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

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?
(edited 8 years ago)
Reply 1
Avatar for maria.x
maria.x
3
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
Reply 2
Avatar for Dysprosium
Dysprosium
OP
6
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?
Reply 3
Avatar for maria.x
maria.x
3
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!
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
(edited 8 years ago)

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