Proportions/Rates/Fractions

1,500 pages in 12 days  =  ______   pages in 3 days

18 calls in 6 hours  =  ______   calls in 11 hours

Proportions/Rates/Fractions

2,948 miles in 11 hours  =  ______   miles in 4 hours

68 seats in 4 rows  =  ______   seats in 8 rows

Molar Mass (M)

the mass (m) of one mole of a substance mass is measured in grams (g) molar mass is grams per mole (g/mol) The molar masses of all elements have

been determined and can be found on the Periodic Table of the Elements.

all elements are different molar masses of all elements are different

M is molar mass (in g/mol) m is mass (in grams) n is number of moles Avogadro’s number = 6.022 x 1023

To find the number of atoms/molecules you multiply the # of moles by 6.022 x 1023

If given # of atoms/molecules you divide by avogadro’s number.

Solving mole calculations

1. Find the Molar Mass 2. Rewrite what is given, including the

units You should always have the 3 units, moles,

grams, and g/mole. If you have atoms/molecules you need to first

convert to moles by dividing by avogadro’s number.

2. Setup equal proportions/fractions Numerators (tops) have the same units Denominators (bottoms) have the same units

Solve for the unknown.

What is the mass of 4.7 X 10-2 mol of LiBr.

Determine the number of moles of substance 8.44 g of O2

What is the mass of 3.45 X 1025 atoms of Zn

How many atoms, molecules, or ions would be contained in 150 g of MgSO4

Molar mass The mass of one mole is called “molar mass” E.g. 1 mol Li = 6.94 g Li This is expressed as 6.94 g/mol What are the following molar masses?

S SO2

Cu3(BO3)2

32.06 g/mol 64.06 g/mol

308.27 g/molCalculate molar masses (to 2 decimal places) CaCl2 (NH4)2CO3

O2

Pb3(PO4)2

C6H12O6

110.98 g/mol (Ca x 1, Cl x 2)96.11 g/mol (N x 2, H x 8, C x 1, O x 3)32.00 g/mol (O x 2)

811.54 g/mol (Pb x 3, P x 2, O x 8)180.18 g/mol (C x 6, H x 12, O x 6)

Converting between grams and moles If we are given the # of grams of a compound we

can determine the # of moles, & vise-versa In order to convert from one to the other you must

first calculate molar massg = mol x g/molmol = g g/mol

This can be represented in an “equation triangle”

g

mol

g/mol

g= g/mol x mol0.25HCl

53.15H2SO4

3.55NaCl1.27Cu

Equationmol (n)gg/molFormula

9.136.46

mol= g g/mol0.541998.08

g= g/mol x mol20758.44mol= g g/mol0.020063.55