How much copper plates onto the nail?
An iron nail in copper sulphate solution turns a copper colour as the iron displaces the copper. In a real lab this takes most of a lesson, and the bench speeds it up and says so. Here the question is how much copper forms. The nail is heavy and the solution is dilute, so this time it is the solution that runs out, and the nail is mostly still there at the end.
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6 steps · Mole Concept · Stoichiometry · Metals and Non-metals
What you will use
Apparatus
- Beaker
Chemicals
- Copper Sulfate Solution
- Iron Nail
The steps
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Pour copper sulphate solution into the beaker, and choose 0.5 M.
Blue: the colour of copper ions in water.
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Drop in an iron nail.
The nail darkens with copper and the blue fades as the copper ions leave the solution.
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How many millimoles of iron is the nail? It weighs 2 g; iron is 55.8 g/mol.
Mass over molar mass.
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Which reagent ran out? Give its formula.
One to one, so it is simply whichever has fewer moles. The nail has far more.
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How many grams of copper formed?
One Cu for each CuSO₄, at 63.5 g/mol.
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How many grams of iron are left?
Most of the nail. Only its surface ever met the copper ions.
What it shows
The heavy nail did not decide how much copper formed. The few millimoles of copper sulphate did. The limiting reagent is often the one you would not guess by looking.