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Knowing whether the compound has net neutral charge or not

Posted: Tue Dec 02, 2014 6:21 pm
by Alexandra Bowling 1K
For quiz 3 prep #4, you have to find the chemical formula for potassium tetracyanonickelate (II). I know that it should be K2[Ni(CN)4], but why? I know the following:

(CN)4= (-1)x4=-4
Ni (II)=+2

Thus, the charge of the coordination compound is -2, and making potassium K2 instead of K neutralizes the whole compound. But how do you know when you're supposed to neutralize the compound? How can you tell from the formula whether or not the whole compound should have a net negative charge or not?

Re: Knowing whether the compound has net neutral charge or n

Posted: Tue Dec 02, 2014 7:42 pm
by K Honeychurch 1K
I think the problem would have to specify that the compound has a charge, otherwise you can assume the total charge is 0. Also, I don't think we've had a problem in which the compound has a charge.

Re: Knowing whether the compound has net neutral charge or n

Posted: Tue Dec 02, 2014 9:58 pm
by Justin Le 2I
If the compound has a charge, it will say "ion" at the end in the name.

Re: Knowing whether the compound has net neutral charge or n

Posted: Wed Dec 03, 2014 10:39 am
by GinaYoung1L
A coordination compound is always electrically neutral. It includes the complex (metal and ligands inside the brackets) and any outside ions. Therefore, it is not the coordination compound that has the -2 charge, it is the complex. Complexes (only the stuff inside the brackets) can be neutral, anionic, or cationic. It is anionic if there is an -ate attached to the end of the metal's stem name.

Re: Knowing whether the compound has net neutral charge or n

Posted: Wed Dec 03, 2014 12:37 pm
by Alexandra Bowling 1K
But if it does have "ion" at the end of the name, how are you supposed to figure out the positive or negative charge?

Re: Knowing whether the compound has net neutral charge or n

Posted: Wed Dec 03, 2014 9:11 pm
by Valeria Mazzanti 3H
They would probably have to specify the charge it has.

Re: Knowing whether the compound has net neutral charge or n

Posted: Wed Dec 03, 2014 9:21 pm
by thuyphuong1I
If it is an ion, you can usually tell it has a negative charge if "-ate" is added to the end of the metal. You can also determine charge by assigning charges to each element in your complex, given ligands with their prefixes (if any) and the transition metal with its oxidation number, and then adding them up.

Re: Knowing whether the compound has net neutral charge or n

Posted: Wed Dec 03, 2014 9:45 pm
by Justin Le 2I
Gina Young is correct. My previous comment should only apply to complexes.