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Aldehydes, ketones, and carboxylic acids are compounds that have a double bond of carbon and oxygen called a carbonyl group. There is an sp2 hybridization of carbon and oxygen in the carbonyl group, and the carbonyl double bond contains one σ-bond and one π-bond. The π electron cloud is found both above and below the plane. The cloud sits between carbonyl carbon and oxygen. The carbonyl group is dipole-shaped because oxygen has a high electronegativity compared to carbon.
- Aldehydes = Carbonyl groups are attached to one hydrogen atom, one alkyl or aryl group, and one carbonyl group in aldehydes.
- Ketones = Ketones are the organic compounds in which the carbonyl group is attached to two alkyl groups or aryl groups or both alkyl and aryl groups.
- Carboxylic Acid = Carboxylic acid is any of a group of organic compounds in which the carbon (C) atom is bonded to the oxygen (O) atom by a double bond and the hydroxyl group (OH) is bonded by a single bond. Carbon atoms are joined by a fourth bond to hydrogen (H) atoms or another type of univalent group. A carboxyl (COOH) group is composed of carbonyl (C=O) and hydroxyl groups.
MCQ on Aldehydes, Ketones and Carboxylic Acids
Ques 1. Ester is formed by a reaction between
- An acid and an alcohol
- An acid and a base
- An alkane and an alcohol
- A ketone and an alcohol
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Ans. (a) An acid and an alcohol
Explanation: Esters are formed when the reaction of an acid and alcohol takes place.
- The reaction is known as the esterification reaction.
- The reaction is
CH3COOH + CH3CH2COOH → CH3COOCH2CH3
- The reaction takes place in the presence of Sulfuric acid (H2SO4).
Ques 2. Vinegar is primarily composed of
- Tartaric acid
- Citric acid
- Acetic acid
- Nitric Acid
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Ans. (c) Acetic acid
Explanation: Vinegar contains acetic acid, also known as ethanol.
- Acetic acid is a colourless liquid with a sour and pungent smell
- In its chemical formula, it has carbon atoms so it is considered to be an organic compound.
Ques 3. Formic acid can reduce
- Tollen's reagent
- Potassium permanganate
- Mercuric chloride
- All of the above
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Ans. (d) All of the above
Explanation: Due to its carboxyl group and aldehyde, formic acid is unique.
- Due to the carbonyl group, this acid reacts with aldehydes in a way that does.
- Aldehydes and acidified KMNO4 are also reduced by this compound.
- In combination with Tollen's reagent, potassium permanganate, and mercuric chloride, formic acid gives a silver mirror.
Ques 4. Soap has a similar cleaning mechanism to:
- Shaping soaps
- Liquid dishwashing detergents
- Toothpaste
- Hair conditioner
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Ans. (b) Liquid dishwashing detergents
Explanation: Soaps are molecules in which two ends have different properties.
- Water interacts with the head, while hydrocarbons interact with the tail.
- Water interacts with the ionic end of soap while oil interacts with the carbon end.
- Consequently, soap molecules are arranged in micelles with one end facing the droplet of oil and the other facing the outside.
- This forms an emulsion in water.
- The soap micelles thus help in pulling out the dirt in water and we can wash our clothes and utensils clean.
Ques 5. What is a characteristic of detergent?
- Hydrophobic
- Hydrophilic
- Both
- None
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Ans. (c) Both
Explanation: Detergents have characteristics similar to that of soap.
- The head of an ant is hydrophilic, since it interacts with water, while the tail is hydrophobic because it interacts with hydrocarbons.
- During soaping, the ionic end interacts with the water, while the carbon ends interact with the oil.
- Soap molecules thus form micelles, structures where the oil droplet is on one end and the outside is on the other.
- Water emulsifies the soap molecules.
- As a result, soap micelles help to remove dirt from water, so that we can wash our clothes and utensils.
