jee main chemistry important questions | Aldehydes, Ketones And Carboxylic Acids jee main questions FREE

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Aldehydes give positive Tollen's test.

$RCHO + 2 {[{Ag(NH}_{3})_{2}]}^{+} + 3 {OH}^{-} \to {RCOO}^{-} + 2 Ag + 2 H_{2} O + 4 {NH}_{3}$

So formaldehyde (HCHO) and benzaldehyde ( $C_{6} H_{5} CHO$ ) give silver mirror with ammonical silver nitrate solution.

Formic acid has aldehydic part in it. So it also gives positive Tollen's as well as Fehling's test.

$HCOOH + 2 {[{Ag(NH}_{3})_{2}]}^{+} + 2 {OH}^{-} \to {CO}_{2} + 2 Ag + 2 H_{2} O + 4 {NH}_{3}$

${Co}^{2 +} \overset{H_{2} S gas}{\to} CoS ↓ (Black ppt.)$

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