Question

If you mix 3 litres of 0.5M $NaCl$ with 9 litres of 0.2777 M $NaCl$ what will the concentration of the final solution be, assuming that volumes are additive?

• A. 0.33 M
• B. 0.39 M
• C. 0.5777 M
• D. 0.6777 M
• E. None of the above

Answer 1

The correct option is A 0.33 M

Let the concentration of the final solution be $M$

From the equation we know,

$M_1$$V_1$ $+$ $M_2$$V_2$ $=$ ($V_1$ $+$ $V_2$)$M$

Volumes $V_1$ and $V_2$ are additive. $M_1$ and $M_2$ are the molarities of the two solutions of $NaCl$

Thus putting the values of $V_1$ $=$ $3$ liters, $V_2$ $=$ $9$ liters, $M_1$ $=$ $0.5M$, and $M_2$ $=$ $0.2777M$, we get,

($0.5$$\ast$$3$) $+$ ($0.2777$$\ast$$9$) $=$ ($3$ $+$ $9$)$M$

From here, the value of $M$ is obtained as $0.333M$ or $0.33M$

Thus, option $A$ is the correct answer.