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JEE Advanced levelSingle correct optionDifficulty 3 of 3ie096

Equal volumes of an $HCl$ solution of pH 2.00 and a $NaOH$ solution of unknown pH are mixed, and the resulting solution has pH 3.00 at 298 K. The pH of the $NaOH$ solution is nearest to (use $lo g 2 = 0.301$ )

A $12.00$
B $11.00$
C $12.30$
D $11.90$

Answer: D

Let each volume be

V

and

[NaOH] = c

. Excess

H X^{+}

= (0.01 - c) V

in volume

2 V

equals

1 0^{- 3}

:

0.01 - c = 0.002

, so

c = 0.008 M

.

pOH = 3 - 3 lo g 2 = 3 - 0.903 = 2.097

, so

pH = 11.90

.

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