1. Stoichiometry and The Mole
Chapter 10
Stoichiometry and The Mole
6.02 X 1023

2. Stoichiometry: What is it?
The word stoichiometry derives from two Greek words: stoicheion (meaning "element") and metron (meaning "measure").
Stoichiometry deals with calculations about the masses (sometimes volumes) of reactants and products involved in a chemical reaction.
It is a very mathematical part of chemistry, so be prepared for lots of calculator use.

3. Measuring Matter
What do the terms ream, gross, dozen, pair have in common?
They are all counting units, designed to make counting objects easier.
Today, we will look at a counting unit for chemistry.

4. Counting Particles What is a Mole????
Chemists need a convenient method for counting
atoms, molecules, and formula units in a sample of substance.
This counting unit is called the Mole.
What is a Mole????
It’s Just like a Dozen only bigger.

5. A mole is… SI base unit used to measure the amount of substance.
It is the number of carbon atoms in exactly 12 grams of Carbon-12.
Has a value of 6.02 x 1023
Called Avogadro’s Number
Named after Amedeo Avogadro
Commonly abbreviated mol.
Just like a dozen only bigger

6. How Big is a Mole ?
6.02 X 1023
Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles.
If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.
If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.
6.02 X 1023
6.02 X 1023
6.02 X 1023
6.02 X 1023

7. Launch Lab To appreciate the magnitude of the mole
To practice dimensional analysis

8. Representative Particles
6.02 X 1023
Molecules for covalently bonded substances
Ex. A water molecule
Formula Units for Ionic Substances
Ex. A formula unit of sodium chloride
Atoms for elements
Ex. An atom of sulfur

9. Converting Moles and Particles
1 mole = 6.02 x particles
Used to convert
Moles to Particles
Particles to Moles

10. Particles to Moles
How many moles of methanol, CH3OH, are there in 6.53 x 1023 molecules of methanol?

11. Avogadro’s Number as Conversion Factor
6.02 x 1023 particles
1 mole or
1 mole
Note that a particle could be an atom OR a molecule!

12. Moles to Particles
A sample containing 0.75 moles of CO2 would contain how many molecules?

13. Examples
How many Fe atoms would be present in 1.27 moles of Fe?

14. Example
4.47 x 1023 molecules of C6H12O6 would be how many moles?

15. Example
Calculate the number of moles contained in 4.50 x atoms of zinc.

16. Example
How many molecules in 2.8 moles of water?

17. Oranges vs Grapes Draw a bowl with one dozen grapes in it.
Draw a bowl with a dozen oranges in it.
Compare the masses.
Why are they not the same?

18. Copper Vs Aluminum Draw a circle. Label it as 1 mole of copper atoms.
Draw another circle.
Label as 1 mole of aluminum atoms.
How many atoms is one mole? Label.
Which weighs more?
Look up masses on periodic table.

19. Molar Mass The mass of one mole of a substance is called "molar mass"
Units g/mol (grams per mole).
Molar mass is the weight in grams of one mole
One mole contains 6.02 x 1023 entities
Therefore, a molar mass is the mass in grams of x 1023 entities

20. Molar Masses
Aluminum
Zinc
Copper
Iron

21. Just as a dozen oranges would not weigh the same as a dozen grapes…
A mole of copper atoms does not have the same mass as a mole of aluminum atoms.
We know that the relative scale for atomic mass uses the carbon-12 isotope as a standard.

22. Each atom of carbon-12 has a mass of 12 amu.
The atomic mass on the periodic table are weighted averages of all isotopes.
Since one mole is defined as the number of carbon-12 atoms in exactly 12 grams of C-12. Therefore…

23. The mass of One Mole of C-12 is 12.0 grams.
Called Molar Mass: the mass in grams of one mole of a pure substance
Example:
An atom of Manganese
Atomic Mass = amu
Molar Mass = g/mol

24. 1 mole Ag= 6.02 x 1023 atoms Ag = 107.87 grams Ag
1 mole K = 6.02 x 1023 atoms K = grams K
1 mole H2 gas = 6.02 x 1023 molecules H2 = 2.02 g H2

25. Mole to Mass Conversions
Calculate the mass in grams of moles of chromium.

26. Mass to Mole Conversions
How many moles of calcium are contained in 525 grams of calcium?

27. Molar Mass of Compounds
Similar mole-mass, mass-mole conversions can be made for compounds
We must know the Molar Mass for the Compound.
How do we calculate Molar Mass of a Compound?