Ques 6. An aqueous NaOH solution is added to a mixture of benzaldehyde and formaldehyde to produce
- benzyl alcohol + sodium formate
- sodium benzoate + methanol
- benzyl alcohol + methanol
- sodium benzoate + sodium formate
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Ans. (a) benzyl alcohol + sodium formate
Explanation: When a mixture of formaldehyde and another aldehyde without an α-hydrogen atom is treated with concentrated alkali, it oxidizes formaldehyde to carboxylic acid and reduces another aldehyde to alcohol.
Ques 7. As a result of Wolff-Kishner reduction, the following conversions can be made:
- Benzaldehyde into Benzyl alcohol
- Cyclohexanol into Cyclohexane
- Cyclohexanone into Cyclohexanol
- Benzophenone into Diphenylmethane.
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Ans. (d) Benzophenone into Diphenylmethane
Explanation: Under Wolff Kishner reduction, an aldehyde or ketone is converted into the corresponding alkane.
Ques 8. The formation of cyanohydrin from a ketone is an example of:
- electrophilic addition
- nucleophilic addition
- nucleophilic substitution
- electrophilic substitution
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Ans.(b) nucleophilic addition
Explanation: Since the initial attack is by CN− (nucleophile), it is an example of nucleophilic addition reaction
Ques 9. The process of heating an inorganic compound to produce an organic compound is:
- ammonium cyanate
- soda-lime
- sodamide
- potassium cyanide
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Ans. (a) ammonium cyanate
Explanation: Upon decomposition, ammonium cyanate transforms into an organic compound called urea through the reaction of ammonia and cyanic acid.
Ques 10 Formic acid and acetic acid are distinguished by
- NaHCO3
- FeCl3
- Victor Mayer test
- Tollen's reagent
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Ans. (d) Tollen's reagent
Explanation: Formic acid has an aldehyde group. It reduces Tollen's reagent to a silver mirror-like other aldehydes. Tollen's test is not given by Carboxylic acids.
Ques11. By reacting with Grignard's reagent, other aldehydes than formaldehyde produce additional products that include:
- tertiary alcohols
- secondary alcohols
- primary alcohols
- carboxylic acids
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Ans. (b) secondary alcohols
Explanation: Upon reaction with Grignard's reagent followed by hydrolysis, formaldehyde forms primary alcohol, while all other aldehydes from secondary alcohols.
Ques 12. Which of the following compounds do not react with NaHSO3 ?
- HCHO
- C6H5COCH3
- CH3COCH3
- CH3CHO
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Ans. (b) C6H5COCH3
Explanation: Compared with aliphatic ketones, aromatic ketones are less reactive than aldehydes. The reaction between acetophenone and NaHSO3 is therefore not initiated.
Ques 13. How can Penta-2-one and Pentan-3-one be differentiated?
- Iodoform test
- Benedict’s test
- Fehling’s test
- Aldol condensation test
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Ans. (a) Iodoform test
Explanation: Pentan-2-one is a methyl ketone useful for Iodoform testing.
- Benedict's test will result in both positive results.
- Both tests will be negative for Fehling.
- both can give Aldol.
Ques 14. Toluene is oxidized to benzaldehyde by chromyl chloride is called:
- Etard reaction
- Riemer-Tiemann reaction
- Wurtz reaction
- Cannizzaro’s reaction
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Ans. (a) Etard reaction
Explanation: Oxidation of toluene with chromyl chloride in the Etard reaction gives benzaldehyde. In this reaction, the chromyl chloride first forms a brown complex, which is separated and then decomposed with H2O to give benzaldehyde.
Ques 15. Which compound is obtained when acetaldehydes are treated with a dilute solution of caustic soda?
- Sodium acetate
- Resinous mass
- Aldol
- Ethyl acetate
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Ans. (c) Aldol
Explanation: Aldol is obtained by heating acetaldehyde molecules with dilute NaOH solutions.
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