1. The Mole & Stoichiometry
Quantitative study of substances and their relationship to each other in chemical reactions.
The “Math” of Chemistry

2. The Mole Similar to how a dozen = 12 things
One mole = 602 billion trillion things 602,000,000,000,000,000,000,000
6.02 X 1023 (in scientific notation)

3. 6.02 X 1023 is called Avogadro’s number.
Amedeo Avogadro
(1776 – 1856)
Mole is abbreviated mol
(gee, that’s a lot quicker to write, huh?)

4. Just How Big is a Mole?
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.

5. Mole Concept A mole is equal to 3 things:
1 mole = gram formula mass (molar mass)
1 mole = 6.02 X 1023 particles
1mole = 22.4 liters of a gas at STP

6. Mole Conversions

7. The Mole 1 mole Al = 6.02 X 1023 “atoms”
1 mole H2O = 6.02 x 1023 “molecules”
Note:
the NUMBER of particles is always the same, but the MASS of each mole will be very different!
This is because atoms have different atomic masses.

8. Molar Mass Molar Mass = Mass of 1 mole of particles (in grams)
Use average atomic mass rounded to the nearest whole number
1 mole of C atoms = 12 g
1 mole of Mg atoms = 24g
1 mole of Cu atoms = 63.5 g

9. Learning Check! Find the molar mass = ________ g/mole
1 mole of Br atoms
1 mole of Sn atoms
= ________ g/mole

10. Molar Mass of Molecules and Compounds
Called “gram formula mass” or “molecular mass”
Add up atomic masses of atoms in the formula
1 mole of CaCl2
1 mole Ca x 40 g/mol
+ 2 moles Cl x 35.5 g/mol = 111 g/mol

11. Learning Check! Molar Mass of K2O = ________
B. Molar Mass of Al(OH)3 = ________

12. Learning Check
Prozac, C17H18F3NO, is a widely used antidepressant that inhibits uptake of serotonin by the brain. Find molar mass.
C: 12 g/mol x 17 =
H: 1 g/mol x 18 =
F: 19 g/mol x 3 =
N: 14 g/mol x 1 =
O: 16 g/mol x 1 = Total = g/mol

13. Calculations with Molar Mass
# moles = given mass (grams)
gram-formula mass

14. Converting Moles and Grams
Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?
3.00 moles Al ? g Al

15. On Ref Tables find molar mass of Al
1 mole Al = 27 g Al
3.00 moles Al = x grams
27 g/mol
Answer = 81 g Al

16. Mole/Gram Conversion Practice
If you have 30 grams of CO2 how many moles do you have?
If you have 6 moles of MgBr2 how many grams do you have?

17. 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?

18. Add up the formula mass
C: 12 g/mol x 14 =
H: 1 g/mol x 18 =
N: 14 g/mol x 2 =
O: 16 g/mol x 5 = Total = g/mol
# moles = ____grams = ______ mol
g/mol

19. Particles and Moles 1 mole = 6.02 x 1023 particles
# Moles = # particles
6.02 x 1023 particles

20. A Mole of Particles Contains 6.02 x 1023 particles
= x 1023 C atoms
= x 1023 H2O molecules
= x 1023 NaCl “formula units”
(technically, ionics are compounds not molecules so they are called formula units)
1 mole C
1 mole H2O
1 mole NaCl

21. A Mole of Gas 1 mole = 22.4 Liters of any gas at STP
# Moles = # liters of gas (at STP)
22.4 Liters

22. Percent Composition and
Chemical Quantities
Percent Composition and
Empirical Formulas
Copyright © by Pearson Education, Inc.
Publishing as Benjamin Cummings

23. Percent Composition Formula on Ref. Tables
% Comp. by Mass = Mass of Part x 100
Mass of Whole

24. Percent Composition
Is the percent by mass of each element in a formula.
Ex: Calculate the percent composition of CO2.
CO2 = 1 (12g) + 2 (16 g) = 44 g/mol)
12. g C x = % C
44g CO2
32 g O x = % O
44 g CO2

25. Learning Check What is the percent composition of lactic acid,
C3H6O3, a compound that appears in the blood
after vigorous activity?

26. Solution STEP 1 3 (12) + 6 (1) + 3 (16) = 90 g/mol STEP 2
%C = 36 g C x 100 = 40% C
90 g
%H = 6 g H x 100 = 6.7% H
%O = 48 g O x 100 = 53.3% O

27. 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?
a) %C
b) %C
c) %C

28. Solution 64.58 %C Molar mass C7H14O2 =
7(12) + 14(1) + 2(16) = 130g/mol
% C = 84g C x 100 = 64.6 % C
130g

29. You Try
The chemical isoamyl acetate C7H14O2 gives the odor of pears. What is the percent carbon in isoamyl acetate?
1) %C
2) %C
3) %C

30. Percent of Water in a Hydrate
Hydrate: an ionic compound with water molecules loosely attached.
Ex: BaCl2 ∙ 2H2O
Anhydrous Salt: the hydrate with the water driven off by heating in a crucible

32. Finding % from Formula
Ex: BaCl2 ∙ 2H2O

33. Finding % from Experimental Data
Ex: If 11 grams of an unknown hydrate is heated in a crucible to a constant mass of 9.5 grams calculate the % of water that was in the hydrate.

