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

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