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.
