AP Chemistry Unit 1 Study Guide

What is Avogadro’s number, and why is it important in chemistry?

Avogadro’s number is 6.022 \times 10^{23}\text{ mol}^{-1}. It represents the number of particles (atoms, molecules, or formula units) in one mole of a substance, allowing chemists to count particles by weighing samples.

How many molecules are in 2.00 moles of water (H₂O)?

Number of molecules = 2.00\text{ mol} \times (6.022 \times 10^{23}\text{ molecules/mol}) = 1.20 \times 10^{24}\text{ molecules}

What is the mass (in grams) of one mole of carbon dioxide (CO₂)?

The mass of one mole of CO_2 is the molar mass: 12.0\text{ g/mol (C)} + 2 \times 16.0\text{ g/mol (O)} = 44.0\text{ g/mol}

If you have 18.0 grams of water (H₂O), how many moles do you have? (Molar mass of H₂O = 18.0 g/mol)

n = m/M = 18.0\text{ g} / 18.0\text{ g/mol} = 1.00\text{ mol}