Most Repeated MDCAT Chemistry: Aldehydes and Ketones MCQs

Explanation

Ketones are prepared by the oxidation of secondary alcohols. When a secondary alcohol is oxidized, it loses hydrogen atoms and forms a ketone. Primary alcohols, on the other hand, are oxidized to form aldehydes, while tertiary alcohols cannot be oxidized to form ketones or aldehydes. So, it's the secondary alcohols that are used to prepare ketones.

Explanation

Tollens' reagent is a chemical reagent used to determine the presence of an aldehyde, aromatic aldehyde and alpha-hydroxy ketone functional groups. The reagent consists of a solution of silver nitrate and ammonia.

Explanation

Cannizzaro's reaction is not given by aldehydes and ketones that have alpha hydrogen (hydrogen next to carbonyl carbon). In formaldehyde, there are no α Hydrogen so it will undergo this reaction. Acetaldehyde has 3 α Hydrogens next to C=O group so it cannot undergo this reaction. In trimethyl acetaldehyde, 3 CH3​ groups are attached to α Carbon and no α Hydrogen so it will undergo this reaction. In benzaldehyde, there is benzyl group on α carbon so it does not have α Hydrogen and it will undergo this reaction.

Explanation

Aldehydes and ketones have a carbonyl group (C=O) as a functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon (RCOR’). The simplest ketone is acetone, which has two methyl groups attached to the carbonyl carbon (CH3COCH3). An aldehyde is similar to a ketone, except that instead of two side groups connected to the carbonyl carbon, they have at least one hydrogen (RCOH or R-CHO). The simplest aldehyde is formaldehyde (HCOH), as it has two hydrogens connected to the carbonyl group. All other aldehydes have one hydrogen bonded to the carbonyl group, like the simple molecule acetaldehyde, which has one hydrogen and one methyl group (HCOCH3).

Explanation

Aldehydes on oxidation give carboxylic acids. As methanoic acid is carboxylic acid, so, option B is correct.

Explanation

Acetone is prepared by dry distillation of calcium acetate.Hence, option A is correct.

Explanation

Ketones on oxidation give carboxylic acids with 1 carbon atom less than ketone. Since acetone contains 3 carbon atoms, it will form a carboxylic acid with 2 carbon atoms which is ethanoic acid or acetic acid.Hence, option B is correct.

Explanation

When toluene is subjected to oxidation, only the methyl group undergoes oxidation while the benzene ring remains intact. The methyl group on oxidation given carboxyl group.So, the product will be benzoic acid.Hence, option D is correct.

Explanation

Beneze is oxidized in presence of vanadium peroxide (V2O5) producing maleic anhydride.STB Pg- 157Hence, option D is correct.

Explanation

Fehling's solution is used to test for the presence of reducing sugars and aldehydes. Ketones do not typically react with Fehling's solution because they lack the necessary functional group (an aldehyde) to reduce the copper(II) ion in the solution to copper(I) oxide. This is why ketones do not show a positive test with Fehling's solution.Conclusion: The correct answer is Fehling's Solution, which ketones do not react with, while the other options represent reactions that ketones typically undergo.

Explanation

Formaldehyde (HCHO) is the most reactive towards nucleophilic addition among the given options. This is because formaldehyde is the simplest aldehyde with a hydrogen atom attached to the carbonyl carbon. The presence of a highly reactive hydrogen atom makes formaldehyde more susceptible to nucleophilic attack compared to other aldehydes. Therefore, option a is correct.

Explanation

The correct answer is Alcohol. During catalytic reduction, hydrogen is added to the carbonyl group of aldehydes and ketones, converting them into alcohols. Specifically, aldehydes yield primary alcohols, while ketones yield secondary alcohols. The other options are incorrect because: Carboxylic acids are produced from the oxidation of alcohols, not their reduction; Alkanes do not form from the reduction of carbonyl compounds; and Aldehydes are the reactants in this reduction process, not the products.