A student wants to investigate the rate of the hydrolysis of methyl methanoate, HCOOCH3. HCOOCH3 + H2O ⇌ HCOOH + CH3OH The reaction is catalysed by dilute hydrochloric acid, HCl(aq). The amount of methanoic acid, HCOOH, produced as the reaction progresses can be monitored by titration with aqueous sodium hydroxide, NaOH(aq), of known concentration using thymolphthalein as the indicator. To determine this, the volume of NaOH(aq) needed to neutralise the H+(aq) from the catalyst needs to be found beforehand. The student uses the following procedure. step 1 Add approximately 150 cm³ of iced water to a 250 cm³ conical flask, A. step 2 Add 200 cm³ of 0.250 moldm-3 HCl(aq) to a 500 cm³ conical flask, B. Conical flask B is the flask in which the reaction takes place. step 3 Transfer 2.00cm³ of 0.250moldm¯³ HCl(aq) from conical flask B to conical flask A. Carry out a single titration of the contents of conical flask A with NaOH(aq) of known concentration. step 4 Add 10.0cm³ of methyl methanoate to conical flask B, swirl the reaction mixture and immediately start a stopwatch. step 5 After 1 minute transfer 2.00cm³ of the reaction mixture from conical flask B into conical flask A. Carry out a further single titration of the contents of conical flask A against NaOH(aq). Do not empty the contents of conical flask A between titrations. step 6 After 10 minutes transfer 2.00 cm³ of the reaction mixture from conical flask B into conical flask A. Titrate the contents of conical flask A against NaOH(aq). step 7 Repeat step 6 at intervals of 10 minutes for 1 hour.

1. (a)State which step is used to determine the concentration of H+(aq) ions from the catalyst in the mixture.[1]
2. (b)The iced water in conical flask A is used to significantly reduce the rate of reaction. Suggest two reasons why the rate of reaction is significantly reduced when the reaction mixture is transferred to conical flask A. reason 1 reason 2[2]
3. (c)(i)Complete Table 2.1.[2]
4. (c)(ii)Identify the independent variable.[1]
5. (c)(iii)Identify one variable that needs to be controlled, apart from concentrations and volumes of solutions.[1]
6. (c)(iv)Reading 2 should have been taken at 10 minutes and not at 13 minutes. State whether this result should have been included or not. Explain your answer.[1]
7. (c)(v)Plot a graph on the grid in Fig. 2.1 to show the relationship between (V∞ – Vt) and time. Use a cross (x) to plot each data point. Draw a line of best fit.[2]
8. (c)(vi)Reading 5 was not taken. Use the graph to predict the total volume of NaOH(aq) needed to neutralise the total amount of H+(aq) at 40 minutes. volume of NaOH(aq) =[1]
9. (c)(vii)It is not possible to repeat the experiment. State whether the data from the experiment is reliable. Justify your answer.[1]

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