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Which compound reacts with 2,4-dinitrophenylhydrazine reagent but does not react with Tollens' reagent? A CH₃COCO₂H B CH₃CH(OH)CHO C CH₃COCHO D CH₃CH(OH)CH₃ - CIE - A-Level Chemistry - Question 23 - 2018 - Paper 1
Question 23
Which compound reacts with 2,4-dinitrophenylhydrazine reagent but does not react with Tollens' reagent? A CH₃COCO₂H B CH₃CH(OH)CHO C CH₃COCHO D CH₃CH(OH)CH₃
Worked Solution & Example Answer:Which compound reacts with 2,4-dinitrophenylhydrazine reagent but does not react with Tollens' reagent? A CH₃COCO₂H B CH₃CH(OH)CHO C CH₃COCHO D CH₃CH(OH)CH₃ - CIE - A-Level Chemistry - Question 23 - 2018 - Paper 1
Step 1
Identify the Reagent Properties
Answer
2,4-dinitrophenylhydrazine (DNPH) is used to identify carbonyl compounds, specifically aldehydes and ketones. It forms a yellow or orange precipitate when it reacts with these compounds. Tollens' reagent, on the other hand, specifically identifies aldehydes through oxidation, while ketones typically do not react.
Step 2
Evaluate Each Compound
Answer
A. CH₃COCO₂H: This is a ketone which would react with DNPH.
B. CH₃CH(OH)CHO: This is an aldehyde and would react with both DNPH and Tollens' reagent.
C. CH₃COCHO: This is also an aldehyde and will react with both reagents.
D. CH₃CH(OH)CH₃: This is a secondary alcohol that will not react with Tollens' reagent but can give a positive test with DNPH.
Step 3