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Aldehydes, Ketones and Carboxylic Acids — Chemistry STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 ScienceChemistryAldehydes, Ketones and Carboxylic Acids2 Marks
Question
(i) How will you prepare methanol from formaldehyde without using a reducing agent?
(ii) Why is Rochelle salt used in Fehling's solution?
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Answer

By adding concen. NaOH to methanal it will undergoes Cannizzaro reaction and will get two products; one is methanol and another is formic acid salt. In this reaction no external reducing agent is used, methanal itself behave as reducing agent.
$2 HCHO + \underset{\text{conc}}{NaOH} \longrightarrow CH _3 OH + HCOONa$
(ii) In alkaline medium, $Cu ^{2+}$ ions gets precipitated as $Cu ( OH )_2$. Therefore, on adding Rochelle salt, a complex is formed between $Cu ^{2+}$ and tartrate ion (from Rochelle salt) due to which $Cu ^{2+}$ does not remain in the form of ppt. and comes into the solution.

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