Question 19M.3.sl.TZ2.2b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.sl.TZ2.2b |
| Level | sl | Paper | 3 | Time zone | TZ2 |
| Command term | Outline | Question number | b | Adapted from | N/A |
Bromine and methanoic acid react in aqueous solution.
Br2 (aq) + HCOOH (aq) → 2Br− (aq) + 2H+ (aq) + CO2 (g)
The reaction was monitored by measuring the volume of carbon dioxide produced as time progressed.
Outline, with a reason, another property that could be monitored to measure the rate of this reaction.
[2]
ALTERNATIVE 1
colour [✔]
Br2/reactant is coloured «Br– (aq)/product is not» [✔]
Note: Do not accept “changes in temperature” or “number of bubbles”.
ALTERNATIVE 2
conductivity [✔]
greater/increased concentration of ions in products [✔]
ALTERNATIVE 3
mass/pressure [✔]
gas is evolved/produced [✔]
Note: Do not accept “mass of products is less than mass of reactants”.
ALTERNATIVE 4
pH [✔]
methanoic acid is weak AND HBr is strong
OR
increase in [H+] [✔]
The reaction rate was originally monitored by measuring the volume of CO2 produced. Students needed to propose another method for this reaction, with a reason, that could be used to measure the rate. There were several possible correct answers and most students received at least one mark with many receiving both marks. The most common incorrect answer involved changes in temperature.
