Section 1: Measuring MatterChapter 7: Chemical Composition

Learning Goals0Explain how a mole is used to

indirectly count the number of particles of matter.

0Relate the mole to a common everyday counting unit.

0Convert between moles and number of representative particles.

Counting Particles0Chemists need a convenient method for accurately counting the number of atoms, molecules, or formula units of a substance.

0The mole is the SI base unit used to measure the amount of a substance.

Counting Particles01 mole is the amount of atoms in 12 g of pure carbon-12, or 6.02 x 1023 representative particles0an atom, a molecule, a formula unit, an electron, an ion, etc.

0The number is called Avogadro’s number.

Counting Particles0This relationship allows us to count atoms by weighing them.

That’s a

lot…

Counting Particles0Twenty-two real copper pennies contain about 1 mol of copper (Cu) atoms.

Counting Particles0Two large helium balloons contain approximately 1 mol of helium (He) atoms.

Converting Between Moles and Particles0Moles to particles:

Converting Between Moles and Particles0Example: How many atoms are in 3.50 mol of He?

Converting Between Moles and Particles0Particles to moles

Converting Between Moles and Particles0Example: If there are 1.1 x 1022 Ag atoms, how many moles of Ag are there?

Practice0Calculate the number of molecules in 11.5 mol of water.

Practice0How many moles are in 5.75 x 1024 atoms of aluminum?

Practice0How many molecules of AgNO3 are there in 3.25 mol of AgNO3? How many atoms are there?