The two solution of NaOH having molarity $\frac{M}{10}$ and $\frac{M}{30}$ are mixed to prepare 1 L of NaOH solution in such a way that 300 mL of final solution is completely neutralized by $10 mL, 0.5 M H_{3} PO_{4}$ solution.
Calculate the volume of $\frac{M}{10}$ NaOH solution used (in litre).

Question

The two solution of NaOH having molarity $\frac{M}{10}$ and $\frac{M}{30}$ are mixed to prepare 1 L of NaOH solution in such a way that 300 mL of final solution is completely neutralized by $10 mL, 0.5 M H_{3} PO_{4}$ solution.

Calculate the volume of $\frac{M}{10}$ NaOH solution used (in litre).

TestHub · Accepted Answer

H 2 ​ PO 4 ​ + 3 NaOH → Na 3 ​ PO 4 ​ + 3 H 2 ​ O 5 m mol 15 m mol \displaylines 15 = 300 × M M ′ = 20 1 ​ Molarity of NaOH after mixing = 20 1 ​ V 1 ​ + V 2 ​ 10 V 1 ​ ​ + 30 V 2 ​ ​ 3 V 1 ​ + V 2 ​ 3 V 1 ​ + 1000 − V 1 ​ 2 V 1 ​ V 1 ​ ​ = 1000 = 20 1 ​ = 1500 = 1500 = 500 = 250 mL ​

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