Chapter 15, Problem 48E

The calcium ions in human blood serum are necessary for coagulation (Figure 15.5). Potassium oxalate, K₂C₂O₄, is used as an anticoagulant when a blood sample is drawn for laboratory tests because it removes the calcium as a precipitate of ${\text{CaC}}_{\text{2}}{\text{O}}_{\text{4}}\cdot {\text{H}}_{\text{2}}\text{O}$. It is necessary to remove all but 1.0% of the Ca²+ in serum in order to prevent coagulation. If normal blood serum with a buffered pH of 7.40 contains 9.5 mg of Ca²+ per 100 mL of serum, what mass of K₂C₂O₄ is required to prevent the coagulation of a 10 mL blood sample that is 55% serum by volume? (All volumes are accurate to two significant figures. Note that the volume of serum in a 10-mL blood sample is 5.5 mL. Assume that the K_Sp value for CaC₂O₄ in serum is the same as in water.)

Figure 15.5 Anticoagulants can be added to blood that will combine with the Ca²⁺ ions in blood serum and prevent the blood from clotting. (credit: modification of work by Neeta Lind)