Question

HALF REDOX REACTIONS PLEASE HELP

Answer 1

ok im learning about electrochem right now and the equation is 2Na + 2H20 -> H2 + 2OH- + 2Na^+
how do you break up the equation into oxidation and reduction reactions?
for example, i know oxidation one would be 2Na ->2Na^+ + 2e^-
SO How do you form the reduction one??? please help, thanks

Answer 2

the quick way is to guess by beginning with what's not in the oxidation reaction:

2H20 -> H2 + 2OH-

then balance the charge by adding electrons:

2H20 + 2e -> H2 + 2OH-

so this is a two-electron reduction.

while it is faster, this way of doing things does not illustrate the method that lets us deal with more complicated half-equations.

so let's try it with the slower method: i would try to identify the reduced species by comparing the oxidation numbers. the oxidation number of H in H2O is +1, but it becomes 0 in H2. That is a flashing signal that tells us that the two hydrogen atoms got reduced.

unbalanced: H2O -> H2

how to balance it? in this case, the reaction is in basic conditions (see the OH- on the right). so following the procedure given in a gen-chem book (chemistry:the central sci):

balance the O atoms: H2O -> H2 + H2O
balance the H atoms: H2O (+ 2H^+) -> H2 + H2O
"neutralize" the H+: H2O + 2H+ + 2OH- -> H2 + H2O + 2OH-

so now we have:
3H2O -> H2 + H2O + 2OH-

finally, balance the charge
3H2O + 2e -> H2 + H2O + 2OH-

take one H2O away from both sides, and we end up with the same reduction reaction as we got by guessing.

Answer 3

ok thanks so much!!!!!!!!!!!! :)