# Using Chemical Formulas - Belle Vernon Area School District

7.3

 Formula Mass – for any molecule, formula unit, or ion, it is the ____ of the ________ masses of all atoms represented in its formula.

H

2

O for example is

H = 1.008 x 2 = 2.016 amu

 O = 15.999 x 1 = 15.999 amu

 Total = 18.015 amu

 Try to find the mass of

KClO

3

Ca(NO

3

)

2

 MgCl

2

H

2

SO

4

PO

4

3-

 The mass of 1 mol of a substance in g/mol

 H

2

O for example is

 H = 1.008 x 2 = 2.016 g/mol

 O = 15.999 x 1 = 15.999 g/mol

 Total = 18.015 g/mol

 The ___ mass is numerically = to the ___ mass

 You can convert grams to moles and vice versa using ______ ______

 You can also convert atoms to moles and vice versa using ___________ #

 What is the mass in grams of 2.50 mol of oxygen gas?

 How many moles are in 100 g of H

2

O?

 How many moles are in 10 grams of

Carbon?

 How many moles are in 3.01 x 10 23 molecules of CH

4

?

 How many atoms are in 15 moles of S?

 How many molecules are there in the following…

 25.0 g H

2

SO

4

 125 g Sugar C

6

H

12

O

6

 How many grams are in…

 6.5 x 10 23 atoms of Cu

 5.12 x 10 30 molecules of CH

4

Percent Composition – the % by mass of each _________ in a cmpd

 To calculate % Comp, determine

_______ mass of entire compound.

 Calculate the % of each element by

__________ the mass of each

___________ by the molar mass.

 Determine the percent composition of Al and O in

Al

2

O

3

.

 Determine the composition of

Al, S, and O in Al

2

(SO

4

)

3

 Find the % comp of each element in the following

PbCl

2

Ba(NO

3

)

2

Find the % water in ZnSO4•7H

2

O

 Mg(OH)

2 is 54.87% O by mass. How many g of O are in 175 g of the cmpd?

How many moles of O is this?

 Complete the section review on page 244 numbers 1-6. This is due at the beginning of class tomorrow!