View Full Version : chemistry help

2011-03-18, 10:50 AM
oh great minds of the playground, i beseech thee, aid my poor stupid brain. *starts chanting and dancing*

i need to figure out the oxidation number of N in K3Fe(CN)6

i know k is +1 because it's an alkali metal. after that im at a loss

Don Julio Anejo
2011-03-18, 12:40 PM
Fe can be 2+ or 3+, in this case it's 3+ since cyanide is -1 and 6 cyanides are -6.

N is usually -3 unless paired bound to something very electronegative like fluorine or oxygen. In this case it's bound to carbon, which isn't very electronegative.

This makes nitrogen -3 and carbon +2.

2011-03-18, 01:37 PM
Edit: What the person above me said.

2011-03-18, 01:38 PM
how do you know cyanide is -1?

Science Officer
2011-03-18, 01:55 PM
how do you know cyanide is -1?

isn't it sometimes listed as a poly-atomic ion? also HCN is a molecule, so...

EDIT: also, in this case, it wouldn't really work if it was -2 charge or greater (in magnitude).

2011-03-18, 02:05 PM
Cyanide is one of the common polyatomic ions. There's probably a list somewhere in your book of the common ones that they want you to memorize, and this is one of them.

2011-03-18, 02:09 PM
Another way to remember it is that there's a triple bond between Carbon and Nitrogen. That leaves one free "space" on the carbon, so -1.