2nd PUC Chemistry Question Bank Chapter 12 Aldehydes, Ketones and Carboxylic Acids

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Karnataka 2nd PUC Chemistry Question Bank Chapter 12 Aldehydes, Ketones and Carboxylic Acids

Question 1.
Mention the hybridised state of carbonyl carbon.
Answer:
sp² hybridised.

Question 2.
Give the IUPAC name of CH₃CHO.
Answer:
Ethanal.

Question 3.
Give the IUPAC name of CH₂ = CH – CHO
Answer:
Prop-2-enal.

Question 4.
Write the IUPAC name of CH₃COCH₂CH₂CH₃.
Answer:
Pentan-2-one.

Question 5.
Explain Rosenmund reduction of benzoyl chloride.
Answer:
When benzoyl chloride (acid chloride) is hydrogenated with catalyst, palladium on barium sulphate, benzaldehyde is obtained.

Question 6.

Name the reaction.
Answer:
Rosenmund reduction.

Question 7.
How would you prepare acetaldehyde from acetyl chloride?
Name the reaction.
Answer:
When acetyl chloride undergoes hydrogenation using palladium on barium sulphate catalyst acetaldehyde is obtained. The reaction is called Rosenmund reduction reaction.

Question 8.
Explain Etards reaction.
Answer:
When toluene is oxidised by chromylchloride benzaldehyde is obtained.

Question 9.
Which oxidising agent is used in Etard reaction?
Answer:
Chromyl Chloride (CrO₂Cl₂).

Question 10.

Write the name of the above reaction.
Answer:
Etard’s reaction.

Question 11.
How benzene is converted into benzaldehyde by Gattermann-Koch reaction?
Answer:
When benzene is treated with carbon monoxide and hydrogen chloride in presence of anhydrous aluminium chloride benzaldehyde is obtained.

Question 12.
Complete the reaction

Answer:

Question 13.
How ketone is obtained from Friedel craft’s acylation reaction?
Answer:
When benzene is treated with acid chloride in presence of anhydrous aluminium chloride ketone is obtained.

Question 14.

Write the structure of X in the above reaction.
Answer:

Question 15.
Write the organic compound formed in the following reaction.

Answer:

Question 16.
Explain the mechanism of addition of HCN to a carbonyl group in presence of a base.
Answer:
Aldehydes and ketones react with hydrogen cyanide in presence of base to yield cyanohydrins.

Question 17.
Explain the addition of ammonia and its derivatives with aldehydes and ketones.
Answer:
Nucleophiles such as ammonia and its derivatives H₂N-Z add to carbonyl group of aldehydes and ketones in presence of acid to form intermediate which

Question 18.
What happens when the carhonyl compounds are treated with hydrazine? Write the reaction.
Answer:
Carbonyl compounds react with hydrazine to form hydrazones.

Question 19.
Complete the reaction

Answer:

Question 20.
Write the organic compound formed in the following reaction.

Answer:

Question 21.
How does propanone (CH₃COCH₃) reacts with hydrazine? Give equation,
Answer:
Propanone undergoes nucleophilic addition reaction with hydrazine forming addition product hydrazone.

Question 22.
Most of ketones does not give addition compound with sodium bisulphite. Give reason.
Answer:
Due to steric. hindrence.

Question 23.
Give reason: Acetophenone does not react with saturated sodium bisulphite solution.
Answer:
Due to steric hindrence.

Question 24.
Aldehydes are generally more reactive than ketones towards nucleophilic addition reactions. Give two reasons.
Answer:
(a) No steric hindrence for the attack of nucleophile on carbonyl carbon.
(b) Carbonyl carbon of aldehydes is more electrophilic than the carbonyl carbon of ketones.

Question 25.
Name the reagent used in the conversion of ketone to hydrocarbon. Name the reaction.
Answer:
Zinc-Amalgam and Cone, hydrochloric acid. The name of the reaction is Clemmensen reduction.

Question 26.
Complete and name the following reactions.

Answer:
(a)

(b) Clemmensen reduction.

Question 27.
Explain Wolff-Kishner reduction.
Answer:
Aldehydes and ketones can be reduced to hydrocarbons by the action of hydrazine and the intermediate is heated with KOH in ethylene glycol solvent.

