THE MOLE

1
THE MOLEn

• The mole term is similar to the dozen term.
• Just as a dozen represents 12 the mole
  represents 6.022 x 1023. A very large amount.
• This is due to atoms molecules being very small.

• The mole is also referred to as Avogadros
  number, NA
• 1 mole NA n 6.022 x 1023 particles
• Particles could be atoms, molecules, ions,
  electrons, even eggs.

2
THE MOLE ATOMIC MASS

• The atomic mass (weight) is measured in reference
  to the mole.
• The atomic mass is also known as the MOLAR MASS.
• The atomic mass mass of an element DIVIDED by 1
  mole of that element.

• Atomic mass mass/mole or m/n.
• Units for atomic mass is grams per mole or g/mol.
• For example
• H 1.008 amu
• 1.008 g/mol
• 6.022 x 1023 atoms
• 1 molar mass

3
CALCULATIONS INVOLING THE MOLE.

• Fill in the blank.
• A mole of oxygen atoms contain _______ atoms and
  weighs ______ grams.
• A mole of oxygen contains _____ molecules and
  ____ atoms and weighs _______ grams.

• A mole of fluorine atoms contain _________ atoms
  and weighs _____grams.
• A mole of fluorine contains __________ molecules
  and ________ atoms and weighs ______ grams.

6.022 x 1023
6.022 x 1023
15.999
19.00
6.022 x 1023
6.022 x 1023
2(6.022 x 1023 )
12.044 x 1023
31.998 or 2(15.999)
38.00
4
CALCULATIONS INVOLING THE MOLE.

• How many atoms of Mg are contained in 15.0 grams
  of Mg?
• Answer
• 15.0 g (1 mole/24.3g)
• 0.617 moles.
• then
• 0.617 mol (6.022 x 1023 atoms/ 1 mole) 3.72 x
  1023 atoms.

• Dimensional Analysis Approach.
• How many moles of Mg are contained in 15.0 grams
  of Mg?
• Answer
• 15.0 g (1 mole/24.3g)
• 0.617 moles.
• Remember if g is on top originally then inside
  the parenthesis it must go on the bottom.

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MOLAR MASS FOR COMPOUNDS

• The molar mass of any substance is the mass in
  grams for one mole of that substance.
• H2SO4 contains 2-H atoms, 1-S atoms 4-O atoms.
  Each of those atoms contribute mass to the whole
  compound.
• 2H 1S 4O H2SO4
• so
• 2(1.008 g/mol) 1(32.06 g/mol) 4(15.99 g/mol)
• 98.04 g/mol

• Calculate the molar mass of the following
  compounds.
• 1. K3PO4
• 2. Ca(OH)2
• 3. (NH4)2SO3
• 4. SrCl2 . 6H2O
• answer on next page.

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MOLAR MASS FOR COMPOUNDS

• Answer to molar mass question.
• 1. 3K P 4O
• 212 g/mol
• 2. Ca 2O 2H
• 74 g/mol
• 3. 2N 8H S 3O
• 116 g/mol
• 4. Sr 2Cl 12H 6O
• 267 g/mol

• Word Problems
• How many grams does one molar mass of BaCO3
  weigh?

Answer 197 g/mol
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CALCULATIONS INVOLING THE MOLE for COMPOUNDS.

• How many atoms are in 6.34 g of (NH4)3PO4
• Answer
• 3N 12H P 4O 149 /mol
• then
• 6.34 g (1 mole/149 g)
• 0.0426 moles.
• then
• 0.0426 mol (6.022 x 1023 formula units/ 1 mole)
  (20 atoms/1 formula unit) 5.12 x 1023 atoms.

• Dimensional Analysis Approach.
• How many grams of NH4NO3 are contained in 3.15
  moles of NH4NO3?
• Answer
• 2N 4H 3O 80 g/mol
• 3.15 mol (80 g/mol)
• 252 g
• Remember if mol is on top originally then
  inside the parenthesis it must go on the bottom.

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Challenge MOLE problems.
What mass of sodium will contain the same number
of atoms as 100.0 g of potassium? 100.0g K (1
mole K / 39.1 g K) (6.022x1023 K-atoms/1 mole K)
1.540 x 10 24 K-atoms. Now
since atoms of K atoms of Na 1.540x1024 atoms
Na (1 mol/ 6.02 x1023 atoms) (22.98 g/ 1 mol)
58.77 g of Na
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Challenge MOLE problems.
A solution of sulfuric acid contained 65 H2SO4
by mass and had a density of 1.56 g/mL. How
many moles of acid are present in 1.00 L of the
solution? 1.00L (1000 mL/1L) 1000 mL of
solution dV m 1000 mL (1.56 g/mL) 1560
g of solution but only 65 of the solution is
H2SO4 therefore 65 (x / 1560 g) 100 so x
mass of H2SO4 1014 g 1014 g H2SO4 (1 mole /
98.04 g) 10.3 moles
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PRACTICE PROBLEM 10

• 1. What is the molar mass of Fe(NO2)3.6H2O
• 2. How many moles are contained in 750.0 g of
  Fe(NO2)3?
• 3. How many grams of iron are contained in 0.097
  mol of Fe2(CO3)3?
• 4. How many atoms are contained in 25.0 g of
  nitrogen (N2)?
• 5. How many grams of potassium nitrite will
  contain 6.78 x 1024 potassium atoms?
• 6. If 25.0 g of calcium chloride reacted with
  25.0 g of sodium carbonate, how many moles of
  each will be reacting?

301.9 g/mol
3.868 mol
11 g
1.07 x 1024 N-atoms
957 g
CaCl2 0.225 mol Na2CO3 0.236 mol
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GROUP STUDY PROBLEM 10

• ______1. What is the molar mass of Ba(NO3)2.4H2O
  
• a) 185.0 b) 261.0 c) 333.3 d) 1044
• ______2. How many moles are contained in 54.78g
  of Cu(NO3)2?
• a) 0.2921mol b) 3.424mol c) 187.5mol d)
  0.399
• ______3. Which contains the larger number of
  molecules?
• a) 125.0 g HCl b) 15.0 g C6H12O6 c)
  170.0 g of I2
• ______4. How many grams of silver are contained
  in 0.754 mol of AgNO3?
• a) 0.488 g b) 81.3 g c) 128g d) 170g
• ______5. 7.0 g of nitrogen (N2) contains
• a) 7.0 atoms of N c) 3.0 x 1023 atoms
  of N
• b) 0.25 mole of N d) 7.0 atomic
  masses of N
• ______6. How many atoms are in 56.9 g of
  potassium nitrite?
• ______7. If 16.054 g of calcium chloride reacted
  with 25.004 g of sodium carbonate, how many moles
  of each will be reacting?