you often measure the amount of something by 1 of 3 different methods

• count

• mass

• volume

mole - a unit used by chemists that is a specified number of particles → 6.02 × 10 ^ 23

Avogadro’s number - 6.02 × 10 ^ 23

representative particle - refers to the species present in a substance

molar mass - mass of a mole of an element

Avogadro’s hypothesis - equal volumes of gases at the same temp and pressure contain equal numbers of particles

volumes of gases vary with changes in temp and pressure

• T high, V high

• T low, V low

• P high, V low

• P low, V high

22.4 L → molar volume of gas

percent composition - relative amounts of the elements in a compound

empirical formula - basic ratio that gives the lowest whole number ratio if the atoms of the elements in a compound

an empirical formula can differ OR be the same as a molecular formula

• EMP. - HO, H2O2

• MOL. - 1:1, 1:1

FORMULAS:

FINDING THE EMPIRICAL FORMULA

• the percent number x 1 mol / mass of that element

• if not whole numbers, divide by smallest

• if still not whole numbers, multiply by smallest number to get there

PARTICLES TO MOLES

• rep. particles x 1 mol / 6.02 × 10 ^ 23 rep. particles

MOLES TO PARTICLES

• moles x 6.02 × 10 ^ 23 rep. particles / 1 mol

MASS TO PERCENT

• mass of element / mass of compound x 100%

MOLES TO MASS

• moles x mass (g) / 1 mol

MASS TO MOLES

• mass (g) x 1 mol / mass (g)

CALCULATING VOLUME OF GAS AT STP

• moles of gas x 22.4 L / 1 mol

CALCULATING MOLAR MASS OF GAS AT STP

• grams / L x 22.4 L / 1 mol