Question 1
(a)
(i) State Faraday’s first law of electrolysis.
(ii)Distinguish between a strong electrolyte and a weak electrolyte.
[4 marks]
(b) State one chemical property of ethyne.
[1 mark]
(c)
(i) What is meant by the term unsaturated hydrocarbon?
(ii) Complete the following reaction equation:
CH3COOH + CH3OH
(iii) Name the major product formed in the reaction stated in 1(c)(ii).
[4 marks]
(d)
State one way by which the rate of esterification could be increased.
[1 mark]
(e)
Consider the reaction represented by the following equation:
Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(aq)
If 3.75 g of Zn dust was added to excess H2SO4, calculate the number of molecules of hydrogen gas produced.
[Zn = 65.0; NA = 6.02 x 1023]
[3 marks]
(f) State one effect of global warming.
[1 mark]
(g)
Consider the following reaction equations:
A. Pb(NO3)2 + H2S PbS + 2HNO3;
B. H2 + C2H4 C2H6;
C. Zn(OH)2 + 2OH- [Zn(OH)4}4-
(i) Which of the equations represent(s) redox process?
(ii) State the change in oxidation number of the species that are oxidized or reduced.
[3 marks]
(h)
(i) State two of the main concepts of Bohr’s model of the atom.
(ii) State the limitation of Bohr’s model.
[3 marks]
(i) List three factors that could influence the equilibrium position of a reversible reaction.
[3 marks]
(j)
Calcium trioxocarbonate (IV) powder is added to separate equimolar solutions of hydrochloric acid and ethanoic acid.
State one:
- similarity in the observation in both reaction;
- difference in the observation in both reactions.
[2 marks]
Observation
This question was popular among the candidates and majority of the performed well.
In part (a), majority of the candidates stated the Faraday’s law of electrolysis and distinguished between a strong electrolyte and a weak electrolyte.
In part (b), majority of the candidates were able to sate one chemical property of ethyne.
In part (c), majority of the candidates explained the term unsaturated hydrocarbon and were to complete the reaction equation for the reaction between ethanoic acid and methanol, but could not name the major product formed.
In part (d), majority of the candidates were able to state one way by which the rate of
esterification could be increased.
In part (e), majority of the candidates could not calculate the number of molecules of hydrogen gas produced in the reaction.
In part (f), majority of the candidates stated one effect of global warming.
In part (g), majority of the candidates could not state the change in oxidation number of the species that are oxidized or reduced.
In part (h), candidates could not state the limitation of Bohr’s model.
In part (i), candidates listed three factors that could influence the equilibrium position of a reversible reaction.
In part (j), majority of the candidates did not understand the demand of the question. Instead of stating that a gas was produced, the stated that CO2was produced
The expected answers include:
(a) (i) Faraday’s first law of electrolysis states that the amount of a substance
discharged at / dissolved from an electrode is directly proportional to the
quantity of electricity that passes through the electrolyte.
OR
the mass of an element deposited at the electrode is directly proportional to the quantity of electricity passed.
(ii) Strong electrolytes dissociate / ionize completely in equeous solutions while weak
electrolytes dissociate / ionize only slightly / partially in aqueous solution.
(b) - it burns in air / oxygen
- it undergoes addition reaction
- it undergoes polymerization
- it undergoes substitution / precipitation reaction
(c) (i) hydrocarbon with double / triple bond / multiple bonds between at least a pair
of carbon atoms
(ii) CH3COOH + CH3OH CH3COOCH3 + H2O
(iii) Methylethanoate
(d)
- addition of concentrated H2SO4
- removal of the ester as soon as it forms
- increase the concentration of one of the reactants
(e) 65.0 g of Zn will produce 6.02 x 1023 molecules of H2
OR
65.0 g Zn 1 molecule of H2
3.75g of Zn 3.75 x 6.02 x 1023
65
= 3.47 x 1022molecules
(f)
- sea level rising
- severe climate changes
- depletion of coral reefs
- alters ecosystem balance / setting animals on the move
- severe drought
- flooding of( low-lying areas)
- polar ice melting
(g) (i) equation B / H2 + C2H4 C2H6
(ii) In equation B,
H changes from zero to -1
C changes from +2 to +3
(h) (i)
- an electron in an atom exists / revolves in a circular orbit
- energy of an electron is quantized / has a fixed value
- an electron emits energy in the form of radiation when it moves from a
higher energy state to a lower energy state
(ii) Bohr’s model cannot explain the more complicated spectra lines observed in
spectra other than that of hydrogen
(i)
- Temperature
- Pressure / Volume
- Concentration
(j) (i) Produces a gas / effervescence /bubbles / gas given off
(ii) HCl will produce a more vigorous reaction / CH3COOH will produce a less vigorous reaction