Question

Magicians often use ‘flash powder’ in their acts. Flash powder contains 69.0% potassium chlorate (31.9% K, 28.9% Cl, 39.2% O) and the remainder is aluminium. Calculate the percentage composition by mass of each element in flash powder

Answer 1

Answer:

$\rm K$: approximately $22.0\%$.

$\rm Cl$: approximately $19.9\%$.

$\rm O$: approximately $27.0\%$.

$\rm Al$: $31.0\%$.

Explanation:

Consider a $100\; \rm g$ sample. There would be $69.0\% \times 100\; \rm g = 69.0\; \rm g$ of $\rm KClO_{3}$ and $100.0\; \rm g - 69.0\; \rm g = 31.0\; \rm g$ of $\rm Al$.

Out of that $69.0\; \rm g$ of $\rm KClO_{3}$:

$31.9\%$ (by mass) would be $\rm K$: $31.9\% \times 69.0\; \rm g \approx 22.0\; \rm g$.

$28.9\%$ (by mass) would be $\rm Cl$: $28.9\% \times 69.0\; \rm g \approx 19.9\; \rm g$.

$39.2\%$ (by mass) would be $\rm O$: $39.2\% \times 69.0\; \rm g \approx 27.0\; \rm g$.

Overall, the composition (by mass) of each element in this mixture would be:

$\rm K$:

$\begin{aligned} & \frac{31.9\% \times 69.0\; \rm g}{100\; \rm g} \\ =\; & 31.9\% \times 69.0\% \\ \approx \; & 22.0\%\end{aligned}$.

$\rm Cl$:

$\begin{aligned} & \frac{28.9\% \times 69.0\; \rm g}{100\; \rm g} \\ =\; & 28.9\% \times 69.0\% \\ \approx \; & 19.9\%\end{aligned}$.

$\rm O$:

$\begin{aligned} & \frac{39.2\% \times 69.0\; \rm g}{100\; \rm g} \\ =\; & 39.2\% \times 69.0\% \\ \approx \; & 27.0\%\end{aligned}$.

$\rm Al$:

$\begin{aligned}& \frac{100\; \rm g - 69.0\; \rm g}{100\; \rm g} \\ =\; & 100\% - 69.0\% \\ =\; & 31.0\%\end{aligned}$.