Formula Mass

• Formula mass: sum of the atomic masses of the atoms in the chemical formula

The Mole

• The mole is used to count atoms and molecules in samples

• One mole: the amount of substance that contains as many atoms, molecules, or other objects, as the number of atoms in 12 grams of isotopically-pure 12C

• Avogadro’s number: 6.022 x 10^23

• One mole of any atom, ion or molecule contains 6.022 x 1023 of said object

Percentage Composition

• Percentage composition: percentage, by mass, contributed by each element

Empirical Formulas

• Derived from experimental data (the percentage composition)

• Empirical formulas: give relative number of atoms of each element in a substance

• Molecular formulas: give actual number of atoms in a substance

• e.g., H2O2 Molecular formula; HO Empirical formula

Solution

• Solution: a homogeneous mixture of two or more substances

• Solvent: the substance present in greatest quantity

• Solutes: dissolved in the solvent

• Molarity (M) = (moles of solute) / (volume of solution in liters)

PPM (parts per million) and PPB (parts per billion)

• ppm = mass of solute/mass of solution x 10^6

• ppb = mass of solute/mass of solution x 10^9

• ( 1 ppm = 1000 ppb)