Everything Science Grade 10

19.1 CHAPTER 19. QUANTITATIVE ASPECTS OF CHEMICAL CHANGE

Element Relative atomic mass (u) Sample mass (g) Number of moles in the sample

Hydrogen 1 , 01 1 , 01

Magnesium 24 , 3 24 , 3

Carbon 12 , 0 24 , 0

Chlorine 35 , 45 70 , 9

Nitrogen 14 , 0 42 , 0

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(1.) 007h (2.) 007i

Molar Mass ESAFY

DEFINITION: Molar mass

Molar mass (M) is the mass of 1 mole of a chemical substance. The unit for

molar mass isgrams per moleor g·mol−^1.

You will remember that when the mass, in grams, of an element is equal to its relative

atomic mass, the sample contains one mole of that element. This mass is called themolar

massof that element.

Note

You may sometimes
see the molar mass
written asMm. We
will use M in this
book, but you should
be aware of the alter-
nate notation.

It is worth remembering the following: On the periodic table, the relative atomic mass that

is shown can be interpreted in two ways.

1. The mass (in grams) of asingle, average atomof that element relative to the mass of

an atom of carbon.

2. The average atomic mass of all the isotopes of that element. This use is therelative

atomic mass.

3. The mass ofone mole of the element. This third use is the molar mass of the element.

334 Chemistry: Chemical change