2 Moles: Measuring Matter A UNIT OF MEASURE!!!1 mole = 6.02 x 1023 representative particlesatoms, molecules, formula units, ionsAlso called Avogadro's number
3 Moles Molar mass of compounds – add up parts 1 mole = 6.02 x 1023 particles1 mole is also equal to the molar mass of a substancemolar mass = atomic mass with the units g/mol*g/mol is the same as atomic mass except atomic mass has the units of amuMolar mass of compounds – add up partsFind the molar mass of K2CrO4
16 Moles -2: Mass and the Mole atoms to mass:# particles x mol x # grams6.02 x 1023 particles molHow much mass is in 5.50 x 1022 atoms of helium?
17 mass to atoms:mass x 1 mol x x 1023atoms#grams 1 molHow many atoms of gold in 25.0 g?
18 QUIZ Tomorrow over mole conversions!! Homework 2/9Do problems: 10, 11, 14 & 15QUIZ Tomorrow over mole conversions!!
19 Moles -4: Empirical and Molecular Formulas percent compositionmass of element x 100 = % by massmass of compoundpercent always adds up to 100Find % of H and O in water
20 Moles -4 continuedEmpirical formula – smallest whole # mole ratio of the elements* May or may not be actual molecular formulaTo get:Change g to molGet mole ratioThe ratios are the subscripts*If you are given % composition: assume % is gramsFind the empirical formula of a sample with g S and g O.
21 Moles -4 continuedMolecular formula – specific # of atoms of each element in compoundexperimentally determined molar mass = nmass of empirical formulamultiply n by empirical formula subscriptsmolecular formula = (empirical formula)nProblem: The empirical formula of a substance is CH. The molecular mass of the compound is 78 amu. What is the molecular formula of the compound?
22 EMPIRICAL & MOLECULAR FORMULA PRACTICE Chemical analysis indicates a sample is composed of 40.68% C, 5.08% H and 54.24% O and has a molar mass of g/mol. Determine the empirical and molecular formulas of succinic acid
24 Moles: Moles of Compounds YOU can find moles of a part of a compoundHow many moles of F are in 5.50 moles CCl2F2?* Get ratio from formula.Determine the number of moles of Al ions in 1.25 mol Al2O3
25 Moles -5: The formula for a Hydrate Hydrate – compound with a specific # of water molecules bound to its atomsMethane Hydrate
26 Naming Hydrates Naming: name salt • prefix hydrate CaCl2•2H2O calcium chloride dihydratePrefixes are the same as those used for covalent compoundsAnhydrous – without water used to store water or as drying agentsUsed to store solar energy i.e. sodium sulfate decahydrate
27 Hydrate PracticeWrite the chemical formula of lithium nitrate trihydrate.Write the chemical formula for sodium sulfate decahydrate.What is the molar mass of the hydrate lithium nitrate trihydrate?What is the percent of water in sodium sulfate decahydrate?