JEE Main · 2020 · 08 Jan 2020 · Shift 2 · Equilibrium

WhatsApp Email

For the following Assertion and Reason, the correct option is :

Assertion : The pH of water increase with increase in temperature.
Reason : The dissociation of water into

H^{+}

and

OH^{-}

is an exothermic reaction

(A)assertion is not true, but reason is true
(B)both assertion and reason are false✓ Correct
(C)but the reason is not the correct explanation for the assertion
(D)both assertion and reason are true, and the reason is the correct explanation for the assertion

Answer: (B)

Solution

Water's self-ionisation grows with temperature, so

K_{w}

rises as it is heated. Since

[H X^{+}] = [OH X^{-}] = K_{w}

in pure water, a larger

K_{w}

means a larger

[H X^{+}]

and therefore a lower pH, not a higher one, so the assertion is false. The dissociation of water absorbs heat and is endothermic, not exothermic, so the reason is false as well.

JEE Main · 2020 · 08 Jan 2020 · Shift 2 · Single correct option

Practise more: all JEE Main PYQs on Equilibrium →

JEE Main · 2020 · 08 Jan 2020 · Shift 2 · Equilibrium

Solution

More JEE Main questions on Equilibrium