CAP1 (y13)

Question 1

Methanol can be manufactured in a reversible reaction as shown by the equation. CO(g) + 2H2(g) ⇌ CH3OH(g)
(a) State and explain the effect of using a catalyst on the yield of methanol in this equilibrium

Answer 1

no effect (on yield)
CE = 0 if yield changes
2.increases rate / speed of both / forward and reverse reactions equally / by the same amount

(

Question 2

Give an expression for the equilibrium constant (Kc) for this reaction.

CO(g) + 2H2(g) ⇌ CH3OH(g)

Answer 2

Must be square brackets products on top / reactants on bottom

Question 3

(c) A mixture of carbon monoxide and hydrogen was allowed to reach equilibrium in a container of volume 250 cm3 at temperature T.
At equilibrium, the mixture contained 0.340 mol of carbon monoxide, 0.190 mol of hydrogen and 0.0610 mol of methanol.
Calculate the value of the equilibrium constant (Kc) for this reaction at temperature T.
CO(g) + 2H2(g) ⇌ CH3OH(g)

Answer 3

0.311

Question 4

This question is about Group 7 chemistry.
(a) Give an equation for the reaction of solid sodium bromide with concentrated sulfuric acid to form bromine.
State one observation made during this reaction.

Answer 4

2H2SO4 + 2NaBr → Na2SO4 + SO2 + Br2 + 2H2O
allow ionic and equation forming NaHSO4
3H2SO4 + 2NaBr → 2NaHSO4 + SO2 + Br2 + 2H2O
2H+ +2Br- +H2SO4 →SO2 +Br2 +2H2O
not equation from HBr unless formation of HBr shown in separate equation
M2 orange/brown fumes/solution
not liquid / yellow solid / bad eggs smell / white ppt
ignore choking gas/fumes / steamy/white fumes

Question 5

solution that is thought to contain chloride ions and iodide ions is tested.
1. Dilute nitric acid is added to the solution.
2. Aqueous silver nitrate is added to the solution.
3. A pale yellow precipitate forms.
4. Excess dilute aqueous ammonia is added to the mixture.
5. Some of the precipitate dissolves and a darker yellow precipitate remains.
Give a reason for the use of each reagent.
Explain the observations. (5)
Give ionic equations for any reactions.

Answer 5

HNO3 removes (hydroxide/carbonate) ions that may give other ppts with AgNO3
AgNO3 produces ppts with chloride/iodide/halide
not chlorine/iodine/halogen Ag+(aq) + Cl−(aq) → AgCl(s) OR
Ag+(aq) + I−(aq) → AgI(s)
allow Ag+(aq) + X−(aq) → AgX(s)
state symbols not required but not if wrong
NH3 dissolves AgCl (leaving yellow AgI)
allow chloride/iodide salt/ppt AgCl(s) + 2NH3(aq) → [Ag(NH3)2 ]2+ + Cl−(aq)

Question 6

Benzene reacts with ethanoyl chloride in a substitution reaction to form C6H5COCH3. This reaction is catalysed by aluminium chloride.
(a) Write equations to show the role of aluminium chloride as a catalyst in this reaction.
Name the product, C6H5COCH3.

Answer 6

CH3COCl + AlCl3 CH3CO+ + AlCl4–

AlCl4– + H+ AlCl3 + Hl

Phenylethanone

Question 7

When methylbenzene reacts with ethanoyl chloride and aluminium chloride, a similar substitution reaction occurs but the reaction is faster than the reaction of benzene.
Suggest why the reaction of methylbenzene is faster.

Answer 7

c) M1 about electrons
methyl group has (positive) inductive effect OR increases electron density on benzene ring OR pushes electrons OR is electron releasing

Ignore reference to delocalisation
M2 about attraction

electrophile attracted more
or benzene ring better nucleophile
Allow intermediate ion stabilised
M2 only awarded after correct or close M1