Question #c40e2

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mrpauller.weebly.com
Oct 18, 2017

Roman numerals are used to indicate the oxidation state of metals which have more than one possible oxidation state.

Explanation:

Here's an example. Copper can form either #Cu^+# or #Cu^(2+)# ions.

So there are actually two different compounds that have the name copper chloride. We need the roman numeral to know which is which. Remember that halogens form ions with a -1 charge. So a chloride ion is #Cl^1#.

#CuCl# has a #Cu^+# so its name is copper(I) chloride

#CuCl_2# has a #Cu^(2+)# so its name is copper(II) chloride

This video includes some more examples...

Hope this helps!

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