Question 1
- (a) (i) Define the term electrolysis.
(ii) state one Factor that influences the preferential discharge of ions during electrolysis. [3 marks]
(b) Define rate of chemical reaction. [2 marks]
(c) State why iodide ions are stronger reducing agents than chloride ions. [2 marks]
(d) (i) Write an equation for the reaction of chloride with hot concentrated NaOH.
(ii) State what type of reaction occurs in 1d(i). [3 marks]
(e) An alkanoic acid has a molar mass of 74 gmol-1.
(i) Draw its structural formula.
(ii) Write the IUPAC name.
(H=1.0, C=12.0, O=16.0) [5 marks]
(f) (i) Why is water described as a universal solvent?
(ii) What would be observed when acidified solution of KMnO4 reacts with SO2?
(g) (i) Complete the following reaction equations:
CH3COOH + NaOH
(ii) name the major product formed in the reaction in 1 (g)(i).
(iii) name the type of reaction that occurred in 1(g)(i). [3 marks]
(h) If a piece of copper metal was placed in separate solutions of silver trioxonitrate (V) and zinc trioxonitrate (V).
(i) State which of the solutions would undergo a reaction;
(ii) what type of reaction takes place in the copper metal? [2 marks]
(i) Explain briefly why nitrogen has a higher 1st ionization energy than oxygen.
[2 marks]
(j) Name the following compound:
| CH3CHCH2CH3
| CH2
CH3 [1 mark]
Observation
Majority of the candidates responded to this question and their performance was average.
In part (a), defined the term electrolysis and stated one factor that influences the preferential discharge of ions during electrolysis.
In part (b), majority of the candidates defined rate of chemical reaction correctly.
In part (c), majority of the candidates could not state why iodide ions are stronger reducing agents than chloride ions.
In part (d), majority of the candidates could not write an equation for the reaction of chlorine with hot concentrated NaOH..
In part (e), majority of the candidates could not draw the structure of the alkanoic acid from the given molar mass.
In part (f), majority of the candidates were able to give the reason why water is described as a universal solvent.
In par (g), majority of the candidates could not balance the reaction equation.
In part (h), majority of the candidates could not state which of the solutions would undergo a reaction.
In part (i), majority of the candidates could not explain briefly why nitrogen has a higher 1st ionization energy than oxygen.
In part (j), only few candidates could name the organic compound.
The expected answers include:
(a) (i) It is the decomposition of an electrolyte / solution of compound / molten
Compound by passing electric current through it.
(ii)
- position of ion in the electrochemical series
- concentration of ions / electrolyte
- nature of electrodes
(b) Rate of a chemical reaction is the change in concentration / amount of a reactant or a product per unit time.
(c) The outer electrons in the iodide ion are further from the nucleus / more shielded so the iodide ion loses electrons more easily (than the chloride ion)
(d) (i) 3Cl + 6NaOH → 5NaCl + NaClO3 + 3H2O
(ii) Disproportionation / Redox reaction
(e) (i) CnH2n+1COOH
12n + 2n + 1 + 12 + 32 + 1 = 74
14n + 46 = 74
14n = 74 – 46
14n = 28
n = 2
H H O
| | //
H – C – C – C \
| | O – H
H H
All bonds and atoms must be shown
(ii) - Propanoic acid
(f) (i) Because it dissolves most substances
(ii) The (deep) purple colour of the solution is discharged / it turns colourless / it is decolourised
(g) (i) CH3COOH + NaOH → CH3COONa + H2O
(ii) Sodium ethanoate
(iii) Neutralization
(h) (i) Silver trioxonitrate (V) solution / AgNO3(aq) / AgNO3 solution
(ii) Oxidation
(i) Outermost electrons in oxygen are paired in orbital / outer electrons in nitrogen are
Unpaired hence repulsion between paired electrons makes it easier to remove outermost electron of oxygen
(j) 3 – methylpentane