Question

What is the formula for cupric cyanide?

Answer 1

The formula for cupric cyanide is `"Cu(CN)"_2"`.

Explanation:

The cupric ion (from the latin "cuprum", corresponding to `"Cu"`) is the copper(II) ion, with a charge of `2^+`, because the "-ic" ending implies the higher of two oxidation states (`+1,+2`), as opposed to "cuprous". Its symbol is therefore `"Cu"^(2+)`.

The cyanide ion has a charge of `1^-`, and its formula is `"CN"^(-)`.

All ionic compounds' charges must add up to the net charge, so the number of positive ions and negative ions must be such that the total positive charge plus the total negative charge equals the net charge.

Since the cupric ion has a charge of `2^+`, and the cyanide ion has a charge of `1^(-)`, there must be two cyanide ions for every cupric ion.

Therefore, the formula for cupric cyanide contains one cupric ion and two cyanide ions, and the formula is `"Cu(CN)"_2"`. This compound is also called copper(II) cyanide.

`"Cu"^(2+) + "2CN"^(-)` `rarr` `"Cu(CN)"_2`