unit 7

Question 1

mole ratios

Answer 1

allows us to convert between the moles of each reactant and products

determined from coefficients in the balanced equation

Question 2

limiting reactant

Answer 2

reactant that is totally consumed when a reaction is completed

limits amount of product that can be formed

Question 3

excess reactant

Answer 3

reactant that remains after the limiting reagent is consumed

Question 4

percent purity (by mass) =

Answer 4

(mass of pure substance / mass of impure sample) x 100%

Question 5

percent yield =

Answer 5

(amount of product obtained / amount of product expected) x 100%

Question 6

theoretical yield defnition

Answer 6

amount of product expected

Question 7

percent composition definition

Answer 7

percent of a compound’s mass that comes from each element

Question 8

how can a compounds theoretical percent composition be calculated?

Answer 8

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%

Question 9

empirical formula definition

Answer 9

chemical formula that shows the simplest ratio of atoms of elements in a compound

Question 10

molecular formula definition

Answer 10

actual number of each type of atom of a compound

Question 11

structural formula defintion

Answer 11

shows the type, number, and arrangement of atoms in a formula, shows how atoms are bonded together

Question 12

structural isomers definition

Answer 12

compounds with the same molecular formula but different structural formulas

Question 13

how to determine empirical formulas from percent composition

Answer 13

1. put percents over 100g of the compound
2. convert the mass of each element
3. divide the numbers of moles for each element by smallest number of moles
4. write formulas based on calculations

Question 14

how to calculate the molecular formula of a compound

Answer 14

1. calculate the empirical formula mass of the compound
2. divide molecular formula mass by the empirical formula mass
3. multiple subscripts by number calculated in step 2 to get formula

Question 15

combustion analysis use

Answer 15

determine the empirical formula of a hydrocarbon

Question 16

combustion reaction products

Answer 16

water and carbon dioxide

Question 17

combustion analysis steps

Answer 17

1. determine masses of C and H in original sample
2. if a 3rd element is present, subtract measured masses of H and C from original sample mass
3. determine moles of C and H (and 3rd element if present) in the original sample
4. find the relative moles of each element by dividing the lowest number to give an empirical formula