## Task 1 - 040811

For an experiment, 50 cm³ of 10 percent hydrochloric acid is needed. However, only 36 percent hydrochloric acid is available.

How many cubic centimeters of 36 percent hydrochloric acid must be diluted with distilled water?
Let $x$ be the required amount of 36% hydrochloric acid

$50 \mathrm{~cm}^{3}$ of 10% hydrochloric acid contain $5 \mathrm{~cm}^{3}$ of pure acid $(S)$. Therefore, the following equation can be set up:

$$
S=\frac{36}{100} \cdot x \quad \Rightarrow \quad x=S \cdot \frac{100}{36}=\frac{5 \mathrm{~cm}^{3} \cdot 100}{36}=13 \frac{8}{9} \mathrm{~cm}^{3} \approx 13.9 \mathrm{~cm}^{3}
$$

Thus, approximately $13.9 \mathrm{~cm}^{3}$ of 36% hydrochloric acid and accordingly $50-13.9 \mathrm{~cm}^{3} \approx 36.1 \mathrm{~cm}^{3}$ of distilled water are needed.