How much hydrogen does zinc give?
Zinc granules fizz in dilute acid and the gas is hydrogen. This activity weighs the zinc instead of measuring it out of a bottle. Moles of a solid come from its mass and its molar mass, and that is the second of the two ways every mole calculation starts. Then the equation decides which reagent runs out, how much hydrogen that makes, and how much zinc is still in the beaker afterwards.
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6 steps · Mole Concept · Stoichiometry · Metals and Non-metals
What you will use
Apparatus
- Reaction beaker
Chemicals
- Zinc Granules
- Dilute Hydrochloric Acid
The steps
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Drop three zinc granules into the beaker.
Three granules at 0.3 g each is 0.9 g of zinc.
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Pour in dilute hydrochloric acid, and choose 1 M.
Fizzing at the zinc's surface. That gas is hydrogen.
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How many millimoles of zinc went in? Zinc is 65.4 g/mol.
Mass divided by molar mass: the solid's version of volume times strength.
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Which reagent runs out first? Give its formula.
Each zinc needs TWO HCl. Divide each reagent's moles by its number in the equation, and the smaller one runs out.
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What volume of hydrogen is made, in millilitres at RTP?
One H₂ for every two HCl. Then 24 litres for every mole of gas.
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How many grams of zinc are left in the beaker?
What went in, less what the acid could react with, turned back into grams.
What it shows
Whether a reagent is counted from a volume or weighed on a balance, it becomes moles before the equation can use it. From there the answer is always the same two steps: find what runs out, then scale everything else from it.