1. CHAPTER 3
AP CHEMISTRY

2. AMU Atomic masses come from the carbon-12 scale
Mass of carbon-12 is exactly 12 amu
Nitrogen-14 has an amu of this is about 14/12 times heavier than carbon-12. C-12 is 12 times heavier than H-1
Isotopic abundance was proven in 1914
Relative masses of atoms can be determined by the mass spectrometer 1918

3. Ne %; Ne %; Ne %

4. Relative abundance of isotopes can be determined
by the mass spectrometer
CH3+
C2H3+
CH3CO-
C3H6O

5. For which compound does this mass spectrometer reading belong to?
a. C3H8 b. C2H6O c. NO d. N2O e. CO2

6. 6.02 X 1023 particles/ 1mole Molar mass molar volume 22.4L/1 mole MASS
VOLUME of gases at STP

7. EXAMPLE
The following example presents an extra challenge; we need to find the amount of carbon in CO2 and hydrogen in H2O.
In g sample of ascorbic acid, vitamin C, was burned in a carbon-hydrogen combustion apparatus to produce g CO2 and g of H2O. Ascorbic acid only contains carbon, hydrogen and oxygen. Determine the masses and then determine the simplest formula
remember find percent of carbon and hydrogen first
27.2%C and 11.1%H (change into decimal) times to the masses
.05084gC, gH subtract both from .1247
divide each by the elemental mass
mol O, mol H, and mol C
1C, 1.32H, and 1O times everything by 3
C3H4O3

8. MOLECULAR FORMULA
In order to obtain the molecular formula, we need to know the molar mass
Molar Mass = small whole number Simplest Formula mass
The simplest formula of nicotine which has been used in insecticides is C5H7N. From another experiment, the molar mass is found to be about 160 g/mol. What is the molecular formula of nicotine?
Add atoms mass
= 81.0
160/81 = 2
C10 H14 N2

9. TYPES OF REACTIONS COMBUSTION
Hydrocarbons with oxygen making carbon dioxide and water
C3H8 + O > CO2 + H2O balance this
Write a balanced equation for the reaction that occurs when ethanol, C2H5OH(l), is burned in air
COMBINATION OR COMPOSITION
Formation of a single product
Al(s) + O2(g) -----> Al2O3(s) balance this
DECOMPOSITION
A single reactant is broken down
CaCO3(s) ----> CaO(s) + CO2(g)

10. CONTINUE SINGLE REPLACEMENT DOUBLE REPLACEMENT
One element replaces another
Zn (s) + CuSO4(aq) >Cu (s) + ZnSO4(aq)
DOUBLE REPLACEMENT
Atoms or ions exchange partners
Ca(OH)2(aq) + HCl(aq) --> CaCl2(aq) + H2O(l) balance this

11. EXPERIMENTAL YIELD From the following reaction:
CS2(l) + 3O2(g) ----> CO2(g) + 2 SO2(g)
Determine the limiting reactant and the theoretical yield of the product SO2(g) if we have 105 g of CS2 and 145 g of O2.
Experimental yield; % yield
% yield = actual (experimental) yield X 100
Theoretical yield

12. CONTINUE
An ester was formed by heating 20.0 g of ethanol, C2H5OH(l), with excess acetic acid to yield 21.8 g of ethyl acetate, CH3COOC2H5. Calculate the % yield of ethyl acetate. (Water is also formed)