Question

percent composition and molecular formula
quiz complete
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the percent by mass of copper in cubr₂ is
use %element=$\frac{total\\ mass\\ of\\ element\\ in\\ compound}{molar\\ mass\\ of\\ compound}$×100.
28.45%.
44.30%.
63.55%.
71.55%.

Explanation:

Step1: Find molar mass of CuBr₂

Molar mass of Cu = 63.55 g/mol, molar mass of Br = 79.90 g/mol.
$$\text{Molar mass of } \text{CuBr}_2 = 63.55 + 2\times79.90 = 223.35 \text{ g/mol}$$

Step2: Calculate % mass of Cu

Use given percent composition formula.
$$\% \text{Cu} = \frac{63.55}{223.35} \times 100 \approx 28.45\%$$

Answer:

28.45%