiv)
Coke

(5bi)
SO2

(5bii)
MnO2

(5biii)
Sodium oxide

(5biv)
Aluminium oxide

(5bv)
NO2 gas

(5ci)
Cl2+FeCl—–>FeCl3

(5cii)
Redox reaction

(5ciii)
Iron(ii) ion is oxidized to iron(iii) ion
ie Fe2+ –> Fe3+

(5di)
A = Delivery tube
B = Calcium oxide

(5dii)
Ca(OH)2+2NH4Cl –> CaCl2+2NH4.H2O

(5diii)
Ammonia gas

(5div)
The gas is less dense than air

(5dv)
(I) B is used to drive the gas
(II) Upward delivery

(5e)
Petrol