markchase1996
markchase1996 6d ago • 0 views

Percent Composition Calculation Examples: Step-by-Step

Hey everyone! 👋 Let's break down percent composition. It might sound scary, but it's actually pretty straightforward once you get the hang of it. I've had so many students ask me about this, so I made this guide to help you ace your next chemistry test! 🧪 Good luck!
🧪 Chemistry

1 Answers

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MrKrabs Jan 5, 2026

📚 Quick Study Guide

  • ⚛️ Percent composition is the percentage by mass of each element in a compound.
  • ➗ To calculate it, use the formula: $\frac{\text{mass of element in 1 mole of compound}}{\text{molar mass of compound}} \times 100$
  • ⚖️ Molar mass is found by adding up the atomic masses of each element in the compound from the periodic table.
  • 🧪 Empirical formulas are the simplest whole number ratio of atoms in a compound, while molecular formulas show the actual number of atoms.
  • 💡 Remember to always include units (grams, g/mol) in your calculations!

🧪 Practice Quiz

  1. Question 1: What is the percent composition of carbon in methane ($CH_4$)?
    1. A) 25%
    2. B) 75%
    3. C) 80%
    4. D) 20%
  2. Question 2: What is the percent composition of oxygen in water ($H_2O$)?
    1. A) 11.1%
    2. B) 88.9%
    3. C) 50%
    4. D) 66.7%
  3. Question 3: What is the percent composition of sodium in sodium chloride ($NaCl$)?
    1. A) 60.7%
    2. B) 39.3%
    3. C) 50%
    4. D) 23%
  4. Question 4: What is the percent composition of hydrogen in glucose ($C_6H_{12}O_6$)?
    1. A) 40%
    2. B) 6.7%
    3. C) 53.3%
    4. D) 50%
  5. Question 5: What is the percent composition of copper in copper(II) sulfate ($CuSO_4$)?
    1. A) 25.4%
    2. B) 39.8%
    3. C) 60.2%
    4. D) 12.7%
  6. Question 6: A compound is found to contain 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen. What is its empirical formula?
    1. A) $CHO$
    2. B) $CH_2O$
    3. C) $C_2H_2O$
    4. D) $C_2HO$
  7. Question 7: What is the percent composition of nitrogen in ammonium nitrate ($NH_4NO_3$)?
    1. A) 17.5%
    2. B) 35%
    3. C) 52.5%
    4. D) 60%
Click to see Answers
  1. Answer: B) 75%
  2. Answer: B) 88.9%
  3. Answer: B) 39.3%
  4. Answer: B) 6.7%
  5. Answer: A) 25.4%
  6. Answer: B) $CH_2O$
  7. Answer: B) 35%

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