Formalin is a water-based saturated solution of formaldehyde gas. The aqueous solution of formaldehyde 40 % is known as formalin. It is used as an industrial disinfectant and also used for preserving biological specimens.

Write short notes on the stephen reaction.

Alkyl nitriles undergo reduction with the help of tin (II) chloride and hydrochloric acid and form an intermediate imine salt which undergoes hydrolysis with water, giving the final result as aldehydes. R − CN + 2 [ H ] → SnCl 2 / dil . HCl R − CH = NHHCl → H 2 O R − CHO + NH 4 Cl

Explain the following reaction: Cannizzaro reaction

Cannizzaro's reaction: The self oxidation-reduction (disproportionation) reaction of aldehydes which do not have α -hydrogen atom, on treatment with concentrated alkali is known as the Cannizzaro's reaction. In this reaction, two molecules of aldehydes participate where one is reduced to alcohol and the other is oxidised to carboxylic acid. For example, when methanal is treated with concentrated potassium hydroxide, methanol and potassium methanoate are produced. 2 HCHO → Con . KOH CH 3 OH + HCOOK

E M B I B E

Chemistry Standard 12>Chapter 12 - Aldehydes, Ketones and Carboxylic Acids>Exercises>Q 2

MEDIUM

12th Maharashtra Board

IMPORTANT

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Name the product obtained by the oxidation of $1, 2, 3, 4 -$ tetrahydronaphthalene with acidified potassium permanganate.

Important Questions on Aldehydes, Ketones and Carboxylic Acids

EASY

12th Maharashtra Board

IMPORTANT

Chemistry Standard 12>Chapter 12 - Aldehydes, Ketones and Carboxylic Acids>Exercises>Q 2

What is formalin?

EASY

12th Maharashtra Board

IMPORTANT

Chemistry Standard 12>Chapter 12 - Aldehydes, Ketones and Carboxylic Acids>Exercises>Q 2

Arrange the following compounds in the increasing order of their boiling points: Formaldehyde, ethane and methyl alcohol.

MEDIUM

12th Maharashtra Board

IMPORTANT

Chemistry Standard 12>Chapter 12 - Aldehydes, Ketones and Carboxylic Acids>Exercises>Q 2

Acetic acid is prepared from methyl magnesium bromide and dry ice in presence of dry ether. Name the compound which serves not only reagent but also as cooling agent in the reaction.

HARD

12th Maharashtra Board

IMPORTANT

Chemistry Standard 12>Chapter 12 - Aldehydes, Ketones and Carboxylic Acids>Exercises>Q 3

Observe the following equation of the reaction of Tollens’ reagent with an aldehyde. How do we know that a redox reaction has taken place. Explain.

$R - CHO + 2 Ag {({NH}_{3})}_{2}^{+} + {OH}^{-} \overset{∆}{\to} R - COO^{-} + 2 Ag ↓ + 4 {NH}_{3} + 2 H_{2} O$