34. Chemical Formulas and Moles
Formulas can tell us:
Relative number of atoms of each element in compound
Ex: NO atoms of O for every 1 atom of N
Mole ratio of each element in a formula unit
Ex: 1 mole of NO2 contains 2 moles of O atoms to every 1 mole of N atoms
Thus 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.

35. Types of Formulas
Empirical Formula: expresses smallest whole number ratio of the atoms present.
Ex: ______________
(Note: Ionic formulas are always empirical)
Molecular Formula: states actual number of each kind of atom found in one molecule of the compound.

36. Writing Empirical Formulas
The simplest whole number ratio of the atoms.
Some molecular formulas can be reduced to their empirical form
Calculated by dividing the subscripts in the actual (molecular) formula by a whole number to give the lowest ratio.
C5H10O5  = C1H2O1 = CH2O
actual (molecular) empirical
formula formula

37. Molecular and Empirical Formulas
The molecular formula is the same or a multiple of the empirical.

38. Learning Check A. What is the empirical formula for C4H8?
1) C2H4 2) CH2 3) CH
B. What is the empirical formula for C8H14?
1) C4H7 2) C6H12 3) C8H14
C. Which is a possible molecular formula for CH2O?
1) C4H4O4 2) C2H4O ) C3H6O3

39. Find Empirical Formula Given Grams
1. Determine the mass in grams of each element present, if necessary.
2. Calculate number of moles of each element.
Divide each by the smallest number of moles to obtain the simplest whole number ratio.
Note:
If whole numbers are not obtained* multiply through by the smallest number that will give all whole numbers

40. Find Empirical Formula Given Grams
A compound contains 7.31 g Ni and 20.0 g Br. Calculate its empirical (simplest) formula.

41. Solution Convert 7.31 g Ni and 20.0 g Br to moles.
Moles of Ni = 7.31 g Ni = mol Ni
59 g Ni
Moles of Br = 20.0 g Br = mol Br
80 g Br
Divide by smallest # moles to get ratio
0.124 mol Ni = 1 Ni mol Br = 2 Br
Write ratio as subscripts: NiBr2

42. Converting Decimals to Whole Numbers
When number of moles for an element is a decimal, all the
moles are multiplied by a small integer to obtain whole number.

43. 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 empirical formula:
You need mole ratios so convert grams to moles
moles of N = 2.34g of N = _______moles of N
14 g/mole
moles of O = g = _________moles of O
16 g/mole
Formula: _______________

44. Empirical Formula from % Composition
A substance has the following composition by mass:
60.80 % Na ; % B ; % H
What is the empirical formula of the substance?

45. Consider a sample size of 100 grams
60.80 grams of Na
28.60 grams of B
10.60 grams H
Determine the number of moles of each
Determine the simplest whole number ratio

46. Empirical Formula from % Composition
Aspirin is 60.0% C, 4.5 % H and 35.5 % O. Calculate its empirical (simplest) formula.

47. Solution Calculate moles of each element in 100 g.
100 g aspirin contains 60.0% C or 60.0 g C, 4.5% H or 4.5 g H, and 35.5% O or 35.5 g O.
60.0 g C = mol C
12 g C
4.5 g H = mol H
1 g H
35.5 g O = mol O
16 g O

48. Solution (continued) Divide by the smallest number of mol.
5.00 mol C = mol C (decimal)
2.22
4.5 mol H = 2.0 mol H
2.22 mol O = mole O

49. Solution (continued) Use the lowest whole number ratio as subscripts
When the moles are not whole numbers, multiply by a factor to give whole numbers, in this case x 4 .
C: mol C x 4 = 9 mol C
H: 2.0 mol H x 4 = 8 mol H
O: mol O x 4 = 4 mol O
Using these whole numbers as subscripts the simplest formula is
C9H8O4

50. Finding the Molecular Formula
Molecular Mass (GFM) of a compound is either equal to or some whole number multiple of the empirical formula’s mass.
Molecular Mass = “Magic Number”
Empirical Mass
Distribute this number through the Empirical formula to determine the Molecular formula

51. Finding 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?

52. Finding the Molecular Formula
A compound has an empirical formula of CH2O. The white crystal, has a molar mass of g/mole. What is the molecular formula of this substance?