1. Unit #3 CDA Review Material

2. 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

3. 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.
Example – Find the % composition of MgCl2
(Using the info from molar mass on the previous slide Molar mass = g/mol)
Mg / x 100 = % Mg
Cl / x 100 = % Cl
(PART)
(WHOLE)

4. Percent of an element in a compound
Taking the % OF an amount
Change the percent to decimal (move 2x to left)
Multiply that decimal by the given amount
What is the mass of chlorine in 27.8g of MgCl2
(Use the % of Cl you just found on the previous slide)
74.47% Cl
x 27.8g = g Cl

5. ~ Empirical (CANNOT be reduced) ~ Molecular (CAN be reduced)
Identifying Empirical & Molecular Formulas
~ Empirical (CANNOT be reduced) ~ Molecular (CAN be reduced)
C2H4
NO3
S9Cl12
C3Cl9
N4S9
CH2 - empirical
molecular
empirical
S3Cl4 - empirical
molecular
CCl3 - empirical
molecular
empirical

6. Calculating Empirical Formula (% comp  empirical formula)
Change %  g for each element
Divide by molar mass of that element
Identify the smallest number of moles and divide all by that number
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

7. Calculating Empirical Formula
63.5% Silver % Nitrogen % Oxygen
63.5 g Ag 8.2 g N g O
.589 mole Ag .59 mole N mole O
AgNO3

8. 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 every time!)
Divide the molecular mass / empirical mass
Round to the nearest whole #
Multiply the whole # by the subscripts in the Empirical formula

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

10. Mole Conversions

11. Mole Conversions
1 mole = molar mass (grams) 1 mole = 6.02 x 1023 particles (atoms, molecules, fu) 1 mole = 22.4 Liters

12. 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?

13. 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?

14. 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?