1. The MOLE It’s a beauty mark… It’s a small furry garden pest…
No, wait… its how we count ATOMS!

2. The mass of 1 mole of a substance.
Molar Mass
The mass of 1 mole of a substance.

3. FORMULAS - review
MgCl2 The subscript is the number at the bottom of a formula. There is 1- Mg & 2 - Cl

4. Calculate the molar mass
Calculate the molar mass of 1 mole of magnesium chloride. (first you need a formula)

5. How to calculate molar mass
Identify the # of atoms of each element
Multiply # atoms by the atomic mass of that element. (round to 2 #’s after the decimal)
Add them all together
Grams (g) is the unit

6. MgCl2 Mg – 1 (24.31) = 24.31 Cl – 2 (35.45) = 70.90 or 95.21 g/mol
Molar Mass
MgCl2 Mg – 1 (24.31) = Cl – 2 (35.45) = or g/mol
1 mole MgCl2 =
95.21 g MgCl2

7. Calculate the molar mass: (you MUST write the formula correctly before answering) 1 mole of Ammonium phosphide 1 mole of Trinitrogen pentachloride

8. What is a percentage mean?
How is a percent calculated? What is the percentage of girls in the class? What is the percentage of students in Mrs. Muchnick’s class if she has 10 girls and 12 boys?

9. Percent Composition
The percent BY MASS of each element in a compound – divide the element’s total mass (part) by the molar mass (whole) then multiple by 100 to get the percent.
Ex: % composition of MgCl2
Mg – 1 (24.31) = / x 100 = % Mg
Cl – 2 (35.45) = / x 100 = % Cl
Molar mass = g/mol
(PART)
(WHOLE)
(PART)
(WHOLE)

10. Practice - Calculate the % comp of KMnO4:
K – 1 (39.10) = / x 100 = 24.74% K Mn – 1 (54.94) = / x 100 = 34.76% Mn O – 4 (16.00) = / x 100 = 40.50% O molar mass KMnO4 =

12. Calculating the amount of an element in a sample
Find the % comp of the element in the compound
Change the % to a decimal (move decimal 2 times to the left or divide by 100)
Multiply that decimal by the amount (g) of the sample.
Ex: Calculate amount of chlorine in grams of MgCl2. (use the % we found earlier)
74.47% Cl = x = grams Cl

13. Practice: Calculate the amount of oxygen in 15.75 grams of water.
H – 2(1.01) = 2.02 O – 1(16.00) = Molar mass H2O = 18.02
/ x100 = % O
88.79% O = x = grams O
Complete % comp worksheet

14. Empirical Formula
The lowest whole number ratio (subscripts) of elements in a compound.
Cannot be reduced!!!
not empirical empirical
Ex: C6H12O6  CH2O

15. Molecular Formula NO3 Actual number of atoms in a chemical compound
EX: C12H24O12
Molecular Formulas can be reduced to Empirical Formulas
molecular empirical
EX: C12H24O12  CH2O
Different molecular formulas can have similar empirical formulas
molecular empirical
EX: N3O 
N12O36 
Molecular formula: C76H52O46
Empirical formula: ___________
NO3

16. PRACTICE: 1. Identify each as empirical (can’t be reduced) or molecular (can be reduced) 2. If its molecular – write the empirical
C2H4
NO3
S9Cl12
C3Cl9
N4S9
CH2 - empirical
molecular
empirical
S3Cl4 - empirical
molecular
CCl3 - empirical
molecular
empirical

17. Finding Empirical Formula from Percent Composition
Ex: A compound was found to be 54.53% Carbon, 9.15% Hydrogen, and 36.32% Oxygen. Find its Empirical Formula.
Steps:
Assume a 100g sample (change %  g)
Use molar mass to find moles of each
Divide all moles by the smallest number of moles
Round each to the nearest whole # (sometimes you have to multiply to get a whole number - special)
The resulting whole #are the subscripts for that element in the empirical formula

18. Calculating Empirical Formula
63.5% Silver 8.2% Nitrogen 28.3% Oxygen 63.5 g Ag 8.2 g N 28.3 g O mole Ag .59 mole N 1.77 mole O AgNO3

19. Calculating Empirical Formula (special)
60.00%C 4.48%H 35.53%O 60.00g C 4.48g H 35.53g O mole C 4.44 mole H mole N x4 x4 x C9H8O4

20. Calculating Molecular Formula
Find the empirical formula
Calculate the molar mass of your empirical formula
Identify the molar mass of your molecular (GIVEN in the problem everytime!)
Divide the molecular mass / empirical mass
Round to the nearest whole #
Multiply the whole # by the subscripts in the Empirical formula

21. Practice
If a compound has an empirical formula of NO3 and a molecular mass of 186g – what is the molecular formula?
Empirical formula: NO molar mass: 62.01g
Molecular mass (given) g
empirical mass
3 x NO = N3O9

22. What is a mole?
For counting matter (quantity) in chemistry we use the mole
Moles are used to correctly measure chemicals for reactions in a lab.
Problem – no way to “physically” measure a mole. (no lab equipment measures moles)
Solution – molar mass (balance)

23. Using Molar Mass
Remember – Molar mass is the mass (grams) of 1 mole 1 mole Fe = _________grams Fe 2.5 mole Fe = ________ grams Fe grams Fe = _______ moles Fe Mass to mole = divide by molar mass Mole to mass = moletiply by mole mass 

24. Using molar mass
How many grams are in 15.7 mole MgCl2 How many moles are in 0.75 grams of silver? What is the mass of 30.7 mole water?

25. Using molar mass
In the lab, Mrs. Mathieson needs 2.57 moles of NaCl to do an experiment. How many grams would be needed to equal 2.57 moles of NaCl? After doing the experiment, Mrs. Mathieson has 1.02 moles of NaCl remaining – how many grams does that equal?

26. What is a mole?
For counting matter (quantity) in chemistry we use the mole
1 mole = 6.02 x representative particles (particles are very tiny)
This value is called Avogadro’s Number

27. What are REPRESENTATIVE PARTICLES?
ie. the smallest particle that retains chemical and physical properties
3 types depending on the compound:
Atoms: Single element
Molecules: covalent compound
Formula Units: Ionic Compounds or ions

28. Using Avagadro’s Number
Remember there are 6.02 x 1023 particles (atoms, molecule, f.u) in 1 mole
How many atoms are in 1 mole?
How many atoms are in 2.10 moles of Copper?
How many moles are in 4.21 x 1026 atoms of aluminum?

29. What is a mole?
For counting matter (quantity) in chemistry we use the mole
1 mole = 22.4 L of any gas
This value is called Molar Volume

30. Using molar volume
How many liters are in 1 mole of any gas? How many liters are in L of oxygen gas? How many moles are in moles of nitrogen gas?