stoichiometry of redox reactions
I just need someone to check my work. The question was:
Solder is an alloy containing the metals tin and lead. A particular sample of this alloy weighing 1.50 g was dissolved in acid. All the tin was converted to the +2 oxidation state. Next, it was found that 0.368 g of Na2Cr2O7 was required to oxidize the Sn^2+ to Sn^4+ in an acidic solution. In the reaction the chromium was reduced to Cr^3+ ion.
a) Write the balanced net ionic equation for the reaction b/w the Sn^2+ and Cr2O7^2- in an acidic solution.
My answer:
9(Sn^2+ --> Sn^4+ + 2e-)
2(9e- + 14H+ + Cr2O7^2- --> 2Cr^3+ + 7H2O )
----------------------------------------------------------
9Sn^2+ + 18e- + 28H+ + 2Cr2O7^2- --> 9Sn^4+ + 18e- + 4Cr^3+ + 14H2O
cross out the electrons: 9Sn2+ + 28H+ + 2Cr2O7^2- --> 9Sn^4+ + 4Cr^3+ + 14H2O
b) Calculate the number of grams of tin that were in the sample of solder.
Do I have to use the 0.368g of Na2Cr2O7 in order to find the grams of tin? ( using stiochiometry )
Thanks