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A mixture contains equal numbers of moles of Ca(OH)2 and Al(OH)3. Exactly 0.5 L of 4.0 M HCl is needed to neutralise the entire mixture. What is the total number of moles in the mixture?

1. 0.4 mol
2. 0.5 mol
3. 0.8 mol
4. 1.0 mol

Correct answer: 0.8 mol

Solution

Each pair (Ca(OH)2 + Al(OH)3) consumes 5 mol HCl per mole-pair; 2 mol HCl gives x = 0.4, total = 0.8 mol.

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