CHEM 121 Chapter 5 1

The Mole 12 eggs = 12 bagels = 6.02 x hydrogen atoms = 6.02 x water molecules = 2 How many water molecules are in 3.5 moles of water?

Moles of Elements in a Formula How many moles of each element are in 1 mole of water? How many moles of each element are in 1 mole of glucose? 3

Molar Mass 4 Examples: Carbon Atomic mass? Molar mass? Water Molecular mass? Molar mass?

Calculations with Molar Mass You measure out 10.0 g of water. How many moles of water do you have? 5 If a piece of metal displaces 2.2 mL water, how many water molecules has it displaced? (Assume the density of water is 1.0 g/mL.)

Chemical Equations Physical Change: Chemical Change: Chemical Equation: 6

Types of Reactions 7 Mg OO + A B +

Types of Reactions 8 O HH B A

9 B A + C B A + C D

Chemical Equations _____________ and ___________ involved in change Ex. Reaction of magnesium solid and oxygen 10

Reaction Equivalents C 3 H 8 (g) + 5 O 2 (g)  3 CO 2 (g) + 4 H 2 O (g) 1 molecule C 3 H 8 reacts with _______ molecules O 2 1 molecule C 3 H 8 produces _______ molecules CO 2 1 molecule C 3 H 8 produces _______ molcules H 2 O 5 molecules O 2 produces _______ molecules CO 2 2 molecules C 3 H 8 produces _______ molecules CO 2 11

Ionic Equations Molecular equations – Total ionic equations – Net ionic equations – Example: HCl and NaOH

Precipitation Reactions Type of replacