Question

Question #b0597

Answer 1

Statement number (2) is correct, `H^(+)` can oxidize iron and nickel can reduce `Br_2`.

Standard electrode potentials are used to express the ability of a substance to lose electrons.

When you compare the `E^0` values of two species, keep in mind that a more positive (or less negative) `E^0` will correspond to an oxidizer, and a more negative (or less positive) `E^0` will correspond to a reducer.

Here's a link to a table of Standard Electrode Potentials: http://hyperphysics.phy-astr.gsu.edu/hbase/tables/electpot.html

Any species that appears on the left of the reduction half-reaction will oxidize any species that appears on the right of a reduction half-reaction listed above it in the table.

Likewise, any species that appears on the right of the reduction half-reaction will reduce any species that appears on the left of the reduction half-reaction listed below it in the table.

SIDE NOTE This is true when negative values for `E^0` are listed at the top of the table.

So, starting with the first reaction

• `Br_2` can oxidize `Ni` and `H_2` can reduce `Mn^(2+)`

The reduction half-reactions are

`Br_(2(l)) + 2e^(-) -> 2Br_((aq))^(-)`, `" "E^0 "= +1.07 V"`

`Ni_((aq))^(2+) + 2e^(-) -> Ni_((s))`, `" "E^0 = "-0.23 V"`

Bromine can oxidize nickel because its reduction half-reaction is lower in the table, i.e. it has a more positive `E^0` (+1.07 V compared with -0.23 V).

`2H_((aq))^(+) + 2e^(-) -> H_(2(g))`, `" "E^0 = "0 V"`

`Mn_((aq))^(2+) + 2e^(-) -> Mn_((s))`, `" "E^0 = "-1.18 V"`

Hydrogen gas cannot reduce `Mn^(2+)` because the latter is located above it in the table, i.e. has a more negative `E^0` (-1.18 V compared with 0V).

• `H^(+)` can oxidize `Fe` and `Ni` can reducce `Br_2`

`2H_((aq))^(+) + 2e^(-) -> H_(2(g))`, `" "E^0 = "0 V"`

`Fe_((aq))^(2+) + 2e^(-) -> Fe_((s))`, `" "E^0 = "-0.41 V"`

`H^(+)` can oxidize anything on the right of the reduction half-reaction above it in the table, i.e. that has a more negative `E^0`.

As a result, `H^(+)` can oxidize iron.

The last one will be obvious, since we've already established that bromine can oxidize nickel.

Nickel can reduce bromine because it has a more negative `E^0` value, since it's located above it in the table.