mole ratios
allows us to convert between the moles of each reactant and products
determined from coefficients in the balanced equation
limiting reactant
reactant that is totally consumed when a reaction is completed
limits amount of product that can be formed
excess reactant
reactant that remains after the limiting reagent is consumed
percent purity (by mass) =
(mass of pure substance / mass of impure sample) x 100%
percent yield =
(amount of product obtained / amount of product expected) x 100%
theoretical yield defnition
amount of product expected
percent composition definition
percent of a compound’s mass that comes from each element
how can a compounds theoretical percent composition be calculated?
its chemical formula
-calculate the mass contribution for each element
(moles of element / 1 mol of compound) x (Molar mass of element)
-add the masses to determine the mass of 1 mole of the compound
-divide the mass contribution for each element by the molar mass, multiply by 100%
empirical formula definition
chemical formula that shows the simplest ratio of atoms of elements in a compound
molecular formula definition
actual number of each type of atom of a compound
structural formula defintion
shows the type, number, and arrangement of atoms in a formula, shows how atoms are bonded together
structural isomers definition
compounds with the same molecular formula but different structural formulas
how to determine empirical formulas from percent composition
- put percents over 100g of the compound
- convert the mass of each element
- divide the numbers of moles for each element by smallest number of moles
- write formulas based on calculations
how to calculate the molecular formula of a compound
- calculate the empirical formula mass of the compound
- divide molecular formula mass by the empirical formula mass
- multiple subscripts by number calculated in step 2 to get formula
combustion analysis use
determine the empirical formula of a hydrocarbon
combustion reaction products
water and carbon dioxide
combustion analysis steps
- determine masses of C and H in original sample
- if a 3rd element is present, subtract measured masses of H and C from original sample mass
- determine moles of C and H (and 3rd element if present) in the original sample
- find the relative moles of each element by dividing the lowest number to give an empirical formula
