Assertion (A) : Ethanoic acid is also known as glacial acetic acid. Reason (R) : The melting point of pure ethanoic acid is 290 K and hence it often freezes during winters in cold climates.

Carbon and its Compounds

Properties of Ethanoic Acid

Options

(a)Both (A) and (R) are true and (R) is correct explanation of the assertion.

(b)Both (A) and (R) are true but (R) is not the correct explanation of the assertion.

(c)(A) is true but (R) is false.

(d)(A) is false but (R) is true.

Official Answer

Both (A) and (R) are true and (R) is the correct explanation of the assertion.

glacial acetic acidmelting point 290 Kfreezes during winterscorrect explanation

Marking Scheme

1Identify that Assertion (A) is true. (0.25 marks)
2Identify that Reason (R) is true and contains the correct melting point of $290\text{ K}$ . (0.25 marks)
3Establish the logical link that freezing in cold climates gives it a glacier-like appearance, explaining the name 'glacial acetic acid'. (0.5 marks)

Hint

Convert $290\text{ K}$ to Celsius ( $290 - 273 = 17^\circ\text{C}$ ) and think about how this relates to room temperature in cold climates and the term 'glacial'.

Quick Oral Answer

Pure ethanoic acid has a melting point of $290\text{ K}$ or $17^\circ\text{C}$ . In cold climates, the temperature often drops below this, causing the acid to freeze into ice-like crystals that look like glaciers. Hence, it is called glacial acetic acid.

Analysis & Explanation

Assertion (A) is true because ethanoic acid is commonly known as acetic acid, and in its pure, water-free form, it is called 'glacial acetic acid'. Reason (R) is also true because the melting point of pure ethanoic acid is $290\text{ K}$ (which is $17^\circ\text{C}$ ). Since this temperature is close to or above typical winter temperatures in cold climates, pure ethanoic acid readily freezes into ice-like crystals. This glacier-like appearance of the frozen acid is precisely why it is named 'glacial acetic acid'. Thus, the reason correctly explains why it is called glacial acetic acid.

Common Mistakes

1Students often fail to connect the physical state (freezing/glacier-like crystals) with the term 'glacial', choosing option (b) instead of (a).
2Confusing the melting point of ethanoic acid with its boiling point.

Interesting Facts

Glacial acetic acid is anhydrous (contains less than 1% water). If water is added, its freezing point drops significantly due to freezing-point depression, meaning it won't freeze as easily in winter!

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2020?

This question carries 1 mark in the CBSE Class 10 Science 2020 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Carbon and its Compounds" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Properties of Ethanoic Acid" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2020 paper?

This is a MCQ question from Section A in the CBSE Class 10 Science 2020 paper.