# [AS Chemistry Help] Struggling to use oxidation states to balanced equations

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#1
Q: Use Oxidation states to balance the following equations:
I) CL2 + NaOH > NaCl03 + NaCl + H20
(the large numbers are supposed to be small)

The answer was: 3CL2 + 6NaOH > NaClO3 + 5NaCl + 3H2O

Can someone explain this?

I did:
Oxidation states:
CL2 = O
NaOH = +1 -2 +1
NaClO3 = +1 +5 -6
NaCl = +1 -1
H2O = +2 -2

So, Cl has lost 4 and Na has gained 1 electron

II)What is the half equations?
0
4 years ago
#2
This is the equation for Cl2 reacting with hot NaOH.
There is either cold NaOH reaction which has CL2 + NaOH= NaClO + NaCl + H2O This has NaClO and not NaClO3
So they gave you a hint in the equation that it is the hot reaction. From there, you have to by heart the equation and numbers 3CL2 + 6NaOH > NaClO3 + 5NaCl + 3H2O
You can specify the change in oxidation states of Chlorine as this is a disproportination reaction. This reaction is not specified in the textbook but is there in the syllabus. So you can say it goes from 0 in Cl2 to -1 (in the NaCl) and from 0 in Cl2 to +5 in NaClO3
2
#3
(Original post by maria.x)
This is the equation for Cl2 reacting with hot NaOH.
There is either cold NaOH reaction which has CL2 + NaOH= NaClO + NaCl + H2O This has NaClO and not NaClO3
So they gave you a hint in the equation that it is the hot reaction. From there, you have to by heart the equation and numbers 3CL2 + 6NaOH > NaClO3 + 5NaCl + 3H2O
You can specify the change in oxidation states of Chlorine as this is a disproportination reaction. This reaction is not specified in the textbook but is there in the syllabus. So you can say it goes from 0 in Cl2 to -1 (in the NaCl) and from 0 in Cl2 to +5 in NaClO3
Thanks, does it really matter if it's hot or cold?
0
4 years ago
#4
It does, Cl2 + 2 NaOH →NaCl + NaClO + H2O
This is Cl2 reacting with cold NaOH, numbers are different and here NaClO is produced and not NaClO3 as I mentioned previously. You have to memorize this too.
Good luck!
0
4 years ago
#5
You do not have to memorise the equations and in fact it is better if you do not as it will mean you have a better understanding of the area.

Cl2 + NaOH --> NaClO3 + NaCl + H2O

In the above equation look at the oxidation state of all the Cl. This is a disproportionation reaction.
The Cl goes from zero in Cl2 to +5 in NaClO3 and from zero to -1 in NaCl. Therefore, the oxidation of Cl required 5 electrons to be lost and the reduction of Cl needed 1 electron to be gained. Since, the number of electrons transferred must be equal, the reduction step must happen 5 times for each time the oxidation step happens. This leads to the following.

Cl2 + NaOH --> NaClO3 + 5NaCl + H2O

Now balance the chlorine and the sodium.

3Cl2 + 6NaOH --> NaClO3 + 5NaCl + H2O

And finally the water

3Cl2 + 6NaOH --> NaClO3 + 5NaCl + 3H2O
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