Question

For the following reaction in acidic solution.

Cr2O7^2- + I- ---> Cr^3+ + IO3-

Give the total balanced net ionic equation.

Answer 1

Break down the equation into reduction and oxidation half equation.

oxidation reaction is

I- --> IO3-

balance the equation starting with oxygen by adding water, then followed by addition of H+ ions to balance H atoms, and then finally the electrons to balance the charges.

You will get something like (for the oxidation);

3H2O + I- --> IO3- + 6H+ + 6e- [6 electrons cancels out the 6+ from H+ leaving a 1- charge from IO3-. This is balanced from the 1- charge by I-]

Do the same with the reduction equation;

Cr2O7^2- --> Cr^3+

when you get both equations balance, cancel out the electrons (you need to manipulate the equation by multiplying each with an integer so that both equations have the same number of electrons). Then add the equations together.

Answer 2

Cr2O7^-2 + I- + 8H^------->2Cr^3+ + IO3^- + 4 H2O