Question #b0189

1 Answer
Sep 16, 2017

Answer:

The mass-balance equation is #2["Sr"^"2+"] = 3["PO"_4^"3-"]#.

Explanation:

In a solubility product calculation, a mass-balance equation relates the equilibrium concentrations of the different species in the solution to each another.

For example, assume that you were asked to calculate the molar solubility #s# of strontium phosphate.

You would probably start by writing something like this:

#color(white)(mmmmmm)"Sr"_3("PO"_4)_2"(s)" ⇌ "3Sr"^"2+""(aq)" + "2PO"_4^"3-""(aq)"#
#"E/mol·L"^"-1":color(white)(mmmmmmmmmmll)3scolor(white)(mmmmml)2s#

You are saying that

#["Sr"^"2+"] = 3s# and #["PO"_4^"3-"] = 2s#

Then,

#color(blue)(2["Sr"^"2+"] = 3["PO"_4^"3-"])#

This is the mass-balance equation.

In effect, to get the mass-balance equation, you multiply each concentration by the charge on the ion.