EXP 7: WHAT IS THE OXIDATION STATE OF NITROGEN?
What is the oxidation state of the nitrogen in the product when a solution of hydroxylamine hydrochloride is oxidized by acidic iron(III) ion ?
A known amount of hydroxylamine hydrochloride is reacted with ferric ion which is reduced to ferrous ion. Potassium permanganate is used to re-oxidize the ferrous ion back to ferric ion. If the concentration and amount of the permanganate solution are known then the amount of ferrous ion titrated can be calculated. This amount is equal to the amount of ferric ion that originally reacted with the hydroxylamine hydrochloride. The number of electrons transferred as each ferric ion is reduced to ferrous is one, therefore, the total number of electrons lost per hydroxylamine hydroxide can be calculated and the new oxidation state of nitrogen determined.
Caution: All of the solutions in this experiment are skin and eye irritants. The potassium permanganate solution will oxidize skin and clothing. The iron (III) has been acidified with sulfuric acid and the hydroxylamine hydrochloride solution is irritating to skin. Keep them off your skin! Be sure to rinse any spill with water.
ANALYSIS AND RESULTS:
Hydroxylamine hydrochloride, NH20H-HCl, dissolves in water to form hydroxylammonium ion, NH30H1+. Assuming that hydrogen and oxygen have their usual oxidation states, what is the oxidation state of N in NH30H1+?
The NH30H1+ ion is oxidized by the iron(III) ion. You can assume that Fe3+ goes to Fe2+.
To find the oxidation state of nitrogen the key calculation depends on the fact that the total decrease in oxidation state for the iron must equal the total increase for the nitrogen.
Since iron gains one mole of electrons for every mole of iron(III) reduced: (Fe3+ + e- ---> Fe2+), the ratio of moles of NH3OH1+ to moles of iron will be the change in nitrogen's oxidation state.
In this experiment you added an excess of iron (III) solution. You used potassium permanganate solution to determine the moles of Fe2+ present and thus the moles of Fe,3+that reacted. (For every mole of Fe3+ reacted you get one mole of Fe2+.)
The concentrations of your solutions are given in moles/g solution. Multiply the mass of the solution times its concentration to calculate the moles of any reagent used
Be sure to carry out the following calculations and report the answers in your Results and Discussion section (in narrative form): Number each separate calculation.
Adapted from an experiment submitted to Dreyfus 87 by:
Rob Lewis, Downers Grove North H.S., Downers Grove, IL 60615