Unit 4
Mole Concept
Objective: To understand that you can count atoms by weighing atoms and apply that knowledge in a variety of calculations.
3.1 Molecular and Formula Masses
3.2 Percent composition of Compounds
3.4 The Mole and Molar Masses
3.5 Combustion Analysis (empirical and molecular formula)
One very important chemical activity is the synthesis of new substances. Nylon, aspartame (artificial sweetener), Kevlar, and many other materials that make our lives easier and safer all originated in some chemist’s laboratory. Some of the new materials have truly amazing properties. When a chemist makes a new substance, the first order of business is to identify it. What it its composition? What is its chemical formula?
In this chapter we will learn to determine a compound’s formula. Before we can do that, however, we need to think about counting atoms. How do we determine the number of each type of atom in a substance so that we can write its formula? Of course, atoms are too small to count individually. As we will see in this chapter, we typically count atoms by weighing them. So let us first consider the general principle of counting by weighing.
In this unit, make sure that you can say with confidence…
I can…
1. Understand that atoms can be counted by weighing
2. To count an identical number of pieces of any two elements will not require the same weight of each element
3. To calculate the molar mass of a compound
4. To calculate the empirical formula of a compound given mass data
5. To calculate the empirical formula of a compound given % composition data
6. To calculate the molecular formula of a compound given the empirical formula and the molar mass of the full compound
7. To calculate the % composition of a compound given its formula