textbook problem 9C.3a

[Kylie Martin 1G]

Hi, for problem 9C.3a it asks for the formula of potassium hexacyanochromate(III).
The answer is: K3 [Cr(CN)5];

But i do not understand why potassium (K) in the complex formula has a 3, can someone explain? Also, why is the overall net charge 1+ and not 2- as the chromium has charge 3+ and CN has charge 5- ?
thank you

[606373509]

I think you misread the answer. The "hexa" indicates there are 6 CN- in the compound, thus the formula is K3 [Cr(CN)6]. In the complex ion, there's -6 charge from CN- and 3+ charge from Cr(III), making the ion having a -3 charge. Since potassium has +1 charge, there would have to be three potassium in the compound in order to make the overall charge neutral.