The aluminum in a 0.767 g sample of an unknown material was precipitated as aluminum hydroxide, Al(OH)3, which was then converted to Al2O3 by heating strongly. If 0.143 g of Al2O3 is obtained from the 0.767 g sample, what is the mass percent of aluminum in the sample? %

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### Problem Statement:
The aluminum in a 0.767 g sample of an unknown material was precipitated as aluminum hydroxide, \( \text{Al(OH)}_3 \), which was then converted to \( \text{Al}_2\text{O}_3 \) by heating strongly. If 0.143 g of \( \text{Al}_2\text{O}_3 \) is obtained from the 0.767 g sample, what is the mass percent of aluminum in the sample?

\[ \boxed{ \ \ } \% \]

### Steps for Solving the Problem:
1. **Calculate the molar masses** of \( \text{Al}_2\text{O}_3 \) and elemental aluminum (Al):
   - Molar mass of \( \text{Al} \) = 26.98 g/mol
   - Molar mass of \( \text{Al}_2\text{O}_3 \):
     \[
     2 \times \text{Al} + 3 \times \text{O} = 2 \times 26.98 \, \text{g/mol} + 3 \times 16.00 \, \text{g/mol} = 101.96 \, \text{g/mol}
     \]

2. **Find the number of moles of \( \text{Al}_2\text{O}_3 \)**:
   \[
   \text{moles of } \text{Al}_2\text{O}_3 = \frac{0.143 \, \text{g}}{101.96 \, \text{g/mol}} \approx 0.001402 \, \text{mol}
   \]

3. **Determine the moles of aluminum in** \( \text{Al}_2\text{O}_3 \):
   \[
   \text{Each mole of } \text{Al}_2\text{O}_3 \text{ contains 2 moles of Al}.
   \]
   \[
   \text{moles of Al} = 2 \times 0.001402 \, \text{mol} = 0.002804 \, \text{mol}
   \]

4. **Calculate the mass of aluminum** in the sample:
   \[
   \text{mass of Al} = 0.
Transcribed Image Text:### Problem Statement: The aluminum in a 0.767 g sample of an unknown material was precipitated as aluminum hydroxide, \( \text{Al(OH)}_3 \), which was then converted to \( \text{Al}_2\text{O}_3 \) by heating strongly. If 0.143 g of \( \text{Al}_2\text{O}_3 \) is obtained from the 0.767 g sample, what is the mass percent of aluminum in the sample? \[ \boxed{ \ \ } \% \] ### Steps for Solving the Problem: 1. **Calculate the molar masses** of \( \text{Al}_2\text{O}_3 \) and elemental aluminum (Al): - Molar mass of \( \text{Al} \) = 26.98 g/mol - Molar mass of \( \text{Al}_2\text{O}_3 \): \[ 2 \times \text{Al} + 3 \times \text{O} = 2 \times 26.98 \, \text{g/mol} + 3 \times 16.00 \, \text{g/mol} = 101.96 \, \text{g/mol} \] 2. **Find the number of moles of \( \text{Al}_2\text{O}_3 \)**: \[ \text{moles of } \text{Al}_2\text{O}_3 = \frac{0.143 \, \text{g}}{101.96 \, \text{g/mol}} \approx 0.001402 \, \text{mol} \] 3. **Determine the moles of aluminum in** \( \text{Al}_2\text{O}_3 \): \[ \text{Each mole of } \text{Al}_2\text{O}_3 \text{ contains 2 moles of Al}. \] \[ \text{moles of Al} = 2 \times 0.001402 \, \text{mol} = 0.002804 \, \text{mol} \] 4. **Calculate the mass of aluminum** in the sample: \[ \text{mass of Al} = 0.
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