Transcript Daily Science pg. 73

 How
many atoms are in 3.6 mol of calcium?
 How many moles are in 1.45 x 1024 atoms of
sodium?
 What is the molar mass of K2SO4?
 How many grams of CO are in 2.9 moles?
 How many moles is 236 g of NaOH?
 What is the mass of 7.6 x 1023 atoms of KF?
 How many atoms are in 192 g of MgCl2?
Pg. 73
 Formulas
tell us ratios of the number of
atoms in the compound


Ex. Freon is CCl2F2
There is 1 C, 2 Cl, and 2 F
 We
can figure out how many moles of one
element there are in a given compound.
 Moles of compound x # of atoms of element
1 mole of compound
 How
many moles of F are in 5.50 moles of
CCl2F2?
 Calculate
the number of moles of each
element in 1.25 moles of C6H12O6.
 First,
find the molar mass of the compound
 Multiply the mass of one element by its
subscript
 Divide the mass of one element by the total
mass in the compound
 Multiply by 100
 Ex. H2O
 Determine
the percent by mass of each
element in the compound CaCl2.
 Calculate
the percent composition of each of
the following element in the compound
Ga2(SO4)3 .
 If you have a 100g sample of MgO and 60% is
magnesium and 40% is oxygen, how many
grams of each do you have?
Pg. 75
Empirical formula = the formula with the
smallest whole number ratio of the elements
 If you know the percent composition of the
element, divide the amount of that element by
its molar mass.
 This tells you # moles of that element.
 If it is written as a percent, assume there are
100 g of the compound
 If the numbers aren’t whole numbers, divide by
the smaller value
 If the numbers still aren’t whole numbers,
multiply by the smallest factor that will make
them whole

 Compound
 Determine
with 40.05% S and 59.95% O
the empirical formula for methyl
acetate which has the following chemical
make up: 48.64% C, 8.16% H, and 43.20% O.
 Sometimes
the empirical formula is the same
for two different compounds
 When that happens, you take the
experimentally determined molar mass of
the compound and divide it by the mass of
the empirical formula
 This gives you a whole number (n) that must
be multiplied into the empirical formula
 Succinic
acid is composed of 40.68% C, 5.08%
H and 54.24% oxygen and has a molar mass of
118.1 g/mol. Determine the empirical and
molecular formulas for succinic acid.