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F325 -balancing

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1. F325 -balancing
hi can someone please show me how to balance this

Zn gives Zn(2+) + e-
Cr2o7(2-) + H+ + e- gives Cr(2+) + H20
the brackets are the charges

ok i know how to balance the first one
you do
Zn gives Zn(+2) + 2e-

then second part i balanced everything except the electron how do u balance the electron they got 8 ? how?
2. Re: F325 -balancing
and should there have to be a 2 in front of cr2o7(2-)?
3. Re: F325 -balancing
Ok, this is how you form and balance half equations:

First off, learn the basic first step. Dichromate ions are reduced to Chromium ions:

Oxygen always comes out as water:

We need more hydrogens on the LHS to balance the equation so add H+:

Now balance the electrons:

Last edited by Dreamweaver; 04-06-2012 at 15:40.
4. Re: F325 -balancing
(Original post by Dreamweaver)
Ok, this is how you form and balance half equations:

First off, learn the basic first step. Dichromate ions are reduced to Chromium ions:

Oxygen always comes out as water:

We need more hydrogens on the LHS to balance the equation so add H+:

Now balance the electrons:

its wrong the electrons has to be 8?
5. Re: F325 -balancing
(Original post by otrivine)
its wrong the electrons has to be 8?
No it's not wrong. If you add up the charges you will find it is:

+6 -> +6

Therefore the charges are balanced.
6. Re: F325 -balancing
(Original post by Dreamweaver)
No it's not wrong. If you add up the charges you will find it is:

+6 -> +6

Therefore the charges are balanced.

mark scheme question 6)b) check
7. Re: F325 -balancing
(Original post by otrivine)

mark scheme question 6)b) check
na what he is saying is right you have 8 electrons for the second equation then u multiply the zinc equation by 4 hence u get 8 electrons i dunno where u got 6, i understand the over equation needs 6 electrons plus 2- from the cr2072- you get 4+ on both sides hence an equal and balanced equation.

check it if u dont believe me.
8. Re: F325 -balancing
(Original post by otrivine)

mark scheme question 6)b) check

(Original post by kurdishboy94)
na what he is saying is right you have 8 electrons for the second equation then u multiply the zinc equation by 4 hence u get 8 electrons i dunno where u got 6, i understand the over equation needs 6 electrons plus 2- from the cr2072- you get 4+ on both sides hence an equal and balanced equation.

check it if u dont believe me.
Both equations are correct. On the MS, the Cr ion has a 2+ charge but in the book you will find examples where Cr is 3+. This is because Cr can have different oxidation states. You need to be careful and always look at the question.

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Last updated: June 4, 2012
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