1. Molar Conversions & Calculations
Ch. 11 – The Mole

2. A. What is the Mole? VERY A large amount!!!!
A counting number (like a dozen)
Avogadro’s number (NA)
1 mol = 6.02  1023 items
A large amount!!!!
VERY

3. A. What is the Mole? HOW LARGE IS IT???
1 mole of hockey pucks would equal the mass of the moon!
1 mole of basketballs would fill a bag the size of the earth!
1 mole of pennies would cover the Earth 1/4 mile deep!

4. B. Molar Mass Mass of 1 mole of an element or compound.
Atomic mass tells the...
atomic mass units per atom (amu)
grams per mole (g/mol)
Round to 2 decimal places

5. B. Molar Mass Examples carbon aluminum zinc 12.01 g/mol 26.98 g/mol

6. B. Molar Mass Examples water sodium chloride H2O 2 atoms H + 1 atom O
2(1.01) = g/mol
NaCl
1 atom Na + 1 atom Cl
= g/mol

7. B. Molar Mass Examples sodium hydrogen carbonate sucrose NaHCO3
(16.00) = g/mol
C12H22O11
12(12.01) + 22(1.01) + 11(16.00) = g/mol

8. C. Percentage Composition
the percentage by mass of each element in a compound

9. C. Percentage Composition
Find the % composition of Cu2S.
g Cu
g Cu2S
%Cu =
 100 =
32.07 g S
g Cu2S
%S =
 100 =

10. C. Percentage Composition
Find the percentage composition of a sample that is 28 g Fe and 8.0 g O.
28 g
36 g
%Fe =
 100 =
8.0 g
36 g
%O =
 100 =

11. C. Percentage Composition
How many grams of copper are in a 38.0-gram sample of Cu2S?
Cu2S is % Cu
(38.0 g Cu2S)( ) = g Cu

12. C. Percentage Composition
Find the mass percentage of water in calcium chloride dihydrate, CaCl2•2H2O?
36.04 g g
%H2O =
 100 =

13. Practice
P. 322 #25; p. 331 #42, 43, 45
Answers on p. 929 and 930
P. 347 #111, 112; p. 348 #136

14. D. Molar Conversions molar mass 6.02  1023 MOLES (g/mol)IN
GRAMS
MOLES
NUMBER OF
PARTICLES
(g/mol)
(particles/mol)
“Particles”= atoms, electrons, molecules, formula units, anything!

15. D. Molar Conversion Examples
How many moles of carbon are in 26 g of carbon?
26 g C
1 mol C
12.01 g C
= mol C

16. D. Molar Conversion Examples
How many molecules are in 2.50 moles of C12H22O11?
6.02  1023
molecules
1 mol
2.50 mol

17. D. Molar Conversion Examples
Find the mass of 2.1  1024 molecules of NaHCO3.
2.1  1024
molecules
1 mol
6.02  1023
molecules
84.01 g
1 mol

18. Practice P.
Answers on p. 929 and 930

19. C2H6 CH3 E. Empirical Formula
Smallest whole number ratio of atoms in a compound
C2H6
reduce subscripts
CH3

20. E. Empirical Formula 1. Find mass (or %) of each element.
2. Find moles of each element.
-go out about 4 or 5 decimals
3. Divide moles by the smallest # to find subscripts.
4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #’s.

21. E. Empirical Formula Poem to help you remember… Percent to mass
Mass to mole
Divide by small
Multiply ‘til whole!

22. E. Empirical Formula
Find the empirical formula for a sample of 25.9% N and 74.1% O.
25.9 g
1 mol
14.01 g
= mol N
mol
74.1 g
1 mol
16.00 g
= mol O

23. N2O5 N1O2.5 E. Empirical Formula
Need to make the subscripts whole numbers
 multiply by 2
N2O5

24. CH3 C2H6 F. Molecular Formula
“True Formula” - the actual number of atoms in a compound
CH3
empirical
formula ?
C2H6
molecular
formula

25. F. Molecular Formula 1. Find the empirical formula.
2. Find the empirical formula mass.
3. Divide the molecular mass by the empirical mass.
4. Multiply each subscript by the answer from step 3.

26. F. Molecular Formula
The empirical formula for ethylene is CH2. Find the molecular formula if the molecular mass is g/mol?
empirical mass = g/mol
28.1 g/mol
14.03 g/mol =

27. G. Hydrates
Compounds with a certain number of water molecules attached
MgSO4·7H20 = magnesium sulfate heptahydrate
Use a prefix to indicate number of water molecules
MgSO4 without water is called anhydrous

28. G. Hydrates
To determine the number of water molecules, find the mole ratio of the anhydrous compound to the water
Find the moles of each
Set up a ratio: moles water/moles salt
Whole number answer is the number that goes in front of H2O

29. G. Hydrates
A 5g sample of a hydrate of Cu(NO3)2 was heated, and only 3.9g of the anhydrous salt remained. What is the formula and name of the hydrate?
Step 1: determine moles of the salt and the water
3.9g Cu(NO3)2 x 1mole = 0.02mol Cu(NO3)2
5g-3.9g=1.1g water
1.1gH2O x 1mole = .06mol H2O
18.02g

30. Step 2: determine ratio Step 3: formula and name
Moles H2O/moles Cu(NO3)2
0.06 mol H2O/0.02 mol Cu(NO3)2 =
Step 3: formula and name
Cu(NO3)2·3H2O
Copper (II) nitrate trihydrate