Question

what mass of KCL is dissolved in 250ml of a solution that is 4.00%

Answer 1

For dilute solutions we can assume that solution density is equal to that of water. As the density of water is 1 g/ml, solution mass is 250 g.

$$c _ {\% w / w} = \frac {m (K C l)}{m (\text {solution})} \cdot 100 \%$$

then

$$m (K C l) = \frac {c _ {\% w / w} \cdot m (\text {solution})}{100 \%} = \frac {4.00 \% \cdot 250}{100 \%} = 10 (g)$$

Answer: 10 g.