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# Redox Half Equation help please watch

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1. Mn(s)*--> Mn(NO3)2 (aq)

I know Mn = 0 because its elemental.

I am thrown by Mn(NO3)[sub]2[/sub

I thought (NO3) Would be (3 x -2 for oxygen = -6, meaning N =+6) But then I read somewhere that NO3 has a negative charge overall, so Im assuming then N=5?

So, if there is - overall for the Nitrogen Trioxide, does that mean that Mn is +1?

Wait sorry, forgot about the 2

So, does that mean then

Mn = +2

N =+10

O =-12?
2. (Original post by apronedsamurai)
Mn(s)*--> Mn(NO3)2 (aq)

I know Mn = 0 because its elemental.

I am thrown by Mn(NO3)[sub]2[/sub

I thought (NO3) Would be (3 x -2 for oxygen = -6, meaning N =+6) But then I read somewhere that NO3 has a negative charge overall, so Im assuming then N=5?

So, if there is - overall for the Nitrogen Trioxide, does that mean that Mn is +1?

Wait sorry, forgot about the 2

So, does that mean then

Mn = +2

N =+10

O =-12?
Mn is +2 but you won't need to double the oxidation states for nitrogen or multiply by 6 oxygen. They refer to the individual atoms within each molecule: so O is still -2 and N is still +5.
3. (Original post by Roxy1331)
Mn is +2 but you won't need to double the oxidation states for nitrogen or multiply by 6 oxygen. .

Ok...........

What if it was "big" 2 (2 as a coeffecient)
4. (Original post by apronedsamurai)
Ok...........

What if it was "big" 2 (2 as a coeffecient)
Same thing.
5. (Original post by Roxy1331)
Same thing.
Confused again, sorry

NiO2 + 2 H2O + Fe Ni(OH)2 + Fe(OH)2 in basic solution

So can you walk me through the oxidation numbers again please? Will actually paypal you £10

Ni = +4 because O2 =-4?
Im such a ****ing idiot
6. (Original post by apronedsamurai)
Confused again, sorry

NiO2 + 2 H2O + Fe Ni(OH)2 + Fe(OH)2 in basic solution

So can you walk me through the oxidation numbers again please? Will actually paypal you £10

Ni = +4 because O2 =-4?
Im such a ****ing idiot
The oxidation state rules are simple.

1. The sum of all oxidation states = the charge on the species.
2. Oxygen is always -2 except in peroxides (or with fluorine)
3. S block metals are always +1 in compounds
4. Elements are always 0

So yes, in NiO2 nickel is +4
7. (Original post by charco)
The oxidation state rules are simple.

1. The sum of all oxidation states = the charge on the species.
2. Oxygen is always -2 except in peroxides (or with fluorine)
3. S block metals are always +1 in compounds
4. Elements are always 0

So yes, in NiO2 nickel is +4
Next step, balance the oxygens and then the hydrogens, yeah?

2H2O + NiO2 + 4e- ?
8. (Original post by charco)
The oxidation state rules are simple.

1. The sum of all oxidation states = the charge on the species.
2. Oxygen is always -2 except in peroxides (or with fluorine)
3. S block metals are always +1 in compounds
4. Elements are always 0

So yes, in NiO2 nickel is +4
Wait, actually

Fe --> Fe(OH)2 Therefore, = Oxidation of + 2
NiO2 --> NiOH Therefore = Reduction of -2

NiO2 + 2H2O

I get that the oxygens have been balanced here, by virtue of the water molecules. But, what about balancing the hydrogens?

Do I add up all the oxidation numbers?

H2O (So that is +2 and -2) + NiO2 (which is +4 and -4 respectively)

Confused now

2 H 2O + NiO2+2e-

Bit lost where the +2e came from. Is that simply because I have already worked that out, or?
9. (Original post by apronedsamurai)
Wait, actually

Fe --> Fe(OH)2 Therefore, = Oxidation of + 2
NiO2 --> NiOH Therefore = Reduction of -2

NiO2 + 2H2O

I get that the oxygens have been balanced here, by virtue of the water molecules. But, what about balancing the hydrogens?

Do I add up all the oxidation numbers?

H2O (So that is +2 and -2) + NiO2 (which is +4 and -4 respectively)

Confused now

2 H 2O + NiO2+2e-

Bit lost where the +2e came from. Is that simply because I have already worked that out, or?
The key to this question is that it is in alkaline medium so that the only species that you are allowed to add are water molecules and hydroxide ions.

