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!