Can you help with Redox titration problems?

Question

THe questions are:
Determine the concentration, Molarity, of Potassium iodide solutionwhere 30.0 mL f the Iodide solution was needed to react completely with 10.0 mL of 0.10M dichromate solution. The balances equation is given below: 3I(-) + Cr2O7(-2) + 14H(+) yields 3I2 + 7H20 +2Cr(+3) and
A 0.0621 M KMnO4 solution was used to titrate a solution containing CaC2O4. If 22.76mL of KMnO4 solution was required to reach the titration endpoint, calculate the number of grams of CaC2O4 in the sample. With the eq: MnO4(-) +C2O4(2-) yields Mn(2+) + CO2

Answer 1

Its just stoichiometry!

First Problem:

0.010 L * 0.10 mol Cr2O7 / L * 3 mol I- / mol Cr2O7 = 0.003 mol I- needed

0.003 mol / 0.030 L = 0.10 M KI


Second Problem:

0.02276 L * 0.0621 mol MnO4 / L * 1 mol C2O4 / mol MnO4 = 0.001413 mol C2O4 present.

MW CaC2O4 = 128 g/mol

0.001413 mol * 128 g/mol = 0.1809 grams CaC2O4

Answer 2

Duluth06 is correct except the first equation is not balanced wrt Iodine.

6I(-) + Cr2O7(-2) + 14H(+) yields 3I2 + 7H20 +2Cr(+3)
Put that in his equation instead of 3I(-) and you then have 0.2M KI solution. Note: this is a 6 electron transfer event.

His second solution agrees with mine.
P.S. Thou shalt AlWAYS balance equations ( the 11th commandment of Chemistry)

Answer 3

for first part answer is 0.1M.For rest