Question 19M.3.hl.TZ2.b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.hl.TZ2.b |
| Level | hl | 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) is not» [✔]
ALTERNATIVE 2
conductivity [✔]
greater/increased concentration of ions in products [✔]
Note: Do not accept “changes in temperature” or “number of bubbles”.
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+] [✔]
Majority of the candidates stated another property, which could be monitored correctly. The most common error was changes in temperature, which was stated by some candidates.
