Waec 2018 Chemistry Obj & Theory Answers – May /June Expo

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Tuesday, 10th April, 2018

Chemistry 2 (Essay) – 2:00 p.m. – 4:00 p.m.

Chemistry 1 (Objective) – 4:00 p.m. – 5:00 p.m.

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_Chemistry Obj_

1-10: ABDCBCABAC

11-20:DACBBACCAA

21-30: CBCDCDAAAB

31-40: AABACBABAA

41-50: DBBDCBCCDB

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1ai)

Fermentation is the process in which a substance breaks down into a simpler substance. Microorganisms like yeast and bacteria usually play a role in thefermentation process, creating beer, wine, bread, kimchi, yogurt and other foods. Fermentation comes from the Latin word fermentare, meaning “to leaven.

(1aii)

Zymase

(1b)

-The strength of an acid

-The PH of the solution

(1c)

Fe+H2SO4->FESO4 + H2

H2SO4=10cm^3

Concentration=1mol/dm^3

Amount=Vol * Concentration

=10/100*1

=0.01mol

1mol=56g

0.01mol=56*0.01

=0.56g

Mass of unreacted=5-0.056

=4.44g

(1di)

Tetraoxosulphate(vi)acid H2SO4(aq)

(1dii)

Cellulose

(1e)

A catalyst increase the rate of chemical reaction by covering the activation of energy of the reaction

(1fi)

CH3COOH +NH3->CH3COONH3+H2(g)

(1fii)

Ethanamide

(1g)

-It is light in weight

-It has resistanc e to rusting

-It has a great tensile strenght

(1h)

-It is used in manufacturing of cosmetics and perfumes

-It is used a s a solvent for cellulose

(1i)

-Heating the solution to its boiling point

-Adding the seed of the salt to precipitate it out

(1j)

-It depletes ozone layer

-It causes earth quake

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(2ai)

Collision theory states that for chemical reaction to occur there must be collision between reactant particles

(2aii)

Increase in temperature can increase the average kinetic energy of the reacting particles thereby increasing the rate of collision of the particles which will eventually result to the formation of the product

(2bi)

DRAW THE GRAPHS

(2bii)

CH3CH2OH +O2->CO2+H2O

or C2H5OH +3O2->2CO2 +3H2O

1 mole of oxygen=22.4dm^3

7.5mole of oxygen= 22.4*7.5=168dm^3

(2ci)

Esterification is the formation of an esther by the reaction between alkanol and an acid

(2cii)

-They are used as solvent for cellulose

-They are used in making perfumes and cosmetics

(2ciii)

CH3COOC2H5(l) + NaOH(aq)<=>CH3COONa(aq)+C2H5OH(aq)

products are: sodium ethanoate and ethanol

(2di)

Galvanized plate

(2dii)

The reason is that tin does not react with atmospheric oxygen while zinc can react with atmospheric oxygen

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(3ai)

H H H H H

| | | | |

H-C-C-C-C-C-C=C-H Heptene

| | | | | |

H H H H H H

(3aii)

The sixth member of Allene C7H14 =

7(molecular mass of carbon) + 14(molecular mass of H)

= 7(12) + 14(1)

= 84 + 14 = 98gmol-¹

(3aiii)

-Cracking is the breaking down of higher molecules into smaller molecules while reforming is the change in the functional group or activity of the compound.

-In cracking more than one product or component is formed. But in reforming one product can still be gotten.

(3bi)

Enthalpy of Neutralization change is the heat change which offers when one mole of H+ from an acid reacts with one mole of OH- from an alkali to form one mole of water.

(3bii)

Weigh about 100cm³ of dil HCL(aq) and that of KOH(aq) of equal volume and put each into a glass calorimeter. The temperature of the two Solutions are taken. The mean volume of the temperature of the acid and base taken. Then quickly transfer the alkali to the acid, turn and take the final temperature of the solution. Record the mass of the mixture. Find the temperature difference.

Total heat covered = mass × specific heat capacity × temperature change.

(3ci)

I - copper

II - silver

(3cii)

Because silver is below copper in the electrochemical series.

(3ciii)

Oxidation - anode

Reduction - Cathode

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(4ai)

DRAW THE DIAGRAM

(4aii)

Na2SO3(aq) +2HCl(aq) ->2NaCl(aq)+H2O(l)+SO2(g)

(4aiii)

Dry the gas evolved by passing it through H2SO4 and collect it by downward delivery

(4aiv)

Because it is denser than air

(4bi)

It states that there is a mixture of gases which do not react chemically together,then the total pressure exerted by the mixture is the sum of the partial pressure of the individual gases that make up the mixture

(4bii)

T1=12C=285K

P1=690mmHg

V1=30cm^3

T2=273K

P2=760mmHg

V2=?

Using general gas law

V1P1/T1=V2P2/T2

V2=V1P1T2/T1P2

=(30*690*273)/(285*760)

V2=26cm^3

(4ci)

Cl2(g)+H20(l)->HCl(aq)+HOcl(aq)

2HOCl(sunlight)->2HCl(aq+O2(g)

(4cii)

Litmus turns red because of the presence of acid HCl

(4di)

Chlorine->Bromine->iodine (increasing boiling point)

(4dii)

Because water has two lone pairs of electrons as compared to ammonia which has one

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(5ai)

-To manufacture ammonia

-Production of fats from vegetable oil

(5aii)

Mg(HCO3)(aq)->MgCO3(g) + H2O(l) + CO2(g)

I-Temporary hardness

II-Waste soap

-Furring kettles

(5bi)

Oxygen is given off which attacks graphite

(5bii)

I-CaO(s) +H2O(l)->Ca(OH)2(aq)

II-Used in treating acid soils

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