1. Law of multiple proportions

2. Different compounds can be composed of the same elemenets. This happens when different compounds containing the same elements have different mass compositions. Ex: – CuCl and CuCl 2 – FeO and Fe 2 O 3 – H 2 O and H 2 O 2

3. The Law of Multiple Proportions The Law of Multiple Proportions states that when different compounds are formed by a combination of the same elements, different masses of one element combine with the same relative mass of the other element in a ratio of small whole numbers. – HUH?!

4. Let’s look at water and hydrogen peroxide Water (H 2 O) and hydrogen peroxide (H 2 O 2 ) are composed of the same elements. We can compare the mass of oxygen in hydrogen peroxide to the mass of oxygen in water. The ratio is 2:1… which means, simply, that H 2 O 2 has 2 times the amount of oxygen than H 2 O.

5. How about comparing compounds of copper and chlorine Copper can combine with chlorine in two different compounds, depending upon conditions under which the reaction took place.

6. Cmpd%Cu%ClMass Cu (g) in 100.0 g of compound Mass Cl (g) in 100 g of compound Mass ratio (Mass Cu Mass Cl) I64.2035.8064.2035.801.793 g Cu/1 g Cl II47.2752.7347.2752.730.8963 g Cu/1 g Cl We can divide the mass ratio of compound I by the mass ratio of compound II to find the ratio between the compounds.

8. Reminders HW due Monday (% comp) No Mid-Term We will be doing a couple of labs next week, starting TUESDAY. Remember to wear APPROPRIATE CLOTHING! Otherwise it is a zero! There may be use of burners and chemicals that could cause injury if not used properly. Remember, it is your responsibility to work safely in the laboratory!