Quantative Chemical Analysis - Ch. 14 Problems

For a particular redox reaction Cr is oxidized to and is reduced to . Complete and balance the equation for this reaction in basic solution. Phases are optional.

In the formula Cr, chromium has an oxidation state of 0, and in , chromium has an oxidation state of 6. Thus, chromium loses 6 electrons in the process.

In going from to , the oxidation state of iron changes from 3 to 2 for a gain of one electron.

To put these two half-reactions together into an overall reaction, we must first multiply the iron reaction by a factor of 6 to balance the electron transfer.

In basic solution, we can add H2O and OH– as needed to balance hydrogen and oxygen*. In the above equation, there are four more oxygen atoms on the right side than the left side, so we should add double that number of OH– ions to the left side.

Now there are eight hydrogen atoms on the left side, so we must add 4H2O on the right to balance hydrogen.

*Another way to balance O and H in basic solution is to first balance as if it were acidic solution, then combine each H with OH– to form water, and add an equal number of OH– ions to other side. Then cancel excess water.!