CHEM 0010 Unit


UNIT # 7
Introduction
Objectives
Reading
7.1 Calculation of Formula Mass 7.2 Mole Concept 7.3 Atomic Mass Revisited 7.4 Calculation of Molar Mass 7.5 Calculations involving Avogadro # 7.6 Molar Volume of a Gas 7.7 Percent Composition 7.8 Empirical Formula 7.9 Empirical Mass to Molecular Formula
Problems 1 \| 2 \| 3 \| 4 \| 5

CALCULATIONS BASED ON FORMULAE

7.4 - Calculation of Molar Mass

In section 7.1 we learned how to calculate the mass of a formula unit or a molecule. Now we will learn how to calculate the mass of 1 mole of substance. In section 7.3, we saw that the real neat thing about Avogadro's number is that:

We can equate the numerical quantity of mass of a single ATOM (in amu) to the mass of a mole of the same atoms (in grams).

or, when we are talking about molecules,

We can equate the numerical quantity of mass of a single MOLECULE to the mass of a mole of the same molecules (in grams).

For example:

1 water molecule, H₂O

has a mass of 18.015 amu.

2 H atoms:	2 x 1.008 amu = 2.016 amu
1 O atom:	1 x 15.999 amu = 15.999 amu
Total mass:	18.015 amu

2 moles of H atoms:	2 x 1.008 grams = 2.016 grams
1 mole of O atom:	1 x 15.999 grams = 15.999 grams
Total mass:	18.015 grams

1 mole, or 6.022x 10²³, of water molecules has a mass of 18.015 grams.

This is the molar mass of water.

The units of molar mass:

Let's take a look at the determination of the molar mass of sodium carbonate, Na₂CO₃.

Back


All contents copyrighted © 1996-2006 British Columbia Institute of Technology Chemistry Department - 3700 Willingdon Avenue Burnaby, B.C. Canada V5G 3H2