CHAPTER 7 REVIEW
7.1 THE MOLE
AVOGADRO’S NUMBER……..6.022 X 1023
The atomic mass expressed in grams is the molar mass of an element. It is different for each
element.
To determine the molar mass, we change the units of the atomic mass from atomic mass unit
to grams.
One mole of any element contains 6.022 X 1023 atoms.
1 mole of atoms=____________________atoms
1mole of molecules=_________________molecules
1 mole of ions =_____________________ions
Practice 7.2
What is the mass of 2.50 mole of helium (He)?
Given: 2.50 mole of helium
Find: mass
Plan: molesgrams
(2.50 mol He)(
)= 10.0 grams He
Make sure to write all units and report answers with the correct number of significant figures!
7.2 MOLAR MASS OF COMPOUNDS
To find the molar mass of a compound add all the molar masses of all the atoms in the
compound.
What Is the molar mass for water H2O?
1.Look up the molar masses of each element in the compound
H(1.008g) and O(16.00).
2. Add the masses of all the atoms in the compound.
H2O contains 2 H atoms and 1 O atom
2H= 2(1.008g) = 2.016g
1O= 1(16.00g) =16.00g
= 18.02g= molar mass of H2O
Practice 7.5
What is the mass of 0.150 mol of Na2SO4?
Given: 0.150 mol of sodium sulfate
Find: mass (g)
Plan: 1.Find the molar mass of sodium sulfate and use to 2. Convert molg
1. 2Na = 2(22.99) = 45.98
1S=
1(32.07) = 32.07
4O= 4(16.00) = 64.00
(45.98 + 32.07 + 64.00) = 142.05g molar mass of Na2SO4
2. (0.150 mol Na2SO4) (
Na2SO4) = 21.3g Na2SO4
7.3 PERCENT COMPOSITION OF COMPOUNDS
The percent composition of a compound is ________________________________________.
To find the Percent composition:
Step 1: Calculate the ______________________________.
Step 2: Divide the ________________ of each element in the compound by the molar mass and
multiply by _________.
X 100 = % of the element
Calculate the % composition of sodium chloride
Given: NaCl
Find: % composition
Plan: 1. Calculate the molar mass of NaCl
2.
X 100 = % of the element
1. 1 Na= 1(22.99 g) = 22.99 g
1 Cl = 1(35.45g) = 35.45g
= 58.44 g molar mass of NaCl
2. Na:
Cl:
(100) = 39.34% Na
(100) = 60.66% Cl