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You are provided with samples of each of the four compounds - AQA - A-Level Chemistry - Question 7 - 2017 - Paper 2
Question 7
You are provided with samples of each of the four compounds. K L M N Describe how you could distinguish between all four compounds using the minimum number of t... show full transcript
Worked Solution & Example Answer:You are provided with samples of each of the four compounds - AQA - A-Level Chemistry - Question 7 - 2017 - Paper 2
Step 1
Test 1: NaOH and Mg Indicator
Answer
Add sodium hydroxide (NaOH) to each sample followed by a magnesium indicator.
- Observation:
- For compound K (carboxylic acid), a color change will occur indicating the presence of the -COOH group.
- Compounds L and M will not exhibit any color change since they do not contain the -COOH group in their structure.
- Compound N will also show no reaction.
Step 2
Test 2: Bromine Water
Answer
Add bromine water to samples L, M, and N.
- Observation:
- Compound L does not react, remaining brown, indicating a saturated carbon chain.
- Compound M will decolorize the bromine water due to the presence of a double bond (alkene), indicating unsaturation.
- Compound N will show no reaction.
Step 3
Test 3: Fehling's Solution or Tollens' Reagent
Answer
Add Fehling's solution or Tollens' reagent to sample N.
- Observation:
- Compound N, being an aldehyde, will reduce the reagent, resulting in a color change (brick-red precipitate with Fehling's solution or a silver mirror with Tollens').
- Compounds K, L, and M do not show a positive result for this test.