1.Consider the balanced synthesis of water: 2 H₂ + O₂ -> 2 H₂O. How many moles of H₂O are produced when 4.0 moles of O₂ react completely with excess hydrogen gas?
A2.0 moles H₂O
B4.0 moles H₂O
C8.0 moles H₂O
D16.0 moles H₂O
Grade 10physical scienceOriginal practice
High School Chemistry: Stoichiometry & Mole Ratio Calculations
Calculate molar masses, convert between grams and moles, balance chemical equations, and determine limiting reactants with step-by-step solutions.
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About this practice
Grade 10 · science · Matching answer key included · US Letter and A4
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Teaching guide, sample answers and curriculum references
Before you begin
Balance a chemical equation and convert mass to moles using molar mass.
How to use this worksheet
- Model the target skill: use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction. Use the first task as a guided example before asking for an independent response.
- Check readiness first: Balance a chemical equation and convert mass to moles using molar mass.
- Discuss an incorrect response using this distinction: Equation coefficients compare moles, not masses; a gram-to-gram conversion needs molar masses.
A common mistake to discuss
Equation coefficients compare moles, not masses; a gram-to-gram conversion needs molar masses.
What to practice next
Write units beside every conversion and check which reactant limits the process.
Sample question and answer
Consider the balanced synthesis of water: 2 H₂ + O₂ -> 2 H₂O. How many moles of H₂O are produced when 4.0 moles of O₂ react completely with excess hydrogen gas?
- A. 2.0 moles H₂O
- B. 4.0 moles H₂O
- C. 8.0 moles H₂O
- D. 16.0 moles H₂O
Answer: C. From the balanced coefficients, the mole ratio of H₂O produced to O₂ consumed is 2 mol H₂O / 1 mol O₂. Therefore: 4.0 mol O₂ × (2 mol H₂O / 1 mol O₂) = 8.0 moles H₂O.
Intended curriculum references: NGSS.HS-PS1-7. These references describe learning goals; they are not endorsements.
Published 2026-10-02; updated 2026-10-02. Original MakeWorksheet practice. Automated consistency checks support publication; independent subject-specialist review is not recorded. Read our editorial policy.
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