Question

10. The pharmacist has asked you to weigh out 20 grams of menthol and dissolve it in sterile water to make a 5% solution. Later you are asked to change the concentration to a 1% solution to fill an order that was just received. What will the final volume of a 1% solution be?

Answer 1

We know the formula:

$$\begin{array}{l} \frac{\text{concentration (\%)}}{100\%} \cdot \text{Volume (mL)} = \text{Dosage (gram)} \Rightarrow \\ \Rightarrow \text{Volume (mL)} = \frac{100\% \cdot \text{Dosage (gram)}}{\text{concentration (\%)}} \end{array}$$

So, we will have:

$$\begin{array}{l} \left\{ \begin{array}{l} \text{concentration (\%)} = 1\% \\ \text{Dosage (gram)} = 20 \text{ grams} \end{array} \right. \Rightarrow \\ \Rightarrow \text{Volume (mL)} = \frac{100\% \cdot 20 \text{ grams}}{1\%} = 2000 \text{ mL} = 2 \text{ L}. \end{array}$$

Answer: 2 liters.