Section 1: Measuring Matter Chapter 7: Chemical Composition

Learning Goals 0 Explain how a mole is used to indirectly count the number of particles of matter. 0 Relate the mole to a common everyday counting unit. 0 Convert between moles and number of representative particles.

Counting Particles 0 Chemists need a convenient method for accurately counting the number of atoms, molecules, or formula units of a substance. 0 The mole is the SI base unit used to measure the amount of a substance.

Counting Particles 0 1 mole is the amount of atoms in 12 g of pure carbon-12, or 6.02 x representative particles 0 an atom, a molecule, a formula unit, an electron, an ion, etc. 0 The number is called Avogadro’s number.

Counting Particles 0 This relationship allows us to count atoms by weighing them.

Counting Particles 0 Twenty-two real copper pennies contain about 1 mol of copper (Cu) atoms.

Counting Particles 0 Two large helium balloons contain approximately 1 mol of helium (He) atoms.

Converting Between Moles and Particles 0 Moles to particles:

Converting Between Moles and Particles 0 Example: How many atoms are in 3.50 mol of He?

Converting Between Moles and Particles 0 Particles to moles

Converting Between Moles and Particles 0 Example: If there are 1.1 x Ag atoms, how many moles of Ag are there?

Practice 0 Calculate the number of molecules in 11.5 mol of water.

Practice 0 How many moles are in 5.75 x atoms of aluminum?

Practice 0 How many molecules of AgNO 3 are there in 3.25 mol of AgNO 3 ? How many atoms are there?