1. The Mole
Chapter 11

2. Measuring Matter Section 11.1
Chemists need a convenient method for counting the number of atoms, molecules or formula units in a sample of a substance.
Atoms and molecules are so small that chemists created their own counting unit called the mole

3. What is a mole?
Mole- abbreviated mol is the SI base unit used to measure the amount of a substance
A mole of anything contains 6.02 x1023 representative particles
This number is known as Avogadro’s number

5. Conversion Factors Example: 4800g to kg Conversion factor: 1000g= 1kg
Recall from chapter 2:
A method of problem solving that focuses on the units to describe matter
Conversion factor- a ratio of equivalent values used to express the same quantity in different units
Example: 4800g to kg
Conversion factor: 1000g= 1kg

6. One mole = 6.02 x1023 representative particles
Conversion factor:
# particles = # of moles x

7. Practice Determine the number of atoms in 2.50 mol of Zn.
Calculate the number of molecules in 11.5 mol H2O.

8. How many moles contain each of the following:
5.75 x1024 atoms Al
3.58 x1023 formula units of ZnCl2

9. Mass and the Mole Section 11.2
Molar Mass- The mass in grams of one mole of any pure substance
Units: grams/mol
Example: Manganese has an atomic mass of amu there fore it has a molar mass of g/mol

10. Suppose you are in a chemistry lab and you need 3
Suppose you are in a chemistry lab and you need 3.00 moles of manganese. What amount would you weigh out on the scale?
What information do I need to know?
What information is given in the problem?

11. Determine the mass in grams:
3.57 mol Al
2.45 mol Zn
42.6 mol Si

12. Convert using molar mass
Atoms or Molecules
MOLES
Grams
Convert using
6.02 x1023
Convert using molar mass

13. How many atoms are in each of the following samples?
55.2 g Li
0.120 kg Ti

14. Moles to Compounds Section 11.3
Recall that the chemical formula of a compound indicates the types of atoms and the number of each contained in one formula unit of the compound
Example: CCl2F2 (Freon)
1 carbon
2 chlorine
2 fluorine

15. Determine the number of moles of chloride ions in 2.50 mol ZnCl2
What information is given in the problem?
2.50 mol ZnCl2
2 mol Cl- ions : 1 mol ZnCl2

16. Practice Problem
How many moles of oxygen atoms are present in 5.00 mol diphosphorus pentoxide?

17. The Molar Mass of Compounds
Molar mass of a compound is determined by adding the masses of all elements present.
# of moles x molar mass = number of grams
Example: K2CrO4
2 mol K x g K = g
1 mol K
1 mol Cr x g Cr = g
1 mol Cr
4 mol O x g O = g
1 mol O
78.20 g
52.00 g g
g K2CrO4

18. Practice Problems
Determine the molar mass of each of the following compounds:
NaOH
Sr(NO3)2
(NH4)PO4
C12H22O11
C2H5OH

19. Answers  Determine the molar mass of each of the following compounds:
NaOH g/mol NaOH
Sr(NO3)2  g/mol Sr(NO3)2
(NH4)PO4  g/mol (NH4)PO4
C12H22O11 g/mol C12H22O11
C2H5OH  g/mol C2H5OH

20. Mole- to- Mass Conversion
Atoms or Molecules
MOLES
Grams
Convert using
6.02 x1023
Convert using molar mass

21. Convert using molar mass
Example
What is the mass of 3.25 moles of sulfuric acid (H2SO4)?
What am I given in the problem?
What do I need to know?
3.25 mol H2SO4
Atoms or Molecules
MOLES
Grams
Convert using
6.02 x1023
Convert using molar mass

22. 3.25 mol H2SO4
Determine the number of moles present in 22.6 g AgNO3

23. Converting the mass of a compound to number of particles
Atoms or Molecules
MOLES
Grams
Convert using
6.02 x1023
Convert using molar mass

24. Practice Problem
A sample of silver chromate (AgCrO4) has a mass of 25.8g.
How many Ag+ ions are present?
How many CrO4 2- ions are present?
What is the mass in grams of one formula unit of silver chromate?

25. How many Ag+ ions are present?
How many CrO4 2- ions are present?
What is the mass in grams of one formula unit of silver chromate?

26. Empirical and Molecular Formulas Section 11.4
The percent by mass of each element in a compound is called the percent composition of a compound
mass of element x 100 = percent by
mass of compound mass

27. Practice Problem
Calculate the percent composition of baking soda (NaHCO3) (Molar Mass= 84 g/mol) Na H C O

28. Which has the larger percent of sulfur, H2SO3 or H2S2O8?

29. Empirical Formula
Empirical Formula- formula with the smallest whole number mole ratio of the elements
Starting with the percent composition- drop the percentage sign and replace it with grams
Multiply the mass of each element by the conversion factor that relates moles to grams (molar mass)
Calculate the simplest whole number ratio of moles of the elements by dividing each number of moles by the smallest value in the mole ratio.
If a fraction is present- multiply by 2 to produce a whole number

30. Practice Problem
Determine the empirical formula for a compound that contains 35.98% aluminum and 64.02% sulfur.

31. Molecular Formula
Molecular Formula- specifies the actual number of atoms of each element in one molecule or formula unit of the substance
experimentally determined molar mass = n
mass of empirical formula
Molecular formula = (empirical formula) n

32. Practice Problem
A colorless liquid composed of 46.68% nitrogen and 53.32% oxygen has a molar mass of g/mol. What is the molecular formula?

33. The Formula of a Hydrate Section 11.5
A hydrate is a compound that has a specific number of water molecules bound to its atoms.
The number of water molecules bound to its atoms is indicated with a prefix
Prefixes in Hydrates
Number of Atoms
Prefix 1
Mono- 6
Hexa- 2
Di- 7
Hepta- 3
Tri- 8
Octa- 4
Tetra- 9
Nona- 5
Penta- 10
Deca-

34. Determining the formula of a hydrate
A mass of 2.50 g of blue, hydrated copper sulfate (CuSO4 ·x H2O) is placed in a crucible and heated. After heating, 1.59g white anhydrous copper sulfate (CuSO4) remains.
What is the formula for the hydrate? Name the hydrate.

35. Known: Unknown: Determine the mass of water lost.
Mass of hydrated compound: 2.50 g CuSO4 ·x H2O
Mass of anhydrous compound: 1.59 g CuSO4
Molar mass of CuSO4: g/mol CuSO4
Molar mass of H2O: g/mol H2O
Unknown:
Formula of hydrate:
Name of hydrate:
Determine the mass of water lost.
Calculate the number of moles of H2O and anhydrous CuSO4 using the molar mass.
Determine the value of x= moles H2O ÷ moles CuSO4
The ratio indicates the number of water molecules bonded to CuSO4
Name the hydrate using the correct prefix

36. Practice Problem
A hydrate is found to have the following percent composition: 48.8 % MgSO4 and 51.2% H2O. What is the formula and name for this hydrate?