Which pair of reagents corresponds to the two calcium precipitation techniques?

• A. Oxalic acid and Chloranilic acid
• B. Oxalic acid and Sodium tartrate
• C. Chloranilic acid and Ammonium oxalate
• D. Oxalic acid and Citrate

Answer: (A)

Calcium can be quantified by two classic precipitation routes: forming an insoluble calcium salt with oxalate and forming an insoluble calcium salt with chloranilate. Oxalic acid provides the oxalate ion needed to precipitate calcium as calcium oxalate, a long-standing gravimetric or turbidimetric approach. Chloranilic acid, on the other hand, forms calcium chloranilate, another precipitate used in calcium determinations. Since these two distinct precipitation reactions define the two techniques, the pair consisting of oxalic acid and chloranilic acid best matches the two calcium precipitation methods. The other options mix reagents that do not correspond to these two established calcium precipitates.