Edexcel AS Chem help: ionic equations

So i have to balance the equation

Cl2 + OH- -> ClO3 + Cl- + H20

Can't you put a 6 in front of OH and a 3 in front of H20???

The answer book states this, but puts a five in front of Cl

Is the book wrong

See page 107 here: http://ashlyns.herts.sch.uk/downloads/learning/A2Chemistry/StudentWorkbook.pdf

You forgot about the oxygen in ClO3. If we put a 6 in front of the OH and a 3 in front of the H2O, the chlorines would be balanced and so would the hydrogens, but we'd have 6 oxygens on the left but 9 on the right.

But wouldn't you have 3 oxygens from ClO3 and the 3 from H2O which makes six??

Sorry, I'm just really confused

I'm an idiot, you're completely right. The equation in the thing you linked is definitely not balanced. What exactly did the task say to do? If it's simply balancing the equation, you're right (I think!).

Nahh you're not! It said you need to balance the equations. But I actually think I'm wrong somehow, because when I typed it into a balancing equation calculator the answer is 3 Cl₂ + 6 OH^{-} = ClO₃^{-} + 5 Cl^{-} + 3 H₂O

Right, I get it now. The problem with your original answer is that whilst the atoms are balanced, the charges aren't. With your first solution, you've got an overall charge of 6- on the left but only 2- on the right. I'm assuming this is the redox chapter? You need to make sure that the electrons are balanced as well as the actual atoms.

Our teacher kind of gave us this work without teaching 'the redox chapter'. Have never heard of that in my life. Should get onto self studying I guess!

Going completely off topic, I was stalking your profile, and WOW YOUR AS LEVELS ARE FANTASTIC You Legend. Any tips?? Especially for maths aha?

If you do self-teach redox, be careful. At least for AQA (the spec I did) it's probably one of the hardest - conceptually - in the book. Redox is normally near the end of the year though which makes me think that maybe I'm overcomplicating this and it's literally just balancing charges.

For someone who got my grades at AS, I've been remarkably silly in this thread! For Maths - past papers. Once you understand the content, just do tons of past papers. In our school, they made us do one a week for each unit (so for further maths, that's 6 1.5hr papers every week by the end of the year) but it's useful because it means you're less likely to get nasty surprises in the exams. Also there are lots of very useful youtube channels if you don't understand things the way your teacher taught you like Maths247 or KhanAcademy.

Thanks for that. Erm so when you balance charges is it basically the case the the overall charge on one side of the equation must equal the overall charge of the other side?

Yes. Because of the law of conservation of charge, charge can never be lost or created. If you've got uneven charges on the left or right, you must be creating or losing protons or electrons which isn't possible (not as far as AS Chemistry is concerned anyway). So the overall charges on the left and right must be equal.

Thank you so much "Sends big hug your way"

Okay, I get what's happened now. This seems to go slightly beyond what is taught in the AQA spec. Using what you learn in the redox chapter, you get to 6Cl2 + 6H2O -> 2ClO3- + 10Cl- + 12H+. According to the internet, this reaction will only occur in a basic solution, i.e. you've got lots of OH- ions everywhere. That means that on the right, 12 OH- ions will react with the 12 H+ ions to give 12H2O, but to balance things we need to add 12 OH- ions to the left hand side. Once you've got that, you simply cancel same things from the left and right and you end up with the correct formula from the calculator.