You are told that NiO2 turns to Ni(OH)2

Hence in order to get the hydrogen atoms on the RHS you must add water to LHS

NiO2 + 2H2O --> Ni(OH)2 + 2OH-

You can see that there is more charge on RHS than the LHS by 2 negative.
In order to equalise the charge you must add 2 electrons to LHS

NiO2 + 2H2O + 2e- --> Ni(OH)2 + 2OH-

This is now the first half-equation.

The other species is Fe --> Fe(OH)2

In this case you can use OH- ions to effect the process:

Fe + 2OH- --> Fe(OH)2

Now there is too much charge on LHS so you must add 2 electrons to RHS

Fe + 2OH- --> Fe(OH)2 + 2e-

This is the second half-equation.

Now there are the same number of electrons on the RHS in one half equation and on the LHS in the other, so they can simply be added together.

NiO2 + 2H2O + 2e- --> Ni(OH)2 + 2OH-
Fe + 2OH- --> Fe(OH)2 + 2e-
NiO2 + 2H2O + Fe --> Ni(OH)2 + Fe(OH)2

notice that the hydroxide ions also cancel out in this example.
10. (Original post by charco)
x.

Thank you so much.

See, this is where I am getting tripped up, the rules and limits etc regarding basic solution, acidic solution and alkaline solution

I worked through your stuff though (thanks very much btw, eloquently and clearly written) and I am beginning to see HOW and WHY things fit in the way they do

Some hope for this ****ing retard yet
11. (Original post by apronedsamurai)
Thank you so much.

See, this is where I am getting tripped up, the rules and limits etc regarding basic solution, acidic solution and alkaline solution

I worked through your stuff though (thanks very much btw, eloquently and clearly written) and I am beginning to see HOW and WHY things fit in the way they do

Some hope for this ****ing retard yet
Keep going and ask if in doubt.
12. (Original post by charco)
Keep going and ask if in doubt.
Au + O2 + CN¯ ---> Au(CN)2¯ + H2O2

First I balanced it, ok?

So Au + O2 +2CN- --> Au(CN)-2+H2O2

Then I split the equation to get my two half equations.

2CN- +Au ---> Au(CN)-2 +2e-

Got confused with the reduction equation.

O2 -----> H2O2

RHS has 2 Hydrogens so to balance:

O2 + 2H+ ----> H2O2

Total charge on LHS I thought was 2, (because oxygen here is elemental, ergo, no charge and 2 from the 2 hydrogens I just added) and the RHS was -2 (+2 for the hydrogen, -4 for the oxygen).

Therefore, I would add 4 electrons to LHS?

Ohhhh! Wait! The RHS, that is a peroxide, so it balances out with overall charge of 0?

Ergo, then, that means to make LHS =RHS, we must add 2 electrons not 4 electrons to LHS ?
13. (Original post by apronedsamurai)
Au + O2 + CN¯ ---> Au(CN)2¯ + H2O2

First I balanced it, ok?
No, you should construct the half equations first
14. (Original post by charco)
No, you should construct the half equations first
If it is in acidic conditions we add water or hydrogen

if it is basic conditions we add hydrogen, then hydroxide to balance them into water

Is that correct, or?
15. (Original post by apronedsamurai)
If it is in acidic conditions we add water or hydrogen

if it is basic conditions we add hydrogen, then hydroxide to balance them into water

Is that correct, or?
Acidic use either/both water and hydrogen ions
Basic use either/both water and hydroxide ions
16. (Original post by charco)
Acidic use either/both water and hydrogen ions
Basic use either/both water and hydroxide ions
CO2 ---> CO

I put CO2 ---> CO+H2O +2e

But the answer puts it on the LHS :|

Specifically,

CO2 +H2O +2e- ----> CO +2 OH-

Thought we added water to the oxygen defecient side? So surely that would be RHS, not LHS?
17. (Original post by apronedsamurai)
CO2 ---> CO

I put CO2 ---> CO+H2O +2e

But the answer puts it on the LHS :|

Specifically,

CO2 +H2O +2e- ----> CO +2 OH-

Thought we added water to the oxygen defecient side? So surely that would be RHS, not LHS?
If CO2 turns to CO then you must put in something that absorbs oxygen

In basic medium

CO2 + H2O --> CO + 2OH-

then balance charge

CO2 + H2O + 2e- --> CO + 2OH-

In acidic medium

CO2 + 2H+ --> CO + H2O

then balance charge

CO2 + 2H+ + 2e- --> CO + H2O

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