WAEC GCE Jan/Feb 2019 Chemistry & Essay Expo Answer

(1a)

Helium’ ^4 He has a stable electron configuration compound Be because it has a complete filled valance electron.

(1bi)

– After forming an ionic bond.

1H becomes H^+ : it will have zero electron 

– After forming an ionic bond.

3Li^+ becomes 3Li^+ : it will have two electrons 

(1bii) 

– 1H^+ had one electron while neutral. On forming an ionic bond, it loses one electron 

– 3Li^+ had 3 electrons while neutral. On forming an ionic bond, it loses one electron 

(1ci)

Raw materials should be easily and cheaply obtainable 

(1cii)

Means of transport

(1d)

(i)low evolution of heat

(ii)low energy waste

(1e)

No of moles of chlorine reacting = 21.3/71= 0.3moles

From the equation, ratio at temperature to chlorine is 1:8

No of moles of temperature = 0.3/8 = 0.0375

Using the no. of moles = mass/molar mass 

Mass of turpentine = 0.0375 x 136 = 5.1g

(1f)

Cr@cking means breaking down or decomposition of compound by the action of the heat alone

(1g)

(i)stability

(ii)size of atomic ratio 

(1h)

Carbohydrates are naturally occurring organic compound containing hydrogen and oxygen with the hydrogen and oxygen present in the ratio of 2:1

(1i)

(i)A simple sugar is crystalline, starch is not

(ii)A simple sugar is soluble in water , starch is not 

(1j)

(i)H2CO2/ H2CO3—–>2H^+CO3^2-

(ii)CH2COOH/CH2COOH—–>CH2COO^1

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(2ai)

(i)dilute acids and metal (soluble salt)

(ii)Alkali and acid (soluble salt)

(iii)double decomposition 

(2aii)

(i)dilute acids and metal (soluble salt):

Zn(s) + 2HCl(aq)———>ZnCl(aq) + H2(aq)

(ii)Alkali and acid (soluble salt): NaOH(aq)+HNO3(aq)—–>NaNO3(aq)+H2O(s)

(iii)double decomposition:AgNO3(aq)+NaCl(aq)——>AgCl(s)+NaNO3(aq)

(2aiii)

(i)used in manufacturing of glass

(ii)used to standardized acid in the laboratory

(2b)

The impure copper is made the anode in an electrolytic cell containing pure copper and cathodes and copper (II) tetra oxo-sulphate VI solutions as the electrolyte 

At cathode

4OH^(aq)—->2H2O(s) + (aq) + 4e

At anode 

Cu(s)—–>Cu^2+(aq)+2e

(2c)

for sodium chloride = 39.0-36.6/39.0*100%

=2.7/39*100%

=0.0692*100%

=6.92%

for siliver nitrate = 952-297/952*100%

=655/952*100%

=68.8%

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(3a)

(i)all elements are made up of small indivisible particles called atoms

(ii)atoms can nither be create nor destoryed

(iii)when atoms combine with other atoms they do so in simple ratios

(3aii)

law of multiple proportion state when two or more elements/compounds have multiple ways of combining into different compounds.

(3bi)

-margarine

-soap

-candles

3bii) CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH + 2H2(g) ———> CH3(CH2)6COOH

CH3(CH2)14COOC2H5 + NAOH——-> CH3(CH2)14COONa + C2H5OH

(4ai)

Hardness of water is a situation whereby water does not lather well with soap which is causes by dissolution of some salts like CaSO4 and MgSO4 in the water. 

(4aiii) 

(i) It causes furging of kettles and boilers. 

(ii) It causes waste of soap and water. 

(4bi) Ammonia NH3, OxygenO2

(4bii) Ammonia is poured over heated platinum rhodium catalyst at 700°c to produce NO and steam which then in the presence of excess air gives NO2. It is then sprayed with hot water to form HNO3

(4biii) S + HNO3 —> H2SO4(aq) + H2O(l) + 6NO2(aq)

Aluminum does not react with conc. HNO3 due to the formation of protective coating of oxide on the metal. 

(4c) 

Al2O3 Aluminium oxide.

5ii

???? Carbon dioxide is colorless

.???? At low concentrations the gas is odorless;

5eii

???? Carbon dioxide is an acidic oxide and reacts with water to give carbonic acid. 

???? Carbon dioxide reacts with alkalis to give carbonates and bicarbonates.
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