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Calculate the resultant pH when 100 mL of an aqueous solution of NaOH having pH = 12 is mixed 300 mL of an aqueous solution of NaOH having pH = 10

Option: 1

10.5


Option: 2

11


Option: 3

11.4


Option: 4

11.8


Answers (1)

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Given pH of solution with 100 ml = 12                \mathrm{\therefore [OH^{-}] = 10^{-2}}

 pH of solution with 300 ml = 10                         \mathrm{\therefore [OH^{-}] = 10^{-4}}

 

After mixing, 

\mathrm{[OH^{-}] = \frac{10^{-2}\times 100}{100+300}+\frac{10^{-4}\times 300}{100+300} = 2.575\times 10^{-3}}

\mathrm{\Rightarrow pOH = -\log(2.575\times 10^{-3}) = 2.6}

\mathrm{\Rightarrow pH = 14-2.6 = 11.4 }

Hence, the correct answer is Option (3)

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