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# AS OCR A Chemistry: How to write the formula of ionic compounds with roman numerals

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1. Hey guys can you explain how to solve this problem? Many thanks.

Q. Write the formula of the sulfate(IV)ion and the chlorate(III)ion
A. SO3^2- and ClO2^-
2. (Original post by thecutiemarshy)
Hey guys can you explain how to solve this problem? Many thanks.

Q. Write the formula of the sulfate(IV)ion and the chlorate(III)ion
A. SO3^2- and ClO2^-
The roman numeral stands for the charge on the positive ion in a compound.

The sulphate (ALWAYS) contains 1 sulphur bonded with 3 oxygens and you are given that the sulphur has a charge of 4+ by the roman numeral, therefore the overall ion must be 2- because the charge on an oxygen ion is always 2- and there are 3 of them. (3x - 2 = -6, -6+4 = -2)

ClO2^-

You are given that the chlorine ion has a charge of +3 by the numeral.
Oxygen always has a charge of -2
So you have -4+3 overall giving -1

Just tag me if you don't understand still
3. Hey thank you for your response!
I understand the first question, but for the second, how is chlorine bonded with 2 oxygen atoms?
Wouldn't it be Cl2O as Cl has -1 charge whilst O has -2 charge.
Sorry we hadn't really covered this in class :s
4. (Original post by thecutiemarshy)
Hey thank you for your response!
I understand the first question, but for the second, how is chlorine bonded with 2 oxygen atoms?
Wouldn't it be Cl2O as Cl has -1 charge whilst O has -2 charge.
Sorry we hadn't really covered this in class :s
Oxygen is always -2 unless in peroxides. If it is chlorate (III) then the oxidation state of chlorine is +3, thus it can be deduced that as an anion, its overall charge must be -1.
5. (Original post by AnIndianGuy)
Oxygen is always -2 unless in peroxides. If it is chlorate (III) then the oxidation state of chlorine is +3, thus it can be deduced that as an anion, its overall charge must be -1.
Hi, I am aware of the oxidation rules but its not addressing the part I dont understand.

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