2018 WAEC GCE CHEMISTRY THEORY AND OBJECTIVE ANSWERS – JANUARY/FEBRUARY EXPO​

CHEMISTRY OBJ

VERIFIED CHEMISTRY OBJ:

1-10: ACCDDAADAA

11-20: DCDABBDCAA

21-30: CBCBCCCADB

31-40: CCBDCCBACD

41-50: CBDA.C….SOLVE REST OBJ BY URSEF

CHEMISTRY THEORY

(1a) 

A compound is the chemical combination of two or more elements.

(1b)

-Presence of large molecule.

-Presence of heat.

-Presence of catalyst..

(1c)

-Nickel, Manganese.

-Platinum, Zinc OR Iron

(1di)

Zn(s) + 2AgNO3—>Zn(NO3)2 + 2Ag(s)

(1dii)

I. Ag is reduced

II. Zn is oxidized

(1e)

16

O – 90% abundance

8

16

O – 10% abundance

8

= The relative atomic mass Ar = (16×90/100) + (18×10/100)

= 1440/100 + 180/100 = 1440+180/100

= 1620/100 = 16.20

(1f)

The ores of iron are:

-Hematitie(Fe2O3)

-Magnetide(Fe3O4) 

(1gi)

Biotechnology is the optimism exploitation of biological processes for industrial and other purposes. It is the branch of science that exploits  microorganisms fot the production of antibiotics, hormones, etc.

(1gii)

Antibiotics

(1h)  An element is a substance which can not be further divided by an ordinary chemical reaction.

(1i)

– fossil fuel for burning

– Biomass burning

– wetlands

(1j)

It is because the dipole induced dipole bonds are stronger in iodine than in bromine and than in chlorine ie there are more electrons in iodine than in bromine and that in chlorine

++++++++++++++++++++++++++

(2a)

It means that the standard electrode potential difference set-up between Zinc and one-molar solution of its ion at 298K

(2b) 

(i) Zn²(Aq) + / Zn(s) —- cathode

Cu/ Cu²+(aq) ——- anode

(ii) Zn²+(aq)/Zn(s)  // Cu  / Cu²+

(iii)

At the cathode —- reduction

At the anode —– Oxidation.

(iv) EΦ   =   EΦ   –  E

= 0.34-(-0.76)

= 0.34+0.76

=  +1.10V

(2ci)

– Chemical and allied products industries

– sunshine oil and chemical industries

– Eleme petrochemical industries

(2cii) source of raw materials

Nearness to market

Source of amenities

2ciii) 

-Pollution of air (surrounding)

-Land excavation and improper with disposal

(2di)

Ag2O(s) +H2O2= 2Ag(s)+ O2(g)+H2O(l)

(2dii)

H2O2 + Cl2 => 2HCl(g) + 2H2)(l)

(2e)

-It is an inert  gas

-It is slightly denser than air

-It is slightly soluble in water

++++++++++++++++++++++++++

(3a)

From the passage of steam through a mass of hot coke at

a very high temperature (about 1000 oC).

The water gas is mixed with more steam and passed over iron

(III) oxide (as catalyst) at 450 o C. More hydrogen is produced

and carbon(II) oxide gets oxidized to carbondioxide. ie The carbondioxide is removed by dissolving the above products in water under 30 atm pressure – CO2 dissolves.

The gas is then passed through copper(I) methanoate in

ammonia solution under pressure to absorb any trace of carbon(II) oxide which might be present as impurity if not

removed – the hydrogen produced is pure.

(3aii)

C (s) + H 2 O(g) → CO (g) + H 2(g)

(3aiii)

(i)  By the action of a dilute strong acid on metals, such as zinc:

(ii) By reaction amphoteric metals with a strong base, such as sodium hydroxide:

(iii) By electrolysis of water:

(3b)

(i) Decrease in temperature shifts reaction towards product side.

(ii) Increase in pressure shifts reaction towards reactant  side.

(iii) Increase in concentration of CO will increase the yield of the product.

(3ci)

Condensation polymerisation is a process whereby many

small monomer molecules join together to form one large polymer, with water, or some other small molecule formed at the same time.

(3cii)

(i) polyamides

(ii) polyacetals

(3ciii)

CH3−COO−CH2−CH3,

(3di)

Allotropy is the existence of a chemical element in two or more forms, which may differ in the arrangement of

atoms in crystalline solids or in the occurrence of molecules that contain different numbers of atoms.

(3dii)

-diamond,

-graphite

(3diii)

-Diamond is used for cutting hard substance.

-Graphite is used  to make brake linings, lubricants, and molds in foundries

(3e)

TABLULATE:

(i)

Nitrogen (I) Oide:

-No rection with nitrogen(II)oxide

Oxygen:

-Forms reddish brown fumes with nitrogen(II)oxide

(ii)

Nitrogen (I) Oide:

-Sweet smell

Oxygen:

-Odourless