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JEE Advanced levelSingle correct optionDifficulty 3 of 3ie039

Equal volumes of $NaOH$ solution of pH $12$ and $HCl$ solution of pH $3$ are mixed at 298 K. The pH of the mixture is ( $lo g 4.5 = 0.653$ )

A $7.00$
B $12.35$
C $11.65$
D $11.35$

Answer: C

[OH X^{-}] = 1 0^{- 2}

and

[H X^{+}] = 1 0^{- 3}

before mixing. For one volume each, excess

OH X^{-}

per two volumes

= (1 0^{- 2} - 1 0^{- 3}) /2 = 4.5 \times 1 0^{- 3} M

.

pOH = 3 - 0.653 = 2.347

, so

pH = 11.65

.

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