Question 20N.3.sl.TZ0.2b
| Date | November 2020 | Marks available | [Maximum mark: 2] | Reference code | 20N.3.sl.TZ0.2b |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Explain | Question number | b | Adapted from | N/A |
An investigation was carried out to determine the effect of chain length of the alcohol on the equilibrium constant, , for the reversible reaction:
The reactants, products and the catalyst form a homogeneous mixture.
Fixed volumes of each alcohol, the ethanoic acid and the sulfuric acid catalyst were placed in sealed conical flasks.
At equilibrium, the flasks were placed in an ice bath, and samples of each flask titrated with to determine the ethanoic acid concentration present in the equilibrium mixture.
The following processed results were obtained.
© International Baccalaureate Organization 2020
The ice bath is used at equilibrium to slow down the forward and reverse reactions. Explain why adding a large amount of water to the reaction mixture would also slow down both reactions.
[2]
dilution/lower concentrations ✔
less frequent collisions «per unit volume» ✔
Accept “lowers concentration of acid catalyst” for M1. M2 must refer to increase in activation energy or different pathway.
Do not accept responses referring to equilibrium.
A significant number of students scored at least one mark, usually the first and many both. Weaker students lost the second mark by referring to less collisions instead of less frequent collision or other words to this effect. Very few students referred to more diluted catalyst and of those even less were able to provide an adequate explanation in terms of the increased Ea. Many students tried to answer this question in terms of equilibrium instead of kinetics. There were also several responses that replied as if the dilution would only occur for part of the reaction or individual reactants instead of the entire solution.
