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Amines (A-level only)

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Question 18

Salicylic acid can be prepared from methyl salicylate. Methyl salicylate is first hydrolysed in alkaline conditions as shown:

C6H4(OH)COOCH3+NaOH→C6H4(OH)COONa+CH3OH \text{C}_6\text{H}_4(\text{OH})\text{COOCH}_3 + \text{NaOH} \rightarrow \text{C}_6\text{H}_4(\text{OH})\text{COONa} + \text{CH}_3\text{OH} C6​H4​(OH)COOCH3​+NaOH→C6​H4​(OH)COONa+CH3​OH

A student used the following method:

  1. Add 6.0 cm36.0\text{ cm}^36.0 cm3 of methyl salicylate (density=1.18 g cm−3\text{density} = 1.18\text{ g cm}^{-3}density=1.18 g cm−3, Mr=152.0M_r = 152.0Mr​=152.0) to 40.0 cm340.0\text{ cm}^340.0 cm3 of aqueous 1.5 mol dm−31.5\text{ mol dm}^{-3}1.5 mol dm−3 sodium hydroxide in a round-bottomed flask.
  2. Add a few anti-bumping granules and attach a condenser to the flask. Heat the mixture under reflux for half an hour. Allow the mixture to cool to room temperature.
  3. Pour 50.0 cm350.0\text{ cm}^350.0 cm3 of 1.5 mol dm−31.5\text{ mol dm}^{-3}1.5 mol dm−3 hydrochloric acid into the cooled mixture.
  4. Filter off the precipitate of salicylic acid under reduced pressure.

Questions:

a.

Suggest how the anti-bumping granules prevent bumping during reflux.

[1]
b.

Show, by calculation, that an excess of sodium hydroxide is used in this reaction.

[4]
c.

Suggest why an electric heater is used rather than a Bunsen burner in this hydrolysis.

[1]
d.

Write an equation for the reaction between sodium salicylate and hydrochloric acid.

[1]
e.

In a similar experiment, another student used 0.040 mol0.040\text{ mol}0.040 mol of methyl salicylate and obtained 5.90 g5.90\text{ g}5.90 g of salicylic acid (Mr=138.0M_r = 138.0Mr​=138.0). Calculate the percentage yield of salicylic acid and suggest why the calculated yield is greater than 100%100\%100%.

[3]

Amines (A-level only) Questions

  1. A Level
  2. /Chemistry
  3. /Amines (A-level only)