Aldehydes Ketones and Carboxylic Acids Test

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Aldehydes Ketones and Carboxylic Acids Test - 5

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Weekly Quiz Competition

Question 1
1 / -0

The aldehydes and ketones undergo one of the following reactions:

A
nucleophilic addition reactions

B
substitution reaction

C
electrophilic addition reaction

D
None of these

Solution

Aldehydes and Ketones undergoes the characteristic nucleophilic addition reaction. this is because of presence of polar>C=O bond in aldehydes and ketones. due to electronegativity difference between C and O, O bears a small (delta ) negative charge while C bears a small (delta ) positive charge. now because of delta positive charge on C nucleophile can add to >C=O bond giving nucleophilic addition reaction
Question 2
1 / -0

Arrange the following compounds in decreasing order of their acid strength: i) trichloroacetic acid ii) trifluoroacetic acid iii) acetic acid and iv)formic acid

A
trifluoroacetic acid, trichloroacetic acid, formic acid.and acetic acid

B
trifluoroacetic acid, trichloroacetic acid, formic acid and acetic acid

C
trifluoroacetic acid, formic acid acetic acid and Propan – 1 – ol, 4 – methylphenol

D
trichloroacetic acid, trifluoroacetic acid, acetic acid and formic acid.

Solution

Stronger acid always has a stable conjugate base. If RCOOH is acid and its conjugate base is RCOO^-, then the conjugate base of RCOOH will get stabilised when R group contains electron withdrawing group like F (strong -I effect). Stability of the conjugate base will increase the acidity of acid. While if R group is CH₃ which shows electron donation (+I effect), the conjugate base gets destabilised and acidity decreases.
Question 3
1 / -0

CH₃CHO and C₆H₅CH₂CHO can be distinguished chemically by:

A
Tollen's reagent test

B
2,4 DNP test

C
Benedict test

D
Iodoform test

Solution

CH₃CHO will give iodoform test and C₆H₅CH₂CHO will not give iodoform test. Methyl aldehydes or ketones give iodoform test. In carbonyls like RCOR' one of R or R' should be a CH₃ group to give positive iodoform test.

CH₃CHO + NaOI→ CHI₃ + HCOO^-Na⁺

CHI₃ formed is known as iodoform and is yellow precipitate.

C₆H₅CH₂CHO + NaOI → no reaction
Question 4
1 / -0

Which of the following acids does not exhibit optical isomerism?

A
Tartaric acid

B
Lactic acid

C
α – amino acids

D
Maleic acid

Solution

Maleic Acid shows Geometrical Isomerism due restricted bond roation along C=C bond but does not give optical isomerism as it has horizontal plane of symmetry , as C=C bond is planar and thus do not form a non superimposable mirror image and is optically inactive .
Question 5
1 / -0

The compound obtained when acetaldehyde reacts with dilute aqueous sodium hydroxide exhibits:

A
optical isomerism

B
geometrical isomerism

C
neither optical nor geometrical isomerism

D
both optical and geometrical isomerism

Solution

CH₃CHO will react with aq NaOH to give aldol condensation reaction leading to formation of alpha-beta unsaturated aldehyde i.e.CH₃CH=CHCHO

The product which is suitably substituted and has restricted bond rotation along C=C bond and doesn't have any chiral center so it will show only geometrical isomer.
Question 6
1 / -0

Benzaldehyde and acetone can be best distinguished using

A
Tollen's reagent

B
2, 4 – DNP reagent

C
Hydrazine

D
Sodium hydroxide solution

Solution

Tollen's Test is used to distinguish between and aldehyde and ketone. It uses the fact that aldehydes are easily oxidised to their corresponding acids while ketones are not.

Tollen's reagent are aqueous ammonical silver nitrate solution which react with aldehydes as shown.

RCHO + 2Ag⁺ + 2OH^- → RCOO^- + Ag + H₂O.

RCOR + 2Ag⁺ + 2OH → No reaction

If this test is carried in glass tube, the Ag formed forms a mirror on the sides of test tube so the test is also known as silver mirror test.

Aldehydes show tollen’s test while acetone which is a ketone does not give tollen’s test.

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Aldehydes Ketones and Carboxylic Acids Test - 5

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Aldehydes Ketones and Carboxylic Acids Test - 5

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Question 1

nucleophilic addition reactions

substitution reaction

electrophilic addition reaction

None of these

Solution

Question 2

trifluoroacetic acid, trichloroacetic acid, formic acid.and acetic acid

trifluoroacetic acid, trichloroacetic acid, formic acid and acetic acid

trifluoroacetic acid, formic acid acetic acid and Propan – 1 – ol, 4 – methylphenol

trichloroacetic acid, trifluoroacetic acid, acetic acid and formic acid.

Solution

Question 3

Tollen's reagent test

2,4 DNP test

Benedict test

Iodoform test

Solution

Question 4

Tartaric acid

Lactic acid

α – amino acids

Maleic acid

Solution

Question 5

optical isomerism

geometrical isomerism

neither optical nor geometrical isomerism

both optical and geometrical isomerism

Solution

Question 6

Tollen's reagent

2, 4 – DNP reagent

Hydrazine

Sodium hydroxide solution

Solution

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