Molar Masses

Molar Masses

To find the molar mass of an element you must first have a periodic table. You can click here and check out the periodic table page. Save the periodic table there to your computer because trust me you will be using it LOADS!

Getting your calculator is highly recommended at this point if you are just a little slow with the mental maths!

So let’s look at this example to see how we find the atomic mass.

What is the atomic mass of C₂H₄N

1.         separate the elements

C₂

H₄

N

2.         find molar mass of each element

-   now this takes a bit of searching in the periodic table

-   find the element and then look at the number BELOW where it says the atomic mass

-   we round to the nearest tenth in every case apart from Cl, this always stays 35.5

So….

C -> 12

H -> 1

N -> 14

3.         Now you see how next to some elements there is the a little number, this is called the subscript and always comes AFTER the element which it applies to

-   we multiply the subscript by the molar mass of the element

C₂, the subscript is 2 so…12 * 2 = 24

H₄, the subscript is 4 so…1 * 4 = 4

N, no subscript so just 14

4.         Add them all up

24+4+14 = 42

…and that’s your answer. 42!

Yes it’s really really just that easy!

    Try these then scroll down to check answer!

_{1.         1.}           C₂H₄O₂

_{2.         2.}           H₂O

            3.    C₂H₅N_SCl

        _{keep going!}

      ANSWERS!

1.   60

2.   18

3.   110.5

if this is not what you got go back up and see what step you went wrong at!