Question

To prepare a solution that is $0.50$M $KCl$ starting with $100ml$ of $0.40$M $KCl$, we need to :

• A. add $0.75$ g $KCl$
• B. add $20ml$ of water
• C. add $0.10$ mol $KCl$
• D. evaporate $10$ mL water

Answer 1

The correct option is A add $0.75$ g $KCl$

The original solution contains $100$ mL of $0.40M$ $KCl$.

It contains $\frac{100mL}{1000mL}\times 0.40M=0.040moles$ of $KCl$.
$100$ mL of the required solution will contain $\frac{100mL}{1000mL}\times 0.50M=0.050moles$ of $KCl$.

Thus, $0.050-0.040=0.010moles$ of $KCl$ must be added.

This corresponds to $0.010\times (39.1+35.5)$ $=0.76g$ $KCl$.