1. Counting Atoms: Equivalency Statements and THE MOLE!
Chapter 8

2. Equivalency Statements
An Equivalency Statement tells us how much of two or more groups are equal.
Examples
1 cm = 10 mm
1 dozen = 12 eggs
1 mile = 5280 ft
1 car = 4 wheels
1 spider = 8 legs

3. Equivalency Statements
Needed for conversions
1 nm = 10-9 m
1 mg = 10-3 g
1 cL = 10-2 L
1 Kcal = 103 cal
1 Megabyte = 106 bytes (roughly)

4. Using equivalency statements in conversions
Use the railroad method
Practice problems
How many Mg are there in x 105g
How many m are there in x 10-2 mm
How many leg are there on x spiders

5. Using equivalency statements in conversions
Use the railroad method
Practice problems
How many mcal are there in x kcal
How many nm are there in x 1025 km
How eggs are there in 34.5 x 103 dozen?

6. The Origin of the Mole
The mole is the ultimate equivalency statement for chemistry.
It allows us to use a.m.u. (atomic mass units) from the periodic table in conversion calculations
1 a.m.u. = mass of 1 proton
Question: How many atoms does it take to convert a.m.u. to grams?

7. Avogadro’s Number 6.022 x 1023 particles* = 1 mol
*Note: the word particles could be replaced by atoms, compounds, molecules, ions, or about anything else
Practice Problems
How many atoms are in 10 moles sulfur?
How many molecules are in 23.4 x 10-3 mol of CaCl2
How many ducks are in 3.4 x mol ducks

8. Practice 4. How many moles are 200.0 x 1025 atoms of Aluminum?
5. How many moles is 1 atom of Calcium?
6. How many Li+ ions are in 2 mol of Li2O
7. How many Cl- are in 3.03 x mol of AlCl3?

9. Mass to Mol conversions
Because Avogadro calculated the mole based on
1 proton = 1 amu this equivalency statement is correct:
Atomic mass (g) = 1 mol
We call this the MOLAR MASS (the amount of g/mol)
Write equivalency statements for the following: Al Be U

10. Mass to Mol conversions
6.94 g of lithium is how many moles?
790.1g of potassium is how many moles?

11. Mass to Mol conversions
x 103 g of oxygen is how many moles?

12. Mol to mass conversions
2.4 mol of Calcium has what mass?
230 mol of Uranium in how many grams?

13. Mol to mass conversions
How many Kg does 3.2 x 102 mol of sodium weigh?
Homework: Read chapter 8.3 and answer # 20, 21

14. Mass to particles
These are 2 step conversions, combining the mass to moles and the moles to particle conversions
How many atoms are in 3.92 g of hydrogen?

15. Mass to particles How many atoms are in 4.3 x 102g of krypton?
How many atoms are in g of iron?

16. Particles to mass Same thing, just the other way round.
4.53 x 1025 atoms of helium have what mass?

17. Particles to mass 5.2 x 102 atoms of argon have what mass?
How many kg does 8.43 x 1026 atoms of magnesium weigh?

18. Molar mass (gram molecular mass)
Molar mass is the grams a mole of substance weighs
Unit = g/mol
Yesterday we did this with elements, today we will add compounds to the mix.
What is the molar mass for:
Magnesium
Silicon
Xenon

19. Molar mass
To calculated the molar mass of a compound, add up its elements
What is the molar mass of:
H2O
MgCl2
Al2S3
Na3PO4
Al2(C4H4O6)3

20. Molar mass
To calculated the molar mass of a compound, add up its elements
What is the molar mass of:
H2O g/mol
MgCl g/mol
Al2S g/mol
Na3PO g/mol
Al2(C4H4O6) g/mol

21. Molar mass in calculations
Once you have the molar mass of the compound you can use it as a equivalency statement, just like yesterday.
How many moles are 0.41g of NaCl?
1 mol NaCl = = 58.44g / mol
Set-up railroad

22. Practice 23.5 g of CaCl2 is how many moles?
How many moles is 0.231g of Silver?

23. How much would 8.99 mol of Li2O weigh in grams?
How many grams would 4.5 mol of Oxygen gas (O2) weigh?
How many compounds is 3.5g of NaCl?

24. Moles and Liters
Moles can also be converted to Liters if the particle we are studying is a gas
The conversion only works if the gas is at STP (Standard Temperature and Pressure)
0 degrees C
1 atm
1 mol = 22.4 L

25. Mol/Liters practice
If you have 44.8 L of CO2 how many moles of gas are there?
A balloon contains 2.1 x 101 mol of Helium, how many Liters of gas are in the balloon?

26. Mol/Liters practice
A person has the lung capacity of 6.2 L, how many moles of air can they hold?
The Hindenburg contained 2 x 108 L of hydrogen gas (diatomic). When the Hindenburg exploded, how many grams of gas burned?