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

1 Answer
Dr. K.
Jul 1, 2018

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

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