28. Chemical Formulas and the Mole
Recall that for CCl2F2
The subscripts tell us that one molecule of freon contains…
One atom carbon
Two atoms chlorine
2 atoms fluorine

29. Suppose you have one mole of freon molecules there would then be
One mole of carbon atoms
Two moles chlorine atoms
Two moles fluorine atoms

30. What if you have 6 moles of freon?
6 moles of CCl2F2 contains
6 moles carbon atoms
12 moles chlorine atoms
12 moles fluorine atoms

31. Molar Mass of Molecules and Compounds
Mass in grams of 1 mole equal numerically to the sum of the atomic masses
1 mole of CaCl2
1 mole Ca x 40.1 g/mol
+ 2 moles Cl x 35.5 g/mol = g/mol
= g/mol CaCl2

32. The Molar Mass Example
Calculate the molar mass of K2CrO4

33. Example
Calculate the Molar Mass of K2O

34. Learning Check
Prozac, C17H18F3NO, is a widely used antidepressant that inhibits the uptake of serotonin by the brain. Find its molar mass.

35. Converting Mass to Moles
How many moles are represented by 16.0 g of ethanol, C2H5OH ?

36. Converting Mass to Moles
How many moles of NaCl are in 16.0 grams of NaCl?

37. Mass to Moles
How many moles of potassium hydroxide, KOH are in 40.6 g?

38. Mass to Moles
How many moles of glucose, C6H12O6 are in 27.2 g of glucose?

39. Moles to Mass
How many grams in moles of KMnO4?

40. Moles to Mass
How many grams in 1.2 moles of H2O?

41. Moles to Mass
How many grams in 0.87 moles of H2O2?

42. Moles to Mass
How many grams in 0.43 moles of C6H12O6?

43. Calculations with Molar Mass
X molar mass
Grams Moles
Moles Grams
divide by molar mass

44. Learning Check!
The artificial sweetener aspartame (Nutra-Sweet) formula C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame?

45. Atoms/Molecules and Grams
6.02 X 1023 particles = 1 mole AND
1 mole = molar mass (grams)
You can convert atoms/molecules to moles and then moles to grams! (Two step process)
You can’t go directly from atoms to grams!!!! You MUST go thru MOLES.
That’s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first!

46. Molecules to Grams
How many grams of glucose are in 6.63 x 1023 molecules of glucose, C6H12O6?

47. Grams to Molecules
Determine the number of molecules found in a 12.4 g sample of H2SO4.

48. Molecules to grams
3.14 x 1023 molecules of CO2 are produced in a chemical reaction. How much would the sample weigh in grams?

49. Grams to atoms
How many atoms are in a 39.8 g sample of Fe?

50. Mole Road Map
Everything must go through Moles!!!!

51. Converting mass to mole to particles
A sample of AlCl3 has a mass of grams.
How many aluminum ions are present?
How many chloride ions are present?

52. What is the mass in grams of one formula unit of aluminum chloride?

53. Atoms/Molecules and Grams
How many atoms of Cu are present in 35.4 g of Cu?
35.4 g Cu mol Cu X 1023 atoms Cu g Cu mol Cu
= 3.4 X 1023 atoms Cu

54. Learning Check!
How many atoms of K are present in 78.4 g of K?

55. Learning Check!
What is the mass (in grams) of 1.20 X 1024 molecules of glucose (C6H12O6)?

56. Learning Check! How many atoms of O are present in 78.1 g of oxygen?
78.1 g O2 1 mol O X 1023 molecules O2 2 atoms O g O mol O molecule O2

57. Molar Volume Can we apply this mole concept somehow to volume?
At standard temperature and pressure (STP) a mole of any gas will occupy 22.4 liters
Molar STP
1 mole of any = 22.4 Liters
What is STP?
Standard temperature and Pressure
101.3 kpa and 273 K
Arbitrarily chosen conditions that we all agree on so we know the conditions for measuring the volume

58. Convert 427 Liters of CO2 to moles.

59. 37 liters of O2 to moles.

60. How about 3.4 moles of CO to liters?

61. 122 moles of Methane to liters?

62. Mixed Examples
How many molecules are in 22.4 liters of methane?

63. 3.58 x 1023 molecules of propane C8H8 would occupy how much space at STP?

64. You collect 14. 2 liters of CO gas from an experiment
You collect 14.2 liters of CO gas from an experiment. How many molecules would be in the sample?

