Questions: Question 3 (10 points) If one can find the ratio of the number of moles of the elements in a compound to one another, one can find the formula of the compound. In a certain compound of copper and oxygen, CuxOy, we find that a sample weighing 0.7323 g contains 0.6896 g of Cu .

Solution Steps

To find the mass of oxygen in the compound, subtract the mass of copper from the total mass of the sample.

\[ \text{Mass of } \text{O} = 0.7323 \, \text{g} - 0.6896 \, \text{g} = 0.0427 \, \text{g} \]

Use the molar mass of copper (Cu), which is approximately 63.55 g/mol, to calculate the moles of copper.

\[ \text{Moles of Cu} = \frac{0.6896 \, \text{g}}{63.55 \, \text{g/mol}} = 0.01086 \, \text{mol} \]

Use the molar mass of oxygen (O), which is approximately 16.00 g/mol, to calculate the moles of oxygen.

\[ \text{Moles of O} = \frac{0.0427 \, \text{g}}{16.00 \, \text{g/mol}} = 0.002669 \, \text{mol} \]

Divide the moles of each element by the smallest number of moles to find the simplest whole number ratio.

\[ \text{Ratio of Cu} = \frac{0.01086}{0.002669} \approx 4.070 \]

\[ \text{Ratio of O} = \frac{0.002669}{0.002669} = 1 \]

Since the ratio of copper is approximately 4, the empirical formula is \( \text{Cu}_4\text{O} \).

Final Answer