Question 22N.2.SL.TZ0.5
| Date | November 2022 | Marks available | [Maximum mark: 7] | Reference code | 22N.2.SL.TZ0.5 |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Calculate, Discuss, State, Suggest, Write | Question number | 5 | Adapted from | N/A |
Lignite, a type of coal, contains about 0.40 % sulfur by mass.
Calculate the amount, in mol, of sulfur dioxide produced when 500.0 g of lignite undergoes combustion.
S (s) + O2 (g) → SO2 (g)
[2]
«» 2.0 «g» ✔
«» = 0.062 «mol of SO2» ✔
Award [2] for correct final answer.
Accept 0.063 «mol».
A question that discriminated well between high-achieving and low-achieving candidates. The majority of the candidates were able to achieve one mark for determining the number of moles using 500g, while stronger candidates determined 0.40% of 500g to determine the correct number of moles. A number of candidates had a power of ten error in the first step.
Write an equation that shows how sulfur dioxide can produce acid rain.
[1]
SO2 (g) + H2O (l) → H2SO3 (aq)
OR
SO2 (g) + ½O2 (g) → SO3 (g) AND SO3 (g) + H2O (l) → H2SO4 (aq)
OR
SO2 (g) + ½O2 (g) + H2O (l) → H2SO4 (aq) ✔
Accept ionized forms of acids.
This question was poorly answered and only 30% of the candidates wrote a correct equation for the formation of acid rain from SO2. Mistakes included unbalanced equations and hydrogen added as a product.
Sodium thiosulfate reacts with hydrochloric acid as shown:
Na2S2O3 (aq) + 2HCl (aq) → S (s) + SO2 (aq) + 2NaCl (aq) + H2O (l)
The precipitate of sulfur makes the mixture cloudy, so a mark underneath the reaction mixture becomes invisible with time.
Suggest two variables, other than concentration, that should be controlled when comparing relative rates at different temperatures.
[2]
Any two of:
depth/volume «of solution» ✔
colour/darkness/thickness/size/background of mark ✔
intensity of lighting in the lab ✔
Accept same size flask.
Accept position of observation/person observing.
Accept same equipment/apparatus.
Do not accept catalyst/particle size/pressure/time.
Most candidates mentioned "volume" as a variable that should be controlled gaining one of the two marks, while only a small proportion of candidates seemed to understand how the experiment worked and discussed the lighting in the room and the thickness of the mark. The most common incorrect answer was "pressure" which was irrelevant to this experiment.
Discuss two different ways to reduce the environmental impact of energy production from coal.
[2]
Any two of:
remove sulfur from coal ✔
add lime during combustion ✔
not allow sulfur oxides to be released into the environment ✔
reduce proportion/percentage of energy/power produced by «the combustion of» coal ✔
Accept any valid method to wash coal and remove sulfur content for M1.
Accept any valid combustion/post-combustion method to remove sulfur oxides.
Accept any suggestion that would reduce the amount of coal that is burnt or would reduce the damage caused.
Do not accept answers that only reduce production of SO2/CO2 from other fuels.
Accept “improve efficiency of energy production from coal”.
Accept “use coal of lower sulfur content” OR “cleaner coal”.
Some candidates referred to the pre-combustion and post combustion methods of minimizing the release of SO2. Some candidates focused on using cleaner coal, other fuels or renewable energy sources. Some mentioned increasing the efficiency of power stations to reduce the amount of coal burned. Some focused on removing the CO2 released by planting trees. All these options were valid with sufficient detail. But answers that were not relevant to coal, such as fitting catalytic converters on cars, were not accepted. 15% of the candidates did not answer the question, and the average mark was 0.8 out of 2 marks.