unit 7 Flashcards
(17 cards)
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