Download Moles, Atoms, Molecules 10C

Chem I Ch 10 Notes/ Chem I H chapter 11 notes
10A
The atomic mass is found by checking the periodic table.
The atomic mass is the number of grams of an element that is
numerically equal to the mass of an atomic mass unit.
atomic mass C = 12.0 g
The atomic mass is the mass of one mole of atoms.
Mole – quantity such that there are as many atoms as in
12 g of carbon
The mass of a mole of NaCl is the molar mass.
1 atom
1 mole
1 molecule
C
12.0 u
12.0 g
Cl2
Fe
55.8 u
55.8 g
H 2O
Cu
63.5 u
63.5 g
2Cl
2H
1 mole
2 X 35.5u = 71.0u
71.0 g
2 X 1.0u = 2.0u
1O 1 X 16.0u = 16.0u
18.0 g
18.0u
C3H6 3C 3 X 12.0u=36.0u
6H
6 X 1.0u= 6.0u
42.0u
1 formula unit
Al2(SO4)3
2Al,
2 X 27.0u = 54.0u
3S,
3 X 32.1u = 96.3u
12 O,
12 X 16.0u = 192.0u
342.3u
1 mole
342.3 g
42.0 g
Notes Converting grams to moles
10B
To convert first write what you are given.
Then “times sign draw a line”.
Place what you want above the line and the given below the line.
“mol” always has a coefficient of 1.
Where you see “g”, go to the periodic table to find the value.
Ex 1 How many grams are in 6.50 moles of H2SO4?
6.50 moles ×
98.1 g
= 638 g
1 mol
2H
2 X 1.0 = 2.0g
1S
1 X 32.1 = 32.1g
4O
4 X 16.0 = 64.0g
98.1g
Ex 2 What is the mass in grams of 5.90 mol C8H18? 8C 8 X 12.0 = 96.0g
5.90 mol 
114.0 g
 673g
1mol
18H 18 X 1.0 = 18.0g
114.0g
Ex 3 What is the number of moles in 432 g Ba(NO3)2?
1 Ba 1 X 137.3 = 137.3g
2 N
2 X 14.0 = 28.0g
6O
6 X 16.0 = 96.0g
261.3g
432 g 
1 mol
 1.65 mol
261.3 g
Moles, Atoms, Molecules
10C
Representative particle - atom, molecule, or formula unit.
A mole of a substance contains
6.02 X 1023 representative particles
Avogadro’s number = 6.02 X 1023
Mole – SI unit used to measure number of representative
particles in a substance
A dozen is to eggs as mole is to atoms.
Conversion questions to answer – What’s the unknown
What is given
How many times signs
Molecules will always have 1 or 6.02 X 1023
EX 1
How many moles of magnesium is 1.25 X 1023 atoms of
magnesium?
1.25 × 10 23 atoms ×
1 mol
6.02 × 10 23 atoms
= 0.208 mol
EX 2
How many atoms are in 2.12 mol of C3H8 (propane)?
6.02  1023 molecules 11 atoms
2.12 mol 

 1.40  1025 atoms
1 mol
molecule
Percent Composition
% mass 
mass of element
 100%
mass of compound
Ex 1
Find the % composition of C3H8.
3C 3 X 12.0 = 36.0g
8H 8 X 1.0 = 8.0g
44.0g
%C 
36.0g
 100%  81.8%
44.0g
%H 
8.0g
 100%  18.2%
44.0g
Ex 2
What is the percentage of nitrogen in NH3?
1N 1 X 14.0 = 14.0g
3H 3 X 1.0 = 3.0g
17.0g
%N 
14.0g
 100%  82.4%
17.0g
10D
Empirical Formulas
10E
Empirical formula – lowest whole-number ratio of the elements
in a compound (divide by – Greatest Common Factor)
CNH4 not C2N2H8
Empirical Formula Calculations
1. Change the given information to moles for each
element.
2. Divide each mole answer by the smallest
number of moles.
3. If the answers from step 2 are not whole numbers
then divide by the smallest decimal part.
4. Write the formula with the mole ratio as subscripts.
EX 1 Find the empirical formula. A compound contains
9.31g of Ag and 0.69g of O.
9.31g Ag 
1 mol
0.0866

2
107.9g
0.0431
0.69g O 
1 mol
0.0431

1
16.0g
0.0431
Ag2O
EX 2 A compound contains 25.9% N and 74.1% O.
Find the empirical formula.
25.9g N 
1 mol
1.85

