Q: What is the IUPAC name of acetaldehyde?

The IUPAC name of acetaldehyde is ethanal — derived from the two-carbon chain eth- and the aldehyde suffix -al. Acetaldehyde is the retained common name; ethanal is the preferred systematic name (CAS 75-07-0).

Q: What is the molecular formula of acetaldehyde?

The acetaldehyde molecular formula is CH₃CHO — also written as C₂H₄O . The acetaldehyde molecular weight is 44.05 g·mol⁻¹.

Q: Can acetaldehyde give the Cannizzaro reaction?

No. The Cannizzaro reaction requires an aldehyde with no α-hydrogen — such as formaldehyde or benzaldehyde. Acetaldehyde has three α-hydrogens on the CH₃ group and undergoes aldol condensation instead.

Q: Q4. Does acetaldehyde give the iodoform test?

Yes. Acetaldehyde gives a positive iodoform test — a yellow crystalline precipitate of iodoform (CHI₃) with a characteristic antiseptic odour. This confirms the presence of the CH₃CHO unit , which is essential for the iodoform reaction.

Q: How do you distinguish acetaldehyde from acetone?

Tollens' Test and Fehling's Test both distinguish acetaldehyde from acetone — acetaldehyde gives a silver mirror (Tollens') and a brick-red precipitate (Fehling's), while acetone gives negative results in both. Both give positive Brady's Test and positive Iodoform Test — so neither can be used for this distinction.

Q: Is acetaldehyde a ketone or an aldehyde?

Acetaldehyde is an aldehyde — not a ketone. It contains the –CHO functional group in which the carbonyl carbon is bonded directly to a hydrogen atom. Ketones have two carbon substituents on the carbonyl carbon with no aldehydic hydrogen.

Q: What does acetaldehyde smell like?

The acetaldehyde smell is pungent and fruity — often described as similar to green apples or overripe fruit. It is detectable at concentrations as low as 0.0068 ppm, making it one of the most odour-active aldehydes.

Q: Is acetaldehyde a gas or a liquid at room temperature?

Acetaldehyde is a liquid at room temperature — boiling point 21°C. However, it is extremely volatile — vapours form rapidly in air, and it behaves practically as a gas under warm laboratory conditions.

Q: Which confirmatory test is used for the identification of acetaldehyde?

The confirmatory test for acetaldehyde is the Tollens' Test (silver mirror) — confirming aldehyde character — supported by the Iodoform Test (yellow CHI₃ precipitate) and Legal's Test (red colour), both confirming the CH₃CHO unit specifically.

Q: Why does acetaldehyde give a positive Tollens' test but acetone does not?

Acetaldehyde gives a positive Tollens' test because it contains the –CHO group — the aldehydic hydrogen makes it a reducing agent that reduces Ag⁺ to Ag↓ (silver mirror). Acetone is a ketone with no aldehydic hydrogen — it cannot reduce Tollens' reagent and gives a negative result .

Question 1

What is the IUPAC name of acetaldehyde?

Accepted Answer

The IUPAC name of acetaldehyde is ethanal — derived from the two-carbon chain eth- and the aldehyde suffix -al. Acetaldehyde is the retained common name; ethanal is the preferred systematic name (CAS 75-07-0).

Question 2

What is the molecular formula of acetaldehyde?

Accepted Answer

The acetaldehyde molecular formula is CH₃CHO — also written as C₂H₄O. The acetaldehyde molecular weight is 44.05 g·mol⁻¹.

Question 3

Can acetaldehyde give the Cannizzaro reaction?

Accepted Answer

No. The Cannizzaro reaction requires an aldehyde with no α-hydrogen — such as formaldehyde or benzaldehyde. Acetaldehyde has three α-hydrogens on the CH₃ group and undergoes aldol condensation instead.

Question 4

Q4. Does acetaldehyde give the iodoform test?

Accepted Answer

Yes. Acetaldehyde gives a positive iodoform test — a yellow crystalline precipitate of iodoform (CHI₃) with a characteristic antiseptic odour. This confirms the presence of the CH₃CHO unit, which is essential for the iodoform reaction.

Question 5

How do you distinguish acetaldehyde from acetone?

Accepted Answer

Tollens' Test and Fehling's Test both distinguish acetaldehyde from acetone — acetaldehyde gives a silver mirror (Tollens') and a brick-red precipitate (Fehling's), while acetone gives negative results in both. Both give positive Brady's Test and positive Iodoform Test — so neither can be used for this distinction.

Question 6

Is acetaldehyde a ketone or an aldehyde?

Accepted Answer

Acetaldehyde is an aldehyde — not a ketone. It contains the –CHO functional group in which the carbonyl carbon is bonded directly to a hydrogen atom. Ketones have two carbon substituents on the carbonyl carbon with no aldehydic hydrogen.

Question 7

What does acetaldehyde smell like?

Accepted Answer

The acetaldehyde smell is pungent and fruity — often described as similar to green apples or overripe fruit. It is detectable at concentrations as low as 0.0068 ppm, making it one of the most odour-active aldehydes.

Question 8

Is acetaldehyde a gas or a liquid at room temperature?

Accepted Answer

Acetaldehyde is a liquid at room temperature — boiling point 21°C. However, it is extremely volatile — vapours form rapidly in air, and it behaves practically as a gas under warm laboratory conditions.

Question 9

Which confirmatory test is used for the identification of acetaldehyde?

Accepted Answer

The confirmatory test for acetaldehyde is the Tollens' Test (silver mirror) — confirming aldehyde character — supported by the Iodoform Test (yellow CHI₃ precipitate) and Legal's Test (red colour), both confirming the CH₃CHO unit specifically.

Question 10

Why does acetaldehyde give a positive Tollens' test but acetone does not?

Accepted Answer

Acetaldehyde gives a positive Tollens' test because it contains the –CHO group — the aldehydic hydrogen makes it a reducing agent that reduces Ag⁺ to Ag↓ (silver mirror). Acetone is a ketone with no aldehydic hydrogen — it cannot reduce Tollens' reagent and gives a negative result.

Author: Dr. Shammas Din

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