Question

One litre of $0.15\, M\, Na _{2} SO _{3}$ aqueous solution is mixed with $500\, mL$ of $0.2\, M\, K _{2} Cr _{2} O _{7}$ aqueous solution in acid medium. What is the number of moles of $K _{2} Cr _{2} O _{7}$ remaining in the solution after the reaction?

• A. 0.1
• B. 0.0125
• C. 0.025
• D. 0.05

Answer 1

Answer: (D)

0.05

Answer 2

When $0.15\, M\, Na _{2} CO _{3}$ (1 L) mixed with $0.2\, M$ $K _{2} Cr _{2} O _{7}(5\, L )$ than total molarity $(M) .$ $M =\frac{M_{1} V_{1}+M_{2} V_{2}}{V_{3}}$ $M =\frac{0.15 \times 1+0.2 \times 0.5}{1 .5}$ $M =0.15\, mol / L$ Remaining mole of $K _{2} Cr _{2} O _{7}=0.2-0.15$ $=0.05\, mol / L$