Grignard reagents have the general formula RMgX, where R is a hydrocarbon group and X is a halogen. The Grignard reagent C6H5MgBr is used as an intermediate in the reaction between bromobenzene, C6H5Br, and ethanal, CH3CHO, to prepare 1-phenylethanol, C6H5CH(OH)CH3. An organic solvent, ethoxyethane, is used. The equations for the three reactions that take place during the preparation are shown. reaction 1 Mg + C6H5Br → C6H5MgBr reaction 2 C6H5MgBr + CH3CHO → C6H5CH(CH3)OMgBr reaction 3 C6H5CH(CH3)OMgBr + H⁺ → C6H5CH(OH)CH3 + Mg²⁺ + Br⁻ The preparation involves the following steps. step 1 Set up the apparatus shown in [Figure 1.1] with approximately 1.25g of Mg powder and 5 cm³ of ethoxyethane in the round-bottomed flask. step 2 Add 0.0500 mol of liquid C6H5Br to the round-bottomed flask dropwise using the tap funnel. Leave until reaction 1 is complete. step 3 Dissolve 3.00 cm³ of CH3CHO in 15cm³ 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 Y and the tap funnel from the round-bottomed flask. step 5 Add 40 cm³ of dilute hydrochloric acid, HCl(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 A. Run the upper layer into a beaker labelled B. step 8 Allow the ethoxyethane to evaporate from the beaker containing C6H5CH(OH)CH3. Some relevant data are shown in Table 1.1. Table 1.1 substance density /gcm⁻³ boiling point /°C hazard bromobenzene 1.50 156 flammable, toxic, skin irritant distilled water 1.00 100 non-hazardous ethoxyethane 0.714 35 flammable, toxic ethanal 0.788 21 flammable, eye and respiratory irritant 1-phenylethanol 1.01 204 flammable, toxic, eye irritant

1. (a)Use the information in Table 1.1 to suggest why the following safety precautions are used. • wearing chemically resistant gloves • using a fume hood[2]
2. (b)(i)Suggest how the glassware shown in [Figure 1.1] should be dried before use in step 1.[1]
3. (b)(ii)The ethoxyethane contains a small amount of water. Suggest how the water can be removed from the ethoxyethane before use in steps 1 and 3.[1]
4. (c)(i)Draw a labelled arrow on [Figure 1.1] to show where the water enters the condenser.[1]
5. (c)(ii)Suggest why solid Z is used.[1]
6. (c)(iii)Give one reason why the apparatus does not have a bung at the end of tube Y.[1]
7. (d)In step 1, approximately 1.25g of Mg powder is needed. Outline how the student should accurately weigh by difference using a weighing boat so that the exact mass of Mg transferred into the flask is known. Include a results table, with appropriate headings, ready for the student to fill in.[2]
8. (e)Use the information in Table 1.1 to determine the volume, in cm³, of bromobenzene used in step 2. [Mᵣ: C₆H₅Br, 156.9] volume of C₆H₅Br = ...................................... cm³[1]
9. (f)The bromobenzene is added dropwise in step 2. Suggest one reason why the bromobenzene is not added all at once.[1]
10. (g)Suggest why a measuring cylinder is a suitable piece of apparatus to measure 40cm³ of hydrochloric acid in step 5.[1]
11. (h)The separating funnel used in steps 6 and 7 is shown in [Figure 1.2]. The final product, 1-phenylethanol, is in the ethoxyethane layer. State whether beaker A or beaker B contains the layer with 1-phenylethanol after step 7. Explain your answer using the information given in Table 1.1. beaker ..................................................... explanation ............................................................................................................................................................................................................................................[1]
12. (i)(i)At the end of step 8, 2.17g 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. [Mᵣ: C₆H₅CH(OH)CH₃, 122.0] percentage yield of C₆H₅CH(OH)CH₃ = ...................................... %[2]
13. (i)(ii)Suggest why the infrared spectrum of the product detected the presence of a C=O peak.[1]

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