Question #b0597

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.