# How do you calculate the relative formula mass of copper oxide using the periodic table?

Jun 28, 2017

It depends on which oxide of copper you want to find.

There are two primary oxides of copper, with copper in the $1 +$ and $2 +$ oxidation states: $\text{Cu"_2"O}$ and $\text{CuO}$.

$\text{Cu"_2"O}$ (copper(I) oxide)

We can use the periodic table, specifically the atomic masses of the elements, to figure out the atomic mass or molar mass of any compound, provided we know the chemical formula. In this problem, we're asked to find the relative formula mass (which is the same thing as the atomic mass).

Finding the atomic mass of a compound is very straightforward; we multiply the atomic mass of each element by how many are in the compound, and do this for each element and sum the total.

The atomic masses of the elements in copper(I) oxide are

• $\text{Cu}$: $63.55$ $\text{amu}$

• $\text{O}$: $16.00$ $\text{amu}$

"formula mass" = (63.55color(white)(l)"amu")(2) + 16.00 $\text{amu}$ = color(red)(143.10 color(red)("amu"

$\text{CuO}$ (copper(II) oxide)

Using the same technique:

$\text{formula mass} = 63.55$ $\text{amu}$ $+ 16.00$ $\text{amu}$ = color(blue)(79.55 color(blue)("amu"