Balancing Redox Equation

Why do we add h20 to balance the equation when its in aq conditions. And what does it mean that these species h+ or oh- or water, take part in redox reACTion but don't get reduced nor oxidised. :s

Bascically, in a redox reaction or half equation we need to balance the oxygens, hydrogens and cahrges.

You add water to balance the Oxygens first, then H+ ions to balance the hydrogens and then electrons to balance the charges.

e.g. H2SO4 forming SO2
H2SO4 ---> SO2

Left side has more oxygens so we add two waters to the right side:
H2SO4 ---> SO2 + 2H2O

Now we have 4 hydrogens on the right but onl 2 on the left so we balance that:
H2SO4 + 2H+ ---> SO2 + 2H2O

Now you can see that they are all balanced but we still have 2+ charge on the left so to cancel that out we add 2 electrons to the left side as 2-2 = 0:

H2SO4 + 2H+ + 2e- ---> SO2 + 2H2O

Now that is our overall redox equation done.

Just remember the order:

1) Balance oxygens using water
2) Balance hydrogens using H+ ions
3) Balance charges using electrons


Hope this helps

Whilst there is nothing wrong with your method I encourage you to think about it in terms of redox. Note that the oxidation number of sulphur changes from +6 to +4. To be able to do this the sulphur must gain two electrons.

H2SO4 + 2e- ---> SO2

Now add hydrogen ions to balance the charge and finally add water.

I am giving you this explanation because I think it is clearer WHY the number of electrons has to be two in this case rather than just following a stepwise formula.

Bascically, in a redox reaction or half equation we need to balance the oxygens, hydrogens and cahrges.

You add water to balance the Oxygens first, then H+ ions to balance the hydrogens and then electrons to balance the charges.

e.g. H2SO4 forming SO2
H2SO4 ---> SO2

Left side has more oxygens so we add two waters to the right side:
H2SO4 ---> SO2 + 2H2O

Now we have 4 hydrogens on the right but onl 2 on the left so we balance that:
H2SO4 + 2H+ ---> SO2 + 2H2O

Now you can see that they are all balanced but we still have 2+ charge on the left so to cancel that out we add 2 electrons to the left side as 2-2 = 0:

H2SO4 + 2H+ + 2e- ---> SO2 + 2H2O

Now that is our overall redox equation done.

Just remember the order:

1) Balance oxygens using water
2) Balance hydrogens using H+ ions
3) Balance charges using electrons


Hope this helps

Why do we add h20 to balance the equation when its in aq conditions. And what does it mean that these species h+ or oh- or water, take part in redox reACTion but don't get reduced nor oxidised. :s

Gimme a redox equation, ok?

And I'll work through with/for you, step by step

I know how to balance them :s i was asking why we add h2o h+, etc...

I know how to balance them :s i was asking why we add h2o h+, etc...

Because every reaction needs to be balanced and you need the hydrogens and oxygens balanced. I think you cant add just oxygen because that would interfere with the reaction and form something else.

Not sure if thats correct, kinda guessing haha

Because every reaction needs to be balanced and you need the hydrogens and oxygens balanced. I think you cant add just oxygen because that would interfere with the reaction and form something else.

Not sure if thats correct, kinda guessing haha

But this wood only happen in a aq solutions tho :s, but for base solutions u gotta USE OH- to balance :s have you heard about those lol

I think you'll just confuse yourself, just remember the steps and you should be fine, pretty certain you wont be asked why those are used to balance the redox

lol but there's base solution redox hahah XD look at them. Ive confused myself way to much haha XD

This is why I hate chemistry, it confuses so easily haha

are you doing the new spec this year ?

Unfortunately yeah, wby?

yes hows revision going, I've so far done structures, redox, enthalpy, kinetics in depth. periodicity I've done in school etc. But need to do group 2 and 7 and equlibrium to be ready for first paper ahhh XD

I've not really revised in depth at all, I think some time this week im going to dedicate an entire day to chem revision.

Structures and equilibrium Im okay with and we've just recently done group 2 and 7 so I need go over it. If you wanna post any questions like past paper ones please do because it will help me revise too