Qualitative analysis and organic preparation

Sample questions

Original practice questions written in the style of the exam.

1. Question 14 marks

   A student prepares ethyl ethanoate (boiling temperature $77\,^\circ\text{C}$) by heating ethanol and ethanoic acid with a little concentrated sulfuric acid. The impure distillate contains some ethanoic acid and water.

   Describe how the student should purify the ester.

   Mark scheme

   • Shake the distillate with sodium hydrogencarbonate (or sodium carbonate) solution in a separating funnel to remove acids (1)
   • Release the pressure frequently by opening the tap, as carbon dioxide is produced; run off and discard the aqueous layer (1)
   • Dry the ester by adding anhydrous calcium chloride (or anhydrous sodium sulfate) and filter or decant (1)
   • Redistil and collect the fraction boiling at about $75$–$79\,^\circ\text{C}$ (1)
2. Question 24 marks

   Compound Z has the formula $\text{C}_4\text{H}_8\text{O}$. The results of three tests are shown.

   test	result
   2,4-dinitrophenylhydrazine	orange precipitate
   warm with Fehling's solution	stays blue
   warm with iodine and sodium hydroxide	pale yellow precipitate

   Identify Z, explaining what each test shows.

   Mark scheme