Writing chemical formulas

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Katie Clark 3B
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Joined: Fri Sep 25, 2015 3:00 am

Writing chemical formulas

Postby Katie Clark 3B » Wed Nov 18, 2015 11:52 pm

For potassium tetracyanonickelate (II), could someone explain where you incorporate the oxidation number when writing the formula. The answers never include a charge on the coordination complex which confuses me since we often write the names of these complexes and they were given to us with a negative charge on them. If someone could explain how you knew the formula was K2[Ni(CN)4] that would be great.

Franca Park 3J
Posts: 64
Joined: Fri Sep 25, 2015 3:00 am

Re: Writing chemical formulas

Postby Franca Park 3J » Thu Nov 19, 2015 12:02 am

From potassium tetracyanonickelate (II), you know that nickel has a charge of +2. You also know that cyanide has a charge of -1 (from memorization). Since there are 4 cyanides, the charge is -4. Thus the total charge of everything in the brackets is 2+(-4)= -2.

Remember that the metal outside of the brackets, in this case potassium, is used to balance out the charge of everything in the brackets to make the entire complex neutral. potassium is always a +1 charge. Therefore you need 2 potassiums which adds up to a +2 charge to balance the -2 charge inside the brackets.

That is how you get K2[Ni(CN)4]

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