Topic 9C Exercises Question 3

[Vivian Leung 1C]

Hi,

I just needed some clarification on naming potassium hexacyanidochromate (III) to make sure I am doing the problem correctly.

I first looked at the oxidation numbers of each of the atoms and compounds that make up potassium hexacyanido chromate (III).

The oxidation numbers are:
K= +1
CN= -1 (there are 6 of them so -6)
Cr= +3

So the formula based on the name is: K3 [Cr (CN)6].

Am I working through this problem correctly?

[Vivian Leung 1C]

Also, I just assumed that Cr= "+3" but would all metals have a "positive" oxidation number? For instance, would Cobalt (III) always indicate a positive 3 oxidation number for Cobalt or would there be instances that it would indicate a negative 3 oxidation number for Cobalt?

[Pranav Daggubati 3C]

Yes, you are thinking of it in the right way. Also, you could create the transition element ion and then see how many anions are necessary to make it neutral. Most, if not all, of the transition metals form cations.

[Vivian Leung 1C]

Great! Thank you Pranav!

[Jaden Haskins 2E]

Why is there no net negative charge since the compound ends in -ate (chromate)? I thought that if it ended with this suffix then the compound needed to have an overall negative charge.