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100 mL of 0.06 M Ca(NO3)2 is mixed with 50 mL of 0.06 M Na2C2O4, after which CaC2O4 precipitates completely. Which of the following statements is correct?

1. 0.003 mol of calcium oxalate is precipitated
2. 0.003 mol of Ca2+ remains in excess
3. Na2C2O4 is the excess reagent
4. The final oxalate ion concentration is 0.003 M

Correct answer: 0.003 mol of calcium oxalate is precipitated

Solution

Oxalate (0.003 mol) is the limiting reagent and reacts 1:1 with Ca2+, so 0.003 mol of CaC2O4 precipitates; 0.003 mol Ca2+ remains in excess.

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