What will be the resultant pH when 200 mL of an aqueous solution of HCl ( pH = 2.0 ) is mixed with 300 mL of an aqueous solution of NaOH ( pH = 12.0 )? ( lo g 2 = 0.30 )

Question

TestHub · Accepted Answer

We are given the following solutions:

200 mL of $1 0^{- 2} M (p H = 2.0)$ of HCl

and 300 mL of $1 0^{- 2} M (p H = 12.0)$ of NaOH.

On mixing, 100 mL of $1 0^{- 2} MN a O H$ will be left unneutralized. Since the total volume of the solution would be 500 mL, the concentration of $O H^{-}$ in the solution would be $(1/5) (1 0^{- 2} M) = 2.0 \times 1 0^{- 3} M$ .

Hence,

$pO H = - lo g (\frac{[ O H ^{-} ]}{M}) = - lo g (2.0 \times 1 0^{- 3}) = 2.70$

$p H = 14 - pO H = 14 - 2.70 = 11.30$

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