Question

How do you calculate the relative formula mass (M) of calcium carbonate? Relative atomic masses C = 12, O = 16, Ca = 40?

Answer 1

100

Explanation:

To calculate the relative formula mass of calcium carbonate, we first need to write out its formula. It's an ionic compound formed between calcium ion `(Ca^"2+")` and carbonate ion `(CO_3^"2-")`.

There are several ways to figure out the formula, one of the easier way is using the cross-over method. You may watch it here:
How to Write formula for Ionic Compound

After crossing over the number of the charges in `Ca^"2+"` and carbonate ion `CO_3^"2-"`, we'll get `Ca_2(CO_3)_2`, which can be further simplified into `CaCO_3`.

To calculate the relative formula mass, we'll need to count the number of atoms that are present in `CaCO_3`.
How to Count Atoms

In `CaCO_3`, we have
1 Ca
1 C
3 O

And then, we multiply with its atomic mass and add them all up, like this,

Relative formula mass `CaCO_3` = (1 x 40) + (1 x 12) + (3 x 16) = 100