Q: The percentage of formaldehyde in formalin is:

$ 40 \% $. Formalin is the common laboratory solution of formaldehyde, and its standard concentration is about 37–40%. Therefore, the correct option is 40%.

Question 1

An aldehyde on oxidation gives

Accepted Answer

an acid. Aldehydes oxidize easily because they have a hydrogen attached to the carbonyl carbon. Oxidation converts the aldehyde group into a carboxylic acid group.

Question 2

The percentage of formaldehyde in formalin is:

Accepted Answer

$ 40 \% $. Formalin is the common laboratory solution of formaldehyde, and its standard concentration is about 37–40%. Therefore, the correct option is 40%.

Question 3

The addition compound obtained by treating propanone with hydrogen cyanide is:

Accepted Answer

propene cyanohydrin. Propanone reacts with HCN to form its cyanohydrin, where CN and OH add to the former carbonyl carbon. Since the starting ketone has three carbons, the product is propene cyanohydrin in the given options.

Question 4

Carboxylic acids dissolve in NaHCO3 and evolve CO2 gas but phenols do not.

Accepted Answer

Carboxylic acids dissolve in NaHCO3 and evolve CO2 gas but phenols do not.. Carboxylic acids react with NaHCO3 to form a salt, water, and CO2 gas due to their stronger acidity compared to phenols, which do not react with NaHCO3.

Question 5

Which of the following compounds undergoes oxidation to give acetic acid?

Accepted Answer

CH3—CH=CH—CH3. CH3—CH=CH—CH3 (option A) undergoes oxidation to give acetic acid because the double bond allows for cleavage and oxidation to form carboxylic acids. The other compounds lack the necessary functional group or structure for this reaction.

Question 6

The relative reactivities of acyl compounds towards nucleophilic substitution are in the order of:

Accepted Answer

(a) Acyl chloride > Acid anhydride > Ester > Amide. The reactivity of acyl compounds towards nucleophilic substitution depends on the leaving group ability and the electrophilicity of the carbonyl carbon. Acyl chlorides are the most reactive due to the excellent leaving ability of Cl⁻, followed by acid anhydrides, esters, and amides (which have poor leaving groups).

Question 7

Aldehydes are more reactive than ketones due to +I effect of CH3 group. There are two CH3 groups in acetone which reduces +ve charge density on carbon atom of carbonyl group. More hindered carbonyl group too becomes less reactive. So, in the given case CH3CHO is the right choice.

Accepted Answer

CH3CHO > CH3COCH3. Aldehydes are more reactive than ketones because ketones have two alkyl groups that exhibit +I effect, reducing the electrophilicity of the carbonyl carbon. Additionally, steric hindrance in ketones further decreases their reactivity. Thus, CH3CHO is more reactive than CH3COCH3.

Question 8

Among the given compounds, the most susceptible to nucleophilic attack at the carbonyl group is:

Accepted Answer

(d) CH₃COCl. Acyl chlorides (CH₃COCl) are the most reactive towards nucleophilic attack due to the strong electron-withdrawing effect of the chlorine atom, which increases the electrophilicity of the carbonyl carbon.

Question 9

Which one of the following orders of acid strength is correct?

Accepted Answer

RCOOH > HOH > ROH > HC ≡ CH. Carboxylic acids (RCOOH) are the strongest acids among the given options due to resonance stabilization of their conjugate base. Water (HOH) is more acidic than alcohols (ROH) because alcohols have an electron-donating alkyl group that reduces acidity. Alkynes (HC≡CH) are the least acidic due to the lack of resonance stabilization in their conjugate base.

Question 10

In the following reaction: HC≡CH (H2SO4, Hg2+) → 'P'. Product 'P' will not give

Accepted Answer

Tollen’s reagent test. The reaction converts HC≡CH into acetaldehyde (CH3CHO). Acetaldehyde gives a positive iodoform test, Brady's reagent test, and Victor Meyer test but does not give a positive Tollen's reagent test as it is not an aromatic aldehyde.

Question 11

Compound A, C8H10O, is found to react with NaOI (produced by reacting Y with NaOH) and yields a yellow precipitate with characteristic smell. A and Y are respectively

Accepted Answer

CH–CH3 and I2. Compound A (C8H10O) reacts with NaOI to form a yellow precipitate of iodoform, indicating the presence of a methyl ketone group. Y is I2, which reacts with NaOH to produce NaOI. Thus, A is CH3–CO–CH3 (acetophenone) and Y is I2.

Question 12

Reaction by which Benzaldehyde cannot be prepared:

Accepted Answer

CO (d). The question seems incomplete or unclear, but based on typical benzaldehyde preparation methods, the reaction involving CO (d) might not align with standard methods like Gattermann-Koch or Rosenmund reduction.

Question 13

Consider the following reaction:

COCl
H2
Pd-BaSO4 → 'A'

The product 'A' is:

Accepted Answer

C6H5CHO. The reaction described is the Rosenmund reduction, where an acid chloride (COCl) is reduced to an aldehyde (C6H5CHO) using hydrogen gas in the presence of Pd-BaSO4 as a catalyst.

Question 14

Ketones

R—C—R1, where R = R1 = alkyl groups
||
O

can be obtained in one step by

Accepted Answer

hydrolysis of esters. Ketones can be obtained in one step by the hydrolysis of esters, as the ester bond breaks to form a ketone and an alcohol.

Question 15

The catalyst used in Rosenmund's reduction is:

Accepted Answer

Pd/BaSO4. Rosenmund's reduction involves the reduction of acid chlorides to aldehydes using hydrogen gas in the presence of palladium (Pd) supported on barium sulfate (BaSO4) as a catalyst.

Question 16

Pinacolone is

Accepted Answer

3, 3-Dimethyl-2-butanone. Pinacolone is the common name for 3,3-dimethyl-2-butanone, a ketone derived from the rearrangement of pinacol (a diol).

Question 17

Which of the following reactions will not result in the formation of carbon-carbon bonds?

Accepted Answer

Cannizzaro reaction. The Cannizzaro reaction involves the disproportionation of aldehydes without alpha-hydrogens into alcohols and carboxylic acids, and does not form carbon-carbon bonds. The other reactions involve carbon-carbon bond formation.

Question 18

Reaction between benzaldehyde and acetophenone in presence of dilute NaOH is known as

Accepted Answer

Cross Aldol condensation. The reaction between benzaldehyde (an aldehyde without an alpha-hydrogen) and acetophenone (a ketone with an alpha-hydrogen) in the presence of dilute NaOH is a cross aldol condensation, as it involves two different carbonyl compounds.

Question 19

Of the following, which is the product formed when cyclohexanone undergoes aldol condensation followed by heating?

Accepted Answer

Structure (b). Cyclohexanone undergoes aldol condensation to form a β-hydroxyketone intermediate, which upon heating undergoes dehydration to yield an α,β-unsaturated ketone. This matches structure (b).

Question 20

The product formed by the reaction of an aldehyde with a primary amine is:

Accepted Answer

Schiff base. When an aldehyde reacts with a primary amine, it forms an imine, commonly referred to as a Schiff base, through a condensation reaction.

NEET Chemistry: Aldehydes, Ketones and Carboxylic Acids questions with solutions

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