Question

$500$ ml of $2$ M NaCl solution was mixed with $200$ ml of $2$ M NaCl solution. The molarity of NaCl in the final solution is :

• A. 2 M
• B. 3 M
• C. 4 M
• D. 5 M

Answer 1

The correct option is A 2 M

Total volume = 500 ml + 200 ml = 700 ml = 0.7 L.
Number of moles of NaCl in $500$ ml of $2$ M solution $=$ $2\times \frac{500ml}{1000ml}=1$ mole.
Number of moles of NaCl in $200$ ml of $2$ M solution $=$ $2\times \frac{200ml}{1000ml}=0.4$ mole.
Total number of moles of NaCl $=1+0.4=1.4moles$.
Molarity of the resulting solution $M=\frac{1.4moles}{0.7L}=2M$.

Therefore, the option is A.