Question 3
- Consider the following reaction equation:
(i) What type of reaction is represented by the equation?
(ii) Write the molecular formula of X.
(iii) Draw the structure of two isomers of X.
(iv) Name the isomers drawn in 3 (a) (iii).
(v) Write a balanced equation for the reaction between X and hydrogen. [ 8 marks ] - Describe one test for fats. [ 3 marks ]
- Sulphur (IV) oxide is converted to tetraoxosulphate (VI) according to the following equation:
If 1.5 moles of oxygen reacts with sulphur (IV) oxide, calculate the mass of tetraoxosulphate (VI) acid produced. [H = 1.0; O = 16.0; S = 32.0] [ 4 marks ] - Consider the following neutralization reactions:
(i) Arrange the enthalpy changes for the reactions in order of increasing magnitude.
(ii) Explain briefly your order in 3(d)(i). [ 7 marks ] - Consider the following substances.
Cu(s), BeCl2(s), NaH(s), HF(l) and CCL4(l).
State the substance(s) which:
(i) can conduct electricity;
(ii) is / are soluble in water.
Observation
This question was not compulsory. The response of candidates to the question was fair.
In part (a), majority of the candidates could not identify the reaction represented by the equation as catalytic cracking, because they could not could not differentiate between thermal cracking and catalytic cracking.
In part (b), majority of the candidates could not describe one test for fats. However, those that described it used white paper test.
In part (c), majority of the candidates could not calculate the mass of H2SO4 produced if 1.5 moles of O2 react with sulphur (IV) oxide.
In part (d), majority of the candidates could not arrange the enthalpy changes of the given reactions in order of increasing magnitude, because they could not relate enthalpy changes to the strength of acids and bases.
In part (e), majority of the candidates did not know that ionic compounds in the solid state do not conduct electricity. Furthermore, they did not know that compound CCl4(l) has covalent bond, and will not be soluble in water.
The expected answers include:
- (i) Catalytic cracking Do not accept cracking
(ii) C4 H8
(iii)
(iv) A - But-1-ene
B - But-2-ene
C - 2-methylpropene
(Name must correspond with structure to score)
(v) C4 H8 + H2 → C4H10 -
Place a small amount of the substance on a (filter) paper and rub / warm / melt. The formation of a translucent spot on the filter paper shows the presence of fats.
OR
Treat fat with sudan III reagent / Add sudan III to fat . A red colour is observed -
(ii) Neutralization involves the combination of H+ and OH- ions to give a specific amount of energy .
The greater the ionization the greater the energy given off
∆H2 involves a weak acid and a weak base / weak electrolyte.
∆H1 involves a strong base and a weak acid
∆H3 involves a strong acid and a strong base- (i) Cu(s)
(ii) NaH(s), BeCl2 (s), HF(l)