Solutions to a percent composition worksheet, listing the percentage of each element in the given compounds.

The image you've uploaded is a Percent Composition Worksheet - Solutions, which provides the percent composition of elements in several compounds. Let's go through each compound, verify the solutions, and explain how to calculate percent composition step by step.

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🔷 What is Percent Composition?

The percent composition of an element in a compound is the percentage by mass that the element contributes to the total mass of the compound. It’s calculated using:

\[
\text{Percent Composition} = \left( \frac{\text{Total mass of element in one mole of compound}}{\text{Molar mass of compound}} \right) \times 100\%
\]

We’ll use atomic masses from the periodic table (rounded to one decimal place):

- Cu: 63.5 g/mol
- Br: 79.9 g/mol
- Na: 23.0 g/mol
- O: 16.0 g/mol
- H: 1.0 g/mol
- N: 14.0 g/mol
- S: 32.1 g/mol

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✔ Problem 1: CuBr₂

Step 1: Molar Mass
- Cu: 63.5 g/mol
- Br₂: 2 × 79.9 = 159.8 g/mol
- Total = 63.5 + 159.8 = 223.3 g/mol

Step 2: Percent Composition
- Cu:
\[
\frac{63.5}{223.3} \times 100\% \approx 28.4\%
\]
- Br:
\[
\frac{159.8}{223.3} \times 100\% \approx 71.6\%
\]

✔ Matches the given answer.

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✔ Problem 2: NaOH

Step 1: Molar Mass
- Na: 23.0
- O: 16.0
- H: 1.0
- Total = 23.0 + 16.0 + 1.0 = 40.0 g/mol

Step 2: Percent Composition
- Na:
\[
\frac{23.0}{40.0} \times 100\% = 57.5\%
\]
- O:
\[
\frac{16.0}{40.0} \times 100\% = 40.0\%
\]
- H:
\[
\frac{1.0}{40.0} \times 100\% = 2.5\%
\]

✔ Matches the given answer.

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✔ Problem 3: (NH₄)₂S

This compound has:
- 2 nitrogen atoms
- 8 hydrogen atoms (since NH₄⁺ has 4 H, and there are two)
- 1 sulfur atom

Step 1: Molar Mass
- N: 2 × 14.0 = 28.0
- H: 8 × 1.0 = 8.0
- S: 32.1
- Total = 28.0 + 8.0 + 32.1 = 68.1 g/mol

Step 2: Percent Composition
- N:
\[
\frac{28.0}{68.1} \times 100\% \approx 41.1\%
\]
- H:
\[
\frac{8.0}{68.1} \times 100\% \approx 11.8\%
\]
- S:
\[
\frac{32.1}{68.1} \times 100\% \approx 47.1\%
\]

✔ Matches the given answer.

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✔ Problem 4: N₂S₂

Step 1: Molar Mass
- N: 2 × 14.0 = 28.0
- S: 2 × 32.1 = 64.2
- Total = 28.0 + 64.2 = 92.2 g/mol

Step 2: Percent Composition
- N:
\[
\frac{28.0}{92.2} \times 100\% \approx 30.4\%
\]
- S:
\[
\frac{64.2}{92.2} \times 100\% \approx 69.6\%
\]

✔ Matches the given answer.

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✔ Final Summary

| Compound | Element | Percent Composition |
|--------|--------|---------------------|
| CuBr₂ | Cu | 28.4% |
| | Br | 71.6% |
| NaOH | Na | 57.5% |
| | O | 40.0% |
| | H | 2.5% |
| (NH₄)₂S | N | 41.1% |
| | H | 11.8% |
| | S | 47.1% |
| N₂S₂ | N | 30.4% |
| | S | 69.6% |

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📌 Conclusion

All the percent compositions provided in the worksheet are correct and match the calculations based on molar masses and atomic weights.

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