1. Section 6.2 Molar Mass and Percent Composition 1.To understand the definition of molar mass 2.To learn to convert between moles and mass 3.To learn to calculate the mass percent of an element in a compound Objectives

2. Section 6.2 Molar Mass and Percent Composition A. Molar Mass A compound is a collection of atoms bound together. The molar mass of a compound is obtained by summing the masses of the component atoms.

3. Section 6.2 Molar Mass and Percent Composition A. Molar Mass For compounds containing ions the molar mass is obtained by summing the masses of the component ions.

4. Section 6.2 Molar Mass and Percent Composition A. Molar Mass Moles of a compound = Calculations Using Molar Mass Mass of a sample (g) = (moles of sample)(molar mass of compound)

5. Section 6.2 Molar Mass and Percent Composition Objective: 1.Calculate the percent composition of a given compound given the formula or experimental data.

6. Section 6.2 Molar Mass and Percent Composition B. Percent Composition of Compounds *Remember  The law of constant composition Any given compound always contains the same elements in the same proportions by mass For example: Carbon dioxide (CO 2 ) contains: 1- carbon atom 2 – oxygen atoms Always a 2:1 ratio of oxygen:carbon

7. Section 6.2 Molar Mass and Percent Composition B. Percent Composition of Compounds Compounds always have the same # and type of each atoms and also have the same proportions of each element by mass Percentage Composition – mass of each element in a compound relative to the total mass of the compound.

8. Section 6.2 Molar Mass and Percent Composition For example: The Molar mass of carbon dioxide is… C 12.011 g/mol O 15.9994 g/mol 44.010 g/mol What is the percentage of carbon in CO 2 ? What is the percentage of oxygen in CO 2 ?

9. Section 6.2 Molar Mass and Percent Composition Finding Percentage Composition from experimental data A sample of 2.45 g of aluminum oxide decomposes into 1.30 g of aluminum and 1.15 g of oxygen. What is the percentage composition of each element in the compound?

10. Section 6.2 Molar Mass and Percent Composition B. Percent Composition of Compounds Percent composition consists of the mass percent of each element in a compound: Mass percent =