Question

1. A student wanted to measure the amounts of (Ca2+) in the human blood. She got 1.00ml which she treated with Na2C2O4 solution. The resulting Ca2C2O4 precipitate was filtered and dissolved in dilute H2SO4 to release C2O42- into solution and allow it to be oxidized. The solution required 2.05ml of 4.88 x 10-4 KMnO4 to reach the endpoint. The balanced equation is:
2KMnO4 + 5Ca2C2O4 + 8H2SO4 ¨ 2MnSO4 + 2K2SO4 + 5CaSO4 + 10CO2 + 8H2O
Write the:
(i) Net ionic equation for this reaction
(ii) Calculate the amount (in mol) of Calcium (Ca2+) used in this reaction.
(iii) Calculate the Calcium ion concentration expressed in units of milligrams (mg) Ca2+/100ml of blood.

Answer 1

i). With a balanced MOLECULAR equation, you should have no trouble writing a net ionic equation.
MnO4^- + C2O4^2- + H^+ ==>Mn^2+ + CO2 + H2O
Just plug in the coefficients.
ii). How many moles MnO4^- were used. moles = M x L = ??
Now use the coefficients in the balanced equation to convert moles MnO4^- to moles C2O4^- and that to moles Ca^+2
iii)grams Ca^2+ = moles Ca^2+ x atomic mass Ca^2+. Convert that to mg and that will be mg Ca^2+ per 1 mL. Multiply by 100 to find mg Ca^2+/100.
Post your work if you get stuck.