Human bodies maintain their balance (homeostasis) through a series of equilibria. An important equilibrium

Question

involves calcium ion because Ca2+ is important for muscle contractions in the heart as well as for strong bones.
Bone is a complex tissue consisting of living cells and non-living material. Calcium phosphate is part of the
non-living material and is how the body stores calcium.
a) Write the solubility product expression for the dissolution of calcium phosphate.
b) Assume all available bone material is pure calcium phosphate with a density of 3.14 g/mL. When blood
calcium ion concentration decreases, a hormone is released that causes calcium ions from the bones to be
released into the bloodstream. What effect does this have on the density of calcium phosphate in the bones?
Explain your answer.
Equations for parts (c) and (d) below.
H3PO4 + H2O ⇄ H3O1+ + H2PO41- Ka1 = 7.5 × 10-3
H2PO41- + H2O ⇄ H3O1+ + HPO42- Ka2 = 6.2 × 10-8
HPO42- + H2O ⇄ H3O1+ + PO43- Ka3 = 4.8 × 10-13
c) Blood pH is approximately 7.4 in healthy people. What are the predominant forms of phosphate in the blood at
this pH? Justify your answer.
d) Again, assume all available bone material is pure calcium phosphate. One way skeletons can be cleaned for
study is to boil the bones in a solution to remove all extraneous material, leaving just the pure bone. Based on
the equilibrium equations above and also the solubility product expression you derived in (a), would a highly
acidic or highly basic solution be best to clean the bones? Explain your answer.