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For 3Ca(OH)2 + 2H3PO4 giving Ca3(PO4)2 + 6H2O, how many moles of Ca(OH)2 react with 1.36 mol of H3PO4?
A2.04 mol
B0.907 mol
C4.08 mol
D1.36 mol
Answer & Solution
Correct answer: A. 2.04 mol
1. The coefficients show 3 mol Ca(OH)2 for every 2 mol H3PO4.
2. The factor needed is 3 mol Ca(OH)2 per 2 mol H3PO4.
3. Multiply: 1.36 mol times 3 divided by 2.
4. That gives 4.08 divided by 2, which equals 2.04 mol Ca(OH)2.
5. Inverting the factor would give 0.907 mol, which is the common slip.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 4 "Stoichiometry of Chemical Reactions", section 4.3 Reaction Stoichiometry_
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