Question

How do you determine the formula and molar mass of silver cyanide?

Answer 1

Identify the bond and participating atoms.

Add the atomic mass of all elements present.

Explanation:

Formula

You must identify the type of bond(s) present. In this case, it is an ionic compound.

You must also identify the elements/polyatomic ions present. In this case, there is silver (`Ag`), and cyanide (`CN`).
- If there was a multivalent element, you have to look at the chemical name. If there are Roman numerals, then the preceding element is multivalent with a charge of whatever the numerals indicate. E.g. `CuSO_"4"` = Copper (II) sulfate -> the subscripts were reduced.

Knowing that it is an ionic compound, we know that the electrons are transferred. Thus the cation goes first (`Ag`), then the anion (`CN`). The charges are `1+` and `1-`, therefore we do not need to reduce.

We get `AgCN`.

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Molar mass

You need a periodic table for this. The molar mass of a compound is simply the sum of all elements in the compound (including the subscripts if any; no coefficients if any).

`Ag` has a atomic mass of `107.87 mu`
`C` has a atomic mass of `12.01 mu`
`N` has a atomic mass of `14.01 mu`

Add them all up and you get `133.89 g/(mol)`. There is a reason why the units for atomic mass and molar mass are different. Once you learn about mols and such, you will know why, so I will leave that to your teacher.

Hope this helps :)