Empirical and Molecular Formulas

Chemical Formulas tell type & number atoms in compound tell type & number atoms in compound microscopic level: microscopic level: imagine 1 atom, molecule, or formula unitimagine 1 atom, molecule, or formula unit formula indicates atom ratiosformula indicates atom ratios macroscopic level: macroscopic level: imagine working in labimagine working in lab formula indicates mole ratiosformula indicates mole ratios

Formulas ex: 2H 2 O can mean 2 molecules of water2 molecules of water 2 moles of water2 moles of water 2H 2 O molecules contain: 4 H atoms & 2 O atoms 4 H atoms & 2 O atoms 2 moles of H 2 O molecules contain: 4 moles of H atoms & 2 moles of O atoms 4 moles of H atoms & 2 moles of O atoms

What can say about CuSO 4  5H 2 O?

CuSO 4  5H 2 O this is a hydrated salt this is a hydrated salt 1 mole CuSO 4 contains 5 moles water incorporated into its lattice structure1 mole CuSO 4 contains 5 moles water incorporated into its lattice structure heat these salts: heat these salts: water is driven off leaving behind the anhydrous salt (CuSO 4 )water is driven off leaving behind the anhydrous salt (CuSO 4 )

mole ratio in formula can be used to predict how much water found in any size sample mole ratio in formula can be used to predict how much water found in any size sample if had 2 moles of CuSO 4 5 2 O, how much water would you lose on heating? if had 2 moles of CuSO 4 5 2 O, how much water would you lose on heating? ratio of salt to water is:ratio of salt to water is: 1mole salt to 5 moles water 1mole salt to 5 moles water

Empirical Formulas

Empirical Formula smallest whole # ratio of elements in compound smallest whole # ratio of elements in compound Ionic compounds: Ionic compounds: metal & non-metal elementsmetal & non-metal elements only written as empirical formulasonly written as empirical formulas Covalent compounds: Covalent compounds: only non-metal elementsonly non-metal elements written as both empirical AND molecular formulaswritten as both empirical AND molecular formulas molecular formulas = multiples of empirical formulasmolecular formulas = multiples of empirical formulas

Molecular Formulas

gives exact composition of molecule gives exact composition of molecule molecular compounds have both empirical and molecular formulas molecular compounds have both empirical and molecular formulas can be same or differentcan be same or different

Relationship between empirical and molecular formulas molecular formula is whole number multiple of empirical formula molecular formula is whole number multiple of empirical formula molecular formula = n (empirical formula) molecular formula = n (empirical formula) n is small whole number n is small whole number multiplies subscriptsmultiplies subscripts if n = 1 empirical & molecular formulas are the sameif n = 1 empirical & molecular formulas are the same

To Find Molecular Formula If know empirical formula and molar mass, can find molecular formula If know empirical formula and molar mass, can find molecular formula step 1: find mass of empirical formulastep 1: find mass of empirical formula step 2:__molar mass__ = whole number (n)step 2:__molar mass__ = whole number (n) empirical mass empirical mass step 3: multiply subscripts in empirical formula by nstep 3: multiply subscripts in empirical formula by n

Find molecular formula for substance whose empirical formula is CH and whose molar mass is 78.0 g. Find molecular formula for substance whose empirical formula is CH and whose molar mass is 78.0 g. step 1:step 1: empirical mass = 1(12g) + 1(1g) = 13.0 g empirical mass = 1(12g) + 1(1g) = 13.0 g step 2: molar mass = nstep 2: molar mass = n empirical mass empirical mass Step 3: 6 x subscripts in CHStep 3: 6 x subscripts in CH 78.0g = g C6H6C6H6