# Titration, finding percentage of compound in unknown substance

mbrauer
Mon, 04/09/2012 - 00:32

A .750 g sample of an uknown solid is dissolved in 100 mL of water and acidified with 25 mL of 3 M H_{2}SO_{4 }then titrated with a .0200 M KMn0_{4} solution. If the unknown solid requires 12.5 mL of the KMnO_{4} solution to reach the endpoint, what is the % sodium oxalate in the unknown solid? Assume the only compound in the unknown solid that reacts with the KMnO_{4} solution is sodium oxalate. Report your answer as a percentage.

Can someone please help?? i can't figure this one out! I'm not even sure where to begin. If someone could explain how to start I think I could figure out the rest.

You need to start with a balanced equation. To check myself, I googled it and found this:

http://www.bgsu.edu/departments/chem/faculty/endres/ch128/oxalate.htm

2 MnO

_{4}- + 16 H^{+}+ 5 C_{2}O_{4}2- -----^{10e}-----> 2 Mn^{+2}+ 8 H_{2}O + 10 CO_{2}(g)Next you need to find the moles of permanganate:

moles of permanganate* = .0125L x .0200 M

Next find the moles of oxalate by using the coefficients in the balanced equation to set up a proportion:

5 moles oxalate / 2 moles permanganate = x moles oxalate / moles of permanganate*

Solve for x moles of oxalate

Now find the mass of the sodium oxalate = moles of oxalate x molar mass of Na2C2O4

% = part / whole x 100 so in this case

% sodium oxalate = mass of sodium oxalate* / .750 g x 100

Hope that helps!