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Updated Mar 29, 2026

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Mass Calculations Using Balanced Chemical Equations

@sj_hkza

Ever wondered how chemists work out exactly how much product... Show more

# Calculations from Balanced Equations

1) Calculate the mass of hydrogen produced by dissolving 0.2g of magnesium in excess sulphuric acid

Calculating Mass from Balanced Equations - Magnesium Example

When magnesium reacts with sulphuric acid, you can calculate exactly how much hydrogen gas will be produced. The key is following a systematic approach that breaks down the problem into manageable steps.

Start with your balanced equation: Mg + H₂SO₄ → MgSO₄ + H₂. Always check the equation is balanced first - this one already is! Next, identify what you're given (0.2g of magnesium) and what you need to find (mass of hydrogen).

Calculate the moles of magnesium using n = m/GFM. With magnesium's GFM being 24.5, you get n = 0.2/24.5 = 0.008163 mol. The mole ratio from the equation shows 1:1 between Mg and H₂, so you'll also get 0.008163 mol of hydrogen.

Finally, convert moles of hydrogen back to mass using m = n × GFM. With hydrogen's GFM of 2, the answer is 0.008163 × 2 = 0.016g of hydrogen. This step-by-step method works for any similar calculation!

Remember: The mole ratio from your balanced equation is the bridge between reactants and products - it's absolutely crucial for getting the right answer.

Iron Oxide Reduction Calculation

Reducing iron oxide with carbon monoxide is a classic industrial process, and you can calculate the iron yield using the same systematic approach. The balanced equation Fe₂O₃ + 3CO → 3CO + 2Fe shows the stoichiometric relationships you need.

Starting with 6.4g of iron(III) oxide, calculate its moles first. The GFM of Fe₂O₃ is (56×2) + (16×3) = 160, giving you n = 6.4/160 = 0.04 mol of iron oxide.

The mole ratio is crucial here - notice that 1 mole of Fe₂O₃ produces 2 moles of Fe. So 0.04 mol of iron oxide will produce 0.04 × 2 = 0.08 mol of iron. This 1:2 ratio comes directly from the balanced equation.

Convert the moles of iron to mass using iron's GFM of 56: m = 0.08 × 56 = 4.48g of iron. Notice how the mole ratio determines your final answer - getting this step right is essential for exam success.

Top Tip: Always double-check your mole ratios from the balanced equation - they're often where students make mistakes in calculations.

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Chemistry

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Updated Mar 29, 2026

•

2 pages

Mass Calculations Using Balanced Chemical Equations

@sj_hkza

Ever wondered how chemists work out exactly how much product they'll get from a reaction? These calculations help you predict quantities in chemical reactions using balanced equations - a crucial skill for your chemistry exams and practical work.

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Calculating Mass from Balanced Equations - Magnesium Example

Remember: The mole ratio from your balanced equation is the bridge between reactants and products - it's absolutely crucial for getting the right answer.

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Iron Oxide Reduction Calculation

Starting with 6.4g of iron(III) oxide, calculate its moles first. The GFM of Fe₂O₃ is (56×2) + (16×3) = 160, giving you n = 6.4/160 = 0.04 mol of iron oxide.

Top Tip: Always double-check your mole ratios from the balanced equation - they're often where students make mistakes in calculations.