UPSC Prelims 1999 · General Studies

Question 128: Science and Technology

Assertion (A): To dilute sulphuric acid, acid is added to water and not water to acid. Reason (R): Specific heat of water is quite large.

aBoth A and R are true, and R is the correct explanation of A

bBoth A and R are true, but R is not a correct explanation of A

cA is true, but R is false

dA is false, but R is true

AnswerThe answer is (a).

Mixing sulphuric acid with water releases a large amount of heat. Adding acid slowly to a large amount of water lets the water, which has a high specific heat, absorb this heat without boiling over. Adding water to concentrated acid can make the first drops boil violently and splash acid. So A is true, R is true, and R explains A. Remember: add acid to water, never the reverse.

A. Acid is added to water, not water to acid, when diluting sulphuric acid.
R. Water has a large specific heat, so it absorbs the heat released.

How you could have got this

If you were sure statement 1 is correct, (d) goes. Then judge the second statement; if it is correct too, decide whether it explains the first.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong

(a) Right. Both are true and the water's large specific heat explains the practice.
(b) Wrong. R does explain A.
(c) Wrong. R is true.
(d) Wrong. A is true.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 1999, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.