65. 28 grams of H2 are produce from an experiment
28 grams of H2 are produce from an experiment. How much volume would they displace at STP?

67. Empirical and Molecular Formulas
Many times a chemist is called upon to determine the makeup of chemical compound. This is the job of an analytical chemist… How??? Calculating Percent Composition….

68. Calculating Percent Composition
% by mass = mass of element x 100
mass of compound
Suppose a 100 gram sample of compound is made up of 55 grams of X and 45 grams of Y…
55 g X / 100 g compound x 100 = 55 % X
45 g Y / 100 g compound x 100 = 45 % Y
Percents by mass of all element s in a compound must always add to 100 percent

69. Calculating percent composition from a formula
The percent composition of a formula is always the same.
You can assume the sample size is one mole. This allows the use of molar mass to calculate percent composition.

70. Example: Percent Composition of H2O

71. Percent Composition
What is the percent carbon in C5H8NO4 (the glutamic acid used to make MSG monosodium glutamate), a compound used to flavor foods and tenderize meats?

72. Empirical Formula
Suppose we know the elements in a sample of a new compound…
We can use this data to determine the formula of the compound.
How?

73. Chemical Formulas of Compounds
Formulas give the relative numbers of atoms or moles of each element in a formula unit - always a whole number ratio (the law of definite proportions).
NO atoms of O for every 1 atom of N
1 mole of NO2 : 2 moles of O atoms to every 1 mole of N atoms
If we know or can determine the relative number of moles of each element in a compound, we can determine a formula for the compound.

74. Types of Formulas Empirical Formula
The formula of a compound that expresses the smallest whole number ratio of the atoms present.
Ionic formula are always empirical formula
Molecular Formula
The formula that states the actual number of each kind of atom found in one molecule of the compound.

75. If the two formulas are different the molecular formula is a simple multiple of the empirical formula.
For example:
Hydrogen Peroxide
Empirical Formula is HO.
Molecular Formula is H2O2

76. To obtain an Empirical Formula
1. Determine the mass in grams of each element present, if necessary.
2. Calculate the number of moles of each element.
3. Divide each by the smallest number of moles to obtain the simplest whole number ratio.
If whole numbers are not obtained* in step 3), multiply through by the smallest number that will give all whole numbers
* Be careful! Do not round off numbers prematurely

77. How to find empirical formula
Percent to Mass
Mass to Moles
Divide by small
Multiply ‘til whole

78. A sample of a brown gas, a major air pollutant, is found to contain 2
A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine a formula for this substance.
require mole ratios so convert grams to moles
moles of N = 2.34g of N = moles of N
14.01 g/mole
moles of O = g = moles of O
16.00 g/mole
Formula:

79. Empirical Formula from % Composition
A substance has the following composition by mass: % Na ; % B ; % H
What is the empirical formula of the substance?

80. Molecular Formula
Since two compounds can have the same Empirical Formula we must determine the actual formula.
Called Molecular Formula.

81. Steps to Determine Molecular Formula
Determine the molar mass of the actual compound through an experiment.
Calculate the molar mass of the empirical formula.
Divide the actual mass by the mass of the empirical formula.
The result shows how many times bigger the molecular formula is than the empirical formula. Multiply all subscripts in the empirical formula by this factor.

82. Calculation of the Molecular Formula
A compound has an empirical formula of NO2. The colorless liquid, used in rocket engines has a molar mass of 92.0 g/mole. What is the molecular formula of this substance?

83. Hydrates: A compound that has a specific number of water molecules bound to its atom
Formulas
Examples
Sodium carbonate decahydrate Calcium chloride dihydrate Magnesium sulfate heptahydrate Iron (III)phosphate tetrahydrate

85. Analyzing a hydrate
A hydrate can be analyzed by driving off the water with heat.
The remaining substance is called the Anhydrous salt… meaning “without water”
Some hydrates are a color different than their anhydrous salt…
Cobalt (II) chloride hexahydrate is pink
Without water it is blue.

86. Determining the Formula of a Hydrate
MgSO4* ?H2O
Heat the sample to drive off all water.
Mass the anhydrous compound.
mass of water = Mass of hydrate – mass of anhydrous salt
Convert these masses to moles.
Calculate the mole ratio between the compound and the water molecules.

87. Uses of hydrates
Mainly used as dessicants: substances used to keep things moisture free by absorbing excess water.