Chemistry question below?

Question

The solubility product constant for Sr(IO3)2 is 1.14 * 10^-7. What volume of 0.0250 M S2O3^2- would be required to tirate a 10.00 mL sample of a saturated solution of Sr(IO3)2?

I got this far: 1 mol of S2O3^2- * 1 mol IO3-/ 6 mol S2O3^2- = mol IO3-

Answer 1

Start with the Strontium side of the problem.
If M moles of Sr(IO3)2 are dissolved in solution,
[M][2M]^2 = 1.14x10-7. Solve for M in moles/liter.

Now you need to figure out the reaction. My guess is the IO3 ion is reduced to I2 and the S2O3 ion is oxidized to SO4=. The final equation will include water and H+.

Once you do that, for every P units of IO3- in the equation, you will have a R units of 2S2O3=.
Then "moles" S2O3= = R/(2P)

Then you do a Moles * Vol = Moles * Vol calculation, or 0.01 * M = 0.025 * V(s2o3) * (R/2P)

Answer 2

You're jumping the gun a little bit in what you're trying to calculate. You want to know how much S2O3 2- solution is necessary to react with a certain amount of IO3-. The first thing you have to do is find out how much that certain amount IS. The way to do that is the following:

The solubility product constant of your salt is 1.14*10^-7, which means that [Sr2+] times [IO3-]^2 equals 1.14*10^-7. Now, however much Sr2+ is in that solution, call it "x", there's going to be twice as much IO3- (2x), because that's what the chemical formula says. Plug these values into your equation and solve for x... then you'll know how much IO3- you need to neutralize.

Next, you can do what you started to do above... translate the number of moles of IO3- that you have into the moles of S2O3 2- you need using the ratio from the balanced equation. Finally, use the molarity of the S2O3 2- solution to convert this to a volume.

Answer 3

Ksp = [reactantA][reactantB] (with coefficients as powers)

Sr(IO3)2 = 1.14 x 10^7

0.0250M = Molar (use stoichiometry to find the volume starting with moles of S2O3 (you multiply the "Molar" by the volume of 0.1L.
When you get that mole value, simply use stoichiometry to find the volume. Use a mol to mol ratio from the equation. :)
S2O3 + Sr(IO3)2 -----> 2S(IO3) + SrO3 :)