Homework Help: chemistry

Posted by george on Thursday, November 4, 2010 at 11:49pm.

In the REDOX reaction in basic solution
Zn-->Zn(OH)4+H2
I know that the first half reaction is
4H20+Zn-->Zn(OH)4 +4H+e

but the second one
is either
2e+2H2O--->H2+2OH
(WHICH IS THE ANSWER GIVEN ON THE WORKSHEET)
OR
2e+2H-->H2
I think both leads to the same answer=

2OH+Zn+2H20-->Zn(OH)4 +H2
but I'm not sure if I should add OH instead of H protons since it is a reaction in basic solution.
Someone can help me?

chemistry - DrBob222, Friday, November 5, 2010 at 12:11am
What is the redox equation you are trying to find the half reactions for?

Your entire question is confusing because of the "it might be this, but" and "or it might be this, but..."
If you can clean up the question I can help.
The correct final equation, which you have written as the last step is correct (if you put the charges on).
2H2O + Zn + 2OH^- ==>Zn(OH)4^-2 + H2
In that total redox equation, one half cell is
Zn ==> Zn^+2 + 2e and the other is
2OH^- + 2e + 2H2O ==> H2 + 4OH^-
chemistry - george, Friday, November 5, 2010 at 12:19am
my question is about whether I have to add water or just H to firstly balance the second half reaction

either
2e+2H2O--->H2+2OH

OR
2e+2H-->H2
which one is correct for a basic solution reaction ?
thanks a lot
chemistry - george, Friday, November 5, 2010 at 12:21am
Oh I see you answered that, So , it is incorrect to add 2H to balance H2 in a basic solution... ?

Although all the first steps are the same as used in acidic solution?
chemistry - DrBob222, Friday, November 5, 2010 at 12:29am
In basic solution you add OH^- and not H^+. Either will work; e.g., if adding H^+, then you balance the H^+ added with OH^- and it all comes out in the wash.
However, answer on the worksheet or not, I don't buy that the half cell is
2e + 2H2O ==> H2 + 2OH^-

You didn't say what redox equation you are trying to balance. This one comes from
Zn + OH^- --> Zn(OH)4^-2 + H2 and the two half cells are
Zn ==> Zn^+2 + 2e and
OH^- + ....etc.

The point I'm trying to make is that the H2 gas comes from the base (the OH^- in the initial equation) and not from the H2O which is added as a result of the reaction.
chemistry - Anonymous, Friday, November 5, 2010 at 10:18am
thanks a lot

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