Chemistry worksheet for calculating percent composition of elements in various compounds.

Absolutely! I’ll solve each problem step by step, showing you how to calculate the percent composition of each element in a compound.

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🔢 Percent Composition Formula:

> % Element = (Total mass of element in 1 mole of compound / Molar mass of compound) × 100%

We’ll use atomic masses from the periodic table (rounded to two decimal places for accuracy):

- Na = 22.99 g/mol
- Cl = 35.45 g/mol
- Ca = 40.08 g/mol
- N = 14.01 g/mol
- Fe = 55.85 g/mol
- S = 32.07 g/mol
- O = 16.00 g/mol
- K = 39.10 g/mol
- Cr = 52.00 g/mol
- Mn = 54.94 g/mol
- P = 30.97 g/mol

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## ✔ 1. NaCl

Molar mass of NaCl = 22.99 + 35.45 = 58.44 g/mol

a. % of Na = (22.99 / 58.44) × 100% ≈ 39.34%
b. % of Cl = (35.45 / 58.44) × 100% ≈ 60.66%

✔ Answer:
a. 39.34%
b. 60.66%

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## ✔ 2. Ca₃N₂

Molar mass = (3 × 40.08) + (2 × 14.01) = 120.24 + 28.02 = 148.26 g/mol

a. % of Ca = (120.24 / 148.26) × 100% ≈ 81.10%
b. % of N = (28.02 / 148.26) × 100% ≈ 18.90%

✔ Answer:
a. 81.10%
b. 18.90%

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## ✔ 3. Fe₂(SO₄)₃

This is iron(III) sulfate.

First, break down the formula:
- Fe: 2 atoms → 2 × 55.85 = 111.70 g
- S: 3 atoms → 3 × 32.07 = 96.21 g
- O: 12 atoms (because 4 O per SO₄, and 3 SO₄ groups) → 12 × 16.00 = 192.00 g

Molar mass = 111.70 + 96.21 + 192.00 = 399.91 g/mol

a. % of Fe = (111.70 / 399.91) × 100% ≈ 27.93%
b. % of S = (96.21 / 399.91) × 100% ≈ 24.06%
c. % of O = (192.00 / 399.91) × 100% ≈ 48.01%

✔ Answer:
a. 27.93%
b. 24.06%
c. 48.01%

*(Check: 27.93 + 24.06 + 48.01 = 100.00 — perfect!)*

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## ✔ 4. K₂Cr₂O₇

Potassium dichromate.

- K: 2 × 39.10 = 78.20 g
- Cr: 2 × 52.00 = 104.00 g
- O: 7 × 16.00 = 112.00 g

Molar mass = 78.20 + 104.00 + 112.00 = 294.20 g/mol

a. % of K = (78.20 / 294.20) × 100% ≈ 26.58%
b. % of Cr = (104.00 / 294.20) × 100% ≈ 35.35%
c. % of O = (112.00 / 294.20) × 100% ≈ 38.07%

✔ Answer:
a. 26.58%
b. 35.35%
c. 38.07%

*(Check: 26.58 + 35.35 + 38.07 = 100.00 — good!)*

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## ✔ 5. Mn₃P₇

- Mn: 3 × 54.94 = 164.82 g
- P: 7 × 30.97 = 216.79 g

Molar mass = 164.82 + 216.79 = 381.61 g/mol

a. % of Mn = (164.82 / 381.61) × 100% ≈ 43.19%
b. % of P = (216.79 / 381.61) × 100% ≈ 56.81%

✔ Answer:
a. 43.19%
b. 56.81%

*(Check: 43.19 + 56.81 = 100.00 — perfect!)*

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## 📝 Final Answers Summary:

1. NaCl
a. % Na = 39.34%
b. % Cl = 60.66%

2. Ca₃N₂
a. % Ca = 81.10%
b. % N = 18.90%

3. Fe₂(SO₄)₃
a. % Fe = 27.93%
b. % S = 24.06%
c. % O = 48.01%

4. K₂Cr₂O₇
a. % K = 26.58%
b. % Cr = 35.35%
c. % O = 38.07%

5. Mn₃P₇
a. % Mn = 43.19%
b. % P = 56.81%

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Let me know if you want to see the work written out on paper-style or need help with more problems! 😊