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Compound X has molecular formula C₄H₈O - CIE - A-Level Chemistry - Question 37 - 2011 - Paper 1
Question 37
Compound X has molecular formula C₄H₈O. Separate samples of X are tested with three different reagents. Which results could not be obtained? | Tollens' reagent | 2... show full transcript
Worked Solution & Example Answer:Compound X has molecular formula C₄H₈O - CIE - A-Level Chemistry - Question 37 - 2011 - Paper 1
Step 1
Which results could not be obtained?
Answer
To determine which results cannot be obtained, we need to analyze how compound X, with the molecular formula C₄H₈O, will react with the reagents provided.
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Tollens' reagent: This reagent is used to test for aldehydes. The presence of a silver mirror indicates the presence of an aldehyde. Given that compounds with formula C₄H₈O can contain a ketone or an aldehyde, a silver mirror forming result can be obtained. Therefore, a result indicating 'no change' for this reagent cannot be acceptable.
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2,4-dinitrophenylhydrazine reagent: This reagent tests for carbonyl compounds. If a compound reacts, an orange precipitate should form. However, if the compound is an alcohol, we expect no change. Thus, an orange precipitate cannot be expected for a result of 'no change' if X is an alcohol. As for result 2, if there’s no change, it aligns correctly. Hence, a statement claiming that an orange precipitate forms when testing an alcohol is the result that cannot be obtained.
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Warm acidified potassium dichromate(VI) solution: This test is for alcohols, which get oxidized from orange to green. Therefore, a result indicating 'no change' when testing a primary or secondary alcohol is indeed not a valid result, as at least one change is expected.
Combining these observations, we conclude that the results that could not be obtained are those indicating 'no change' for the tests applicable to the respective reagents.