Grignard reagents have the general formula $$\(R M g X\)$$, where $$\(R\)$$ is a hydrocarbon group and $$\(X\)$$ is a halogen. The Grignard reagent $$\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{MgBr}\)$$ is used as an intermediate in the reaction between bromobenzene, $$\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Br}\)$$, and ethanal, $$\(\mathrm{CH}_{3} \mathrm{CHO}\)$$, to prepare 1-phenylethanol, $$\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}\)$$. An organic solvent, ethoxyethane, is used. The equations for the three reactions that take place during the preparation are shown. reaction $$\(1 \mathrm{Mg}+\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Br} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{MgBr}\)$$ reaction $$\(2 \quad \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{MgBr}+\mathrm{CH}_{3} \mathrm{CHO} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{OMgBr}\)$$ reaction $$\(3 \quad \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}\left(\mathrm{CH}_{3}\right) \mathrm{OMgBr}+\mathrm{H}^{+} \rightarrow \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}+\mathrm{Mg}^{2+}+\mathrm{Br}^{-}\)$$ The preparation involves the following steps. step1 Set up the apparatus shown in Fig. 1.1 with approximately 1.25 g of Mg powder and $$\(5 \mathrm{~cm}^{3}\)$$ of ethoxyethane in the round-bottomed flask. step 2 Add 0.0500 mol of liquid $$\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Br}\)$$ to the round-bottomed flask dropwise using the tap funnel. Leave until reaction 1 is complete. step 3 Dissolve $$\(3.00 \mathrm{~cm}^{3}\)$$ of $$\(\mathrm{CH}_{3} \mathrm{CHO}\)$$ in $$\(15 \mathrm{~cm}^{3}\)$$ of ethoxyethane and add this solution to the round-bottomed flask using the tap funnel. Leave until reaction 2 is complete. step 4 Remove the condenser, tube $$\(\mathbf{Y}\)$$ and the tap funnel from the round-bottomed flask. step 5 Add $$\(40 \mathrm{~cm}^{3}\)$$ of dilute hydrochloric acid, $$\(\mathrm{HCl}(\mathrm{aq})\)$$, to the round-bottomed flask so that reaction 3 takes place. step 6 Transfer the contents of the round-bottomed flask to a separating funnel. Allow the liquids to settle so that two layers are formed. step 7 Open the tap of the separating funnel and run the lower layer into a beaker labelled $$\(\mathbf{A}\)$$. Run the upper layer into a beaker labelled $$\(\mathbf{B}\)$$. step 8 Allow the ethoxyethane to evaporate from the beaker containing $$\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}\)$$. （i）The overall reaction can be represented as shown in Fig．1．3． （i）At the end of step 8， 2.17 g of 1－phenylethanol is obtained． Determine whether bromobenzene or ethanal is the limiting reagent and hence calculate the percentage yield of 1－phenylethanol． Show your working． ［ $$\(M_{\mathrm{r}}: \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}, 122.0 \mathrm{l}\)$$ percentage yield of $$\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}(\mathrm{OH}) \mathrm{CH}_{3}=\)$$ \％ ［2］ （ii）Suggest why the infrared spectrum of the product detected the presence of a $$\(\mathrm{C}=\mathrm{O}\)$$ peak． . ［1］ ［Total：16］

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