1
14.0g 1.85
74.1g O 
1 mol
4.63

 2.50
16.0g
1.85
N2O5
1.5 = 2
2.50  .5 = 5
Molecular Formulas
10F
Molecular formula – empirical formula or its multiple
Several compounds can have the same empirical formula but
different molecular formulas.
Convert
molecular  empirical
Divide subscripts by greatest common factor
empirical  molecular
multiply subscripts by
molar mass
empirical formula mass
EX 1
The empirical formula is CH4N and the molar mass is 60.0 g.
Find the molecular formula.
C
1 X 12.0 = 12.0g
4H 4 X
1.0 =
4.0g
60.0g
2
30.0g
C2H8N2
N 1 X 14.0 = 14.0g
30.0g
EX 2
Find the molecular formula of C4H6O if the molar mass is
280.0g.
4C
1 X 12.0 = 48.0g
6H 4 X
1.0 =
6.0g
O 1 X 14.0 = 16.0g
70.0g
280.0g
4
70.0g
C16H24O4
Name______________________Pd._____ Date_________
Chem I H Chapter 11 Notes/ Chem I Chapter 10 Notes
10A
The atomic mass is found by checking the __________ ______.
The _____________ ________ is the number of grams of an
element that is numerically equal to the mass of an atomic
mass unit.
(atomic mass C = 12.0 g)
The atomic mass is the mass of one ____________ of atoms.
Mole – quantity such that there are as many atoms as in 12 g of
carbon
The mass of a mole of NaCl is the ______________ ________.
1 atom
1 mole
1 molecule
C
12.0 u
12.0 _
Cl2
2Cl
2 X 35.5u =
Fe
55.8 u
55.8 _
H 2O
2H
2 X 1.0u =
Cu
63.5 u
63.5 _
1O
1 X 16.0u =
C3H6
3C
3X
6H
6x
1 formula unit
Al________________________
Al2(SO4)3
S________________________
O ________________________
1 mole
1 mole
71.0 _
Ch 10 Notes Converting grams to moles
10B
To convert first write what you are ______________________.
Then “times sign__________________________________”.
Place what you want above the line and the given below the line.
“mol” always has a coefficient of __________.
Where you see “g”, _______ to the periodic table to find the value.
Ex 1 How many grams are in 6.50 moles of H2SO4? Show all work
2H
________________________
____________________
1S
____________________
4O
____________________
____________________
Ex 2 What is the mass in grams of 5.90 mol C8H18? 8C__________
____________
______________________________
Ex 3 What is the number of moles in 432 g Ba(NO3)2?
Ba
N
O
_____________________________________
g
Moles, Atoms, Molecules
10C
Representative particle - atom, molecule, or _________ _____
A mole of a substance contains
____________________
representative particles
Avogadro’s number = ______________________
_________– SI unit used to measure number of representative
particles in a substance
A dozen is to eggs as mole is to atoms.
Conversion questions to answer – What’s the ______________
What is given
How many times _________
Molecules will always have 1 or ___________________
EX 1
How many moles of magnesium is 1.25 X 1023 atoms of
magnesium?
___________________________________________
EX 2
How many atoms are in 2.12 mol of C3H8 (propane)?
___________________________________________
Percent Composition
% mass 
mass of element
 100%
mass of compound
Ex 1
Find the % composition of C3H8.
3C ______________
8H ______________
_____
_____________________________
_____________________________
Ex 2
What is the percentage of nitrogen in NH3?
1N ______________
3H ______________
_____
_____________________________
10D
Empirical Formulas
10E
Empirical formula – lowest __________________
ratio of the elements in a compound
(divide by – Greatest Common Factor)
i.e.
CNH4 not C2N2H8
Empirical Formula Calculations
5. Change the given information to __________ for each
element.
6. Divide each mole answer by the _________________
number of moles.
7. If the answers from step 2 are not whole numbers
then divide by the smallest decimal part.
8. Write the formula with the mole ratio as ___________.
EX 1 Find the empirical formula. A compound contains
9.31g of Ag and 0.69g of O.
9.31 g Ag X
0.69 g O
X
Which answer is the smallest number?____________________
9.31g Ag 
1 mol
0.0866

2
107.9 g
0.0431
0.69 g O 
1 mol
0.0431

1
16.0 g
0.0431
______________________
EX 2 A compound contains 25.9% N and 74.1% O.
Find the empirical formula. (Hint: change % to grams)
Molecular Formulas
10F
Molecular formula – empirical formula or its ______________
Several compounds can have the same _____________ _____
but different molecular formulas.
Convert
molecular  empirical
Divide subscripts by ______________ __________ _________
empirical  molecular
multiply subscripts by ___________________
EX 1
The empirical formula is CH4N and the molar mass is 60.0 g.
Find the molecular formula.
C 1 X 12.0 = 12.0g
4H 4 X 1.0 = 4.0g
N 1 X 14.0 = 14.0g
30.0g
__________________
EX 2
Find the molecular formula of C4H6O if the molar mass is
280.0g.
4C 1 X 12.0 = 48.0g
6H 4 X 1.0 = 6.0g
O 1 X 14.0 = 16.0g
70.0g
____________________
Ch 10 Test Reference
Percent Composition
% mass 
mass of element
 100%
mass of compound
Empirical Formula Calculations
1. Change the given information to moles for each
element.
2. Divide each mole answer by the smallest
number of moles.
3. If the answers from step 2 are not whole numbers
then divide by the smallest decimal part.
4. Write the formula with the mole ratio as subscripts.
Convert
molecular  empirical
Divide subscripts by greatest common factor
Convert
multiply subscripts by
empirical  molecular
molar mass
empirical formula mass