2. Chapter 10
The Mole

3. Dimensional Analysis Write the equivalence statement needed.
2. Find the appropriate conversion factor.
3. Set up the problem by writing the “given”
item first (including unit).
4. Write the conversion factor (from step 2).
5. Make sure the units cancel out.
6. Do the arithmetic to find the answer.

4. What is a MOLE?
1 mole = 6.02 x 1023 things
That is
602,000,000,000,000,000,000,000
things.
6.02 x 1023 is known as Avogadro’s number

5. Representative particles means ‘things’. For example:
Representative particles could be atoms.
Na atoms, K atoms, Ar atoms, S atoms…
Representative particles could be molecules.
H2O molecules, CO2 molecules,
H2 molecules, Cl2 molecules,….
Representative particles could be formula units.
NaCl, MgBr2, Al2O3, CuO, FeS…
Representative particles could be onions.

6. Converting Representative Particles into Moles.
How many moles of magnesium
is 1.25 x 1023 atoms Mg?
0.208 mol Mg
How many moles is 2.80 x 1024 atoms Si?
4.65 mol Si

7. Converting Moles to Representative Particles.
How many molecules are in 2.12 moles of propane?
1.28 x 1024 molecules propane.
How many molecules are in
1.14 moles of SO3?
6.86 x 1023 molecules SO3.

8. The atomic mass of an element expressed in grams is the mass of a mole of the element.
Example:
Atomic mass of C is amu.
1 mol C = grams C
Atomic mass of S is amu.
1 mol S = grams S
Atomic mass of Co is amu.
1 mol Co = grams Co

9. 1 mol of H2O = 2 H + 1 O
= 2(1.008 g) + 1( g)
= g
1 mol of CO2 = 1 C + 2 O
= 1( g) + 2( g)
= g
1 mol of PCl5 = ???
= g

10. Converting Mass to Moles (grams to mol).
How many moles are 176 g Na?
7.66 mol Na
How many moles are g B?
mol B
How many moles are 5.2 g H2O?
0.29 mol H2O

11. Converting Moles to Mass (mol to g).
What is the mass of 2.50 mol Iron(II) hydroxide?
What is the mass of 0.75 mol argon?
Find the mass of mol C20H42.
225 g Fe(OH)2
30. g argon
26.6 g

12. From the homework:
Molecular mass  The mass of 1 molecule (in amu)
Formula mass 
Molar mass 
The mass of 1 formula unit (in amu)
The mass of 1 mole (in grams)
Coming up…..
Molar volume 
The volume of 1 mole (in L)

13. Molecules, Moles, and Mass 1.200 x 1022 formula units of Fe2(CO3)3
How many formula units are in a sample of iron(III) carbonate which has a mass of g?
1.200 x 1022 formula units of Fe2(CO3)3
What is the mass of
2.1 x 1024 molecules of N2O?
150 g

14. Find the mass of
9.73 x 1023 molecules of H2O.
29.1 g
Find the number of formula units in a g sample of silver chloride.
2.563 x 1022 formula units of AgCl

15. At STP, 1 mol of any gas has a volume of 22.4L.
Avogadro’s Hypothesis: Equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
Standard temperature and pressure (STP):
0oC (273 K) and 1 atm (or kPa)
At STP, 1 mol of any gas has a volume of 22.4L.
1 mol gas = 22.4 L

16. Find the volume of 0.375 moles of O2 gas at STP.
What is the volume of 3.20 x 10-3 mol CO2 at STP?
At STP, find the moles of L H2 gas.
8.40 L O2 gas
L CO2 gas
8.93 x 10-3 mol H2 gas

17. Calculating Molar Mass from Density
(use Molar volume [ 1 mol = 22.4 L ] )
The density of a gaseous compound containing carbon and oxygen is found to be g/L at STP. What is the molar mass of the compound?
43.99 g/mol
What is the density of Krypton gas at STP?
3.741 g/L

18. Percent Composition Mass of element % mass of element = x 100
Mass of compound
% mass of element = x 100
Calculate the percent composition of K2CrO4.
(You will have 3 answers:
one for K, one for Cr and one for O.)
40.28% K; % Cr; % O

19. A compound is formed when 9.03 g Mg combines completely with 3.48 g N. What is the percent composition of this compound?
72.2% Mg; 27.8% N
Calculate the percent of nitrogen in NH4NO3.
35.00% N

20. Empirical Formula
Gives the lowest whole number ratio of the atoms of the elements in a compound.
Steps for determining empirical formulas.
Assume the entire sample has a mass of 100g.
Find the mass of each element in the compound using the percentages given.
Convert the mass of each element to moles.
Find the mole ratio for the elements.
Reduce to lowest whole number ratio.
Write the empirical formula.

21. Empirical Formula HO C3H8N
Gives the lowest whole number ratio of the atoms of the elements in a compound.
Find the empirical formula of a compound that contains 94.1% O and 5.9% H. HO
1,6-diaminohexane is used to make nylon. What is the empirical formula of this compound if it is 62.1%C, 13.8% H and 24.1% N?
C3H8N

22. Molecular Formula Is a multiple of its empirical formula.
Steps for determining molecular formulas.
Determine the empirical formula.
Calculate the molar mass of empirical formula using the periodic table.
Using the molar mass of the molecule (always given in the problem!!!), find n.
4. Multiply the subscripts in the empirical formula
by n to get the molecular formula.
Mass of molecular formula (GIVEN)
Mass of empirical formula
n =

23. Molecular Formula C2H8N2 C2H6O2
Find the molecular formula of a compound whose molar mass is 60.0 g/mol and empirical formula is CH4N.
C2H8N2
Find the molecular formula of ethylene glycol. The molar mass is 62.0 g/mol and the empirical formula is CH3O.
C2H6O2