MCQ-2 7A

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*Q.69 By increasing temperature of water from 25'C to 100'C then *
A) The pH of water decreases
B) The pOH of water increases
C) The pKw of water remains constant
D) The pH of water remains constant

Correct Ans : A (The pH of water decreases]
Explanation : By increasing temperature the decomposition of water also increases the Kw of water increases approximately 75 times so its mean both [H+] ions and [OH-] ions increases
Kw = [H+] [OH-] or pKw = pH + pOH
Hence we know:
pH = - log [H+]
if [H+] increases then pH decreases however pOH is also decreases because [OH-] ions are also increases.Overall sum of H+ ions and OH- ions increases so Kw increases or pKw decreases.H+ and OH- ions equally increases so water is always neutral at any state.
Remember: by changing temp. Kw,pKw,pH,pOH.H+ and OH- all changes except neutrality of water remains constant.