1)Write down Mass balance and charge balance equations for 0.100 mol L-1 NaC2O2O

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Explanation / Answer

We have C2O4^2- + MnO4^- ----> CO2? + Mn^2+ C2O4^2- ? 2 CO2 MnO4^- ? Mn^2+ Step 2: Balance all elements other than H and O. C2O4^2- ? 2 CO2 Step 3: Balance the oxygen atoms by adding H2O molecules where needed. MnO4^- ? Mn^2+ + 4 H2O Step 4: Balance the hydrogen atoms by adding H+ ions where needed. 8 H+ + MnO4^- ? Mn^2+ + 4 H2O Step 5: Balance the charge by adding electrons, e-. C2O4^2- ? 2 CO2 + 2 e- 5 e- + 8 H+ + MnO4^- ? Mn^2+ + 4 H2O Step 6: If the number of electrons lost in the oxidation half-reaction is not equal to the number of electrons gained in the reduction half-reaction, multiply one or both of the half- reactions by a number that will make the number of electrons gained equal to the number of electrons lost. Multiply top equation by 5 and bottom equation by 2 to get 10 e- 5 C2O4^2- ? 10 CO2 + 10 e- 10 e- + 16 H+ + 2 MnO4^- ? 2 Mn^2+ + 8 H2O Step 7: Add the 2 half-reactions as if they were mathematical equations. The electrons will always cancel. If the same formulas are found on opposite sides of the half-reactions, you can cancel them. If the same formulas are found on the same side of both half-reactions, combine them. 5 C2O4^2- + 16 H+ + 2 MnO4^- ? 10 CO2 + 2 Mn^2+ + 8 H2O This is the balanced reduction – oxidation equation The coefficients in the balanced equation above indicate ratio of moles of reactants to moles of products. 5 C2O4^2- + 16 H+ + 2 MnO4^- ? 10 CO2 + 2 Mn^2+ + 8 H2O According to the balanced equation, 5 moles of oxalate reacts with 2 moles of permanganate.

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