Question 28.
What are P and Q?

Answer:

Question 29.
What is Tollen’s reagent? How it reacts with aldehydes?
Answer:
Tollen’s reagent is an ammonical solution of silver nitrate. On warming an aldehyde with freshly prepared Tollen’s reagent a bright silver mirror is produced due to the formation of silver metal.
RCHO + 2[Ag(NH₃)₂]⁺ + 3OH^– → RCOO^– + 2Ag + 2H₂O + 4NH₃

Question 30.
What is Fehlings solution? How it reacts with aldehydes?
Answer:
Fehlings solution is a alkaline solution of copper sulphate solution containing sodium potassium tartarate. On heating an aldehyde with Fehlings solution a reddish brown precipitate is obtained. Fehlings solution oxidises aldehyde to carboxylate anion.
R-CHO + 2Cu²⁺ + 5OH^– → RCOO^– + Cu₂O + 3H₂O

Question 31.
Explain haloform reaction.
Answer:
Aldehydes and ketones having atleast one methyl group linked to the carbonyl carbon atom are oxidised by sodium hypohalite to the sodium salt of corresponding carboxylic acid. Methyl group is converted into haloform. This reaction is called haloform reaction.
Example:

Question 32.
Explain iodoform reaction.
Answer:
When aldehydes and ketones having at least one methyl group linked to the carbonyl atom undergoes iodoform reaction when it is warmed with iodine and sodium hydroxide solution.

Question 33.
Give the IUPAC name of X.

Answer:
Triiodomethane.

Question 34.
Give reason: ∝-hydrogen atoms of aldehydes and ketones are acidic.
Answer:
The acidity of ∝-hydrogens is due to the strong electron withdrawing effect of the carbonyl group and the resonance stabilisation of the conjugate base.

Question 35.
Explain aldol codensation with an example.
Answer:
Aldehydes and ketones having atlleast one ∝-hydrogen undergo a reaction in the presence of dilute alkali as catalyst to form p-hydroxy aldehydes (aldol) or p-hydroxy ketones (ketol). The aldol and ketol, on heating readily lose water to give, ∝, β-unsaturated carbonyl compounds. This reaction is called aldol condensation.

Question 36.
What is the action of dil. NaOH on ethanal (acetaldehyde)? Name the reaction.
Answer:
Aldehydes and ketones having atleast one ∝-hydrogen undergo a reaction in the presence of dilute alkali as catalyst to form p-hydroxy aldehydes (aldol) or p-hydroxy ketones (ketol). The aldol and ketol, on heating readily lose water to give, ∝, β-unsaturated carbonyl compounds. This reaction is called aldol condensation.

Question 37.
Write the name of the reaction.

Answer:
Aldol condensation (ketol).

Question 38.
What is cross aldol condensation. Give an example.
Answer:
When aldol conservation is carried out between two different aldehydes or ketones it is called crossed aldol condensation.
Example:

Question 39.
How does benzaldehyde reacts with acetophenone in presence of dilute alkali.
Answer:
Benzaldehyde undergoes crossed aldol condensation with acetophenone in presence of alkali forming benzalacetophenone.

Question 40.
Ethanal (CH₃CHO) undergoes aldol condensation reaction. Give reason.
Answer:
Ethanal contain ∝-hydrogens.

Question 41.
Explain Cannizzaro reaction with an example.
Answer:
Aldehydes which do not have an ∝-hydrogen atom, undergo self-oxidation and reduction reaction on heating with cone, alkali.

In this reaction one molecule of the aldehyde is reduced to alcohol while another is oxidised to carboxylic acid salt.

Question 42.
Identify A and B in the following reaction.

Answer:

Question 43.
Acetaldehyde does not undergo Cannizzaro reaction. Why?
Answer:
Because acetaldehyde has ∝-hydrogens.

Question 44.
Formaldehyde undergoes Cannizzaro’s reaction. Give reason.
Answer:
It does not contain ∝-hydrogen atom.

Question 45.
Give two uses of formaldehyde.
Answer:
(a) 40% aqueous solution of formaldehyde called formalin used to preserve biological specimens.
(b) Formaldehyde is used to prepare bakelite (phenol-formaldehyde resin).

Question 46.
How are carboxylic acids prepared from Grignard reagents?
Answer:
Grignard reagents react with solid carbon dioxide (dry ice) to form salts of carboxylic acids, which on acidification gives carboxylic acid.

Question 47.
What are Y and Z in the following reactions.

Answer:
Y → solid CO₂ (dry ice), Z → R – COOH

Question 48.
Complete the following reaction.

Answer:
R-COOH
Carboxylic acid.

Question 49.
Complete the following reaction?

Answer:

Question 50.
How are carboxylic acids prepared from nitriles?
Answer:
Nitriles are hydrolysed to carboxylic acids in the presence of H⁺ or OH^– as catalyst at hot condition.

Question 51.
“Carboxylic acids are more acidic than phenols”. Give reason.
Answer:
The conjugate base of carboxylic acid is carboxylate ion. The conjugate base of phenol is phenoxide ion. Resonance stabilisation is more in carboxylate ion than phenoxide ion. Hence carboxylic acids are more acidic than phenols.

Question 52.
Explain the effect of electron withdrawing groups [EWG] on the acidity of carboxylic acids. Give examples. [3M]
Answer:
Electron withdrawing groups [EWG] increases the acidity of carboxylic acids by stabilising the carboxylate ion (conjugate base) through delocalisation of the negative charge by inductive and /or resonance effect.
Examples:
(a) Chloroacetic acid is more acidic than acetic acid due to the presence of EWG of Cl.
ClCH₂COOH > CH₃COOH

(b) Benzoic acid is more acidic than acetic acid due to the presence of EWG of Phenyl group.
C₆H₅COOH > CH₂COOH

Question 53.
What is the effect of electron withdrawing group on the acidity of carboxylic acid?
Answer:
Increases.

Question 54.
Explain the effect of electron donating group (EDG) on the acidity of carboxylic acids. Give example.
Answer:
Electron donating groups (EDG) decreases the acidity of carboxylic acids by destabilising carboxylate ion (conjugate base).
Acetic acid is less acidic than formic acid.

Question 55.
Among formic acid and acetic acid, which is more acidic? Give reason.
Answer:
Formic acid is more acidic, because stability of acetate ion is less due to the + 1 effect of methyl group.

Question 56.
How PCl₃ PCl₅ and SOCl₂ reacts with carboxylic acids?
Answer:

Question 57.
Write the chemical equation to convert ethanoic acid to ethanoic anhydride.
Answer:

Question 58.
Write the equation for
(i) The reaction between carboxylic acids and PCl₅.
(ii) The reaction between formaldehyde and Cone. KOR.
(iii) The formation of oxime from carbonyl compound.
Answer:
(i) R – COOH + PCl₅ → R-COCl + POCl₃ + HCl
(ii) 2HCHO + KOH → CH₃OH + HCOOK

Question 59.
A carboxylic acid is heated with alcohol in presence of Conc. H₂SO₄.
Name the reaction. Give its general equation.
Answer:
Esterification reaction
R-COOH + R¹-OH → R-COOR¹ + H₂O

Question 60.
Complete the equation.

Answer:

Question 61.
How carboxylic acids react with ammonia?
Answer:
Carboxylic acids react with ammonia to give ammonium salt which gives amides on further heating.

Question 62.
How do you convert benzoic acid to benzamide? Write the equation.
Answer:
Benzoic acid reacts with ammonia to give ammonium benzoato, which on heating gives benzamide.

Question 63.
What is the major product of the following reaction.

Answer:

Question 64.
Explain decarboxylation reaction with an example.
Answer:
Carboxylic acids lose CO₂ to form hydrocarbons when their sodium salts are heated with soda lime.

Question 65.
What is soda lime?
Answer:
Soda lime is a mixture of NaOH and CaO in 3:1 ratio. It is called decarboxylation reagent.

Question 66.
Explain HVZ reaction with example.
Answer:
Carboxylic acids having an °c-hydrogen are halogenated at the -position on treatment with chlorine or bromine in presence of red phosphorus to give ∝-halo-carboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction.

Question 67.
Complete the equation.

Answer:

Question 68.
Complete the reaction.

Answer:
CH₄ + Na₂CO₃