Question

The water used in this experiment is sparged with nitrogen to remove any dissolved oxygen. The proton-coupled reduction of oxygen is shown in the following half reaction:

O2 + 4H+ +4e- --> 2H2O

1) Explain why sparging a solution with N2 to remove dissolved oxygen is an equilibrium process.

2) Using the half reaction above, write the balanced equation for the reaction of ascorbic acid with oxygen. Show your work.

3) If you didn’t know whether or not O2 is capable of oxidizing ascorbic acid, how would you determine this by consulting data? What data would you consult and what would you look for?

Answer 1

Sparging & why sparging: In chemistry, sparging also known as gas flushing in metallurgy, is a technique which involves bubbling a chemically inert gas, such as nitrogen, argon, or helium through a liquid. This can be used to remove dissolved gases from the liquid.

When any gas is in contact with water, some gas will be dissolved in wattr. The amount of that dissolves at a particular temparature depends on the pressure, or partial pressure, of the gas. The dissolved gas and undissolved gas are in equilibrium.

For example, lets look at molecular nitrogen in the air, solvated N₂ is in equilibrium with N₂(g) and water. The equilibrium reaction is shown below.

  N₂(aq) <=====> N₂(g) + H₂O

                                         [N₂(g)] [H₂O(liquid)]

                      Keq = ________________________

                                                   [ N₂(aq)]

                                     K_eq                                                              P_N2

K_H   =             ___________________             = ____________________

                              [H₂O(liquid)]                                                [N₂(aq)]

Answer for 2 & 3 :-

Ascorbic acid is classed as reductone. The absobate anion is stabilized by electron delocalization, as shown in terms of resonance between two canonical forms. For this reason ascorbic acid is much more acidic than would be expected if the compound containing only isolated hydroxyl groups.

It is a mild reducing agent and antioxidant. It is oxidized with loss one electron to form a radical cation and then with loss of second electron to form dehydroscorbic acid. It is typicallyreacts with oxidants of the reactive oxygen species, such as hydroxyl radical. Ascorbic acid is special because it can be transfer a single electron, owning to resonance- stabilized nature of its own radical ion called semi dehydroascorbate. The net reaction is ,

RO^. + C6H7O6^- -----> RO^- + C6H7O6 ^. -------> ROH + C66O6.

The oxidized forms of ascarbate are relatively unreactive and do not cause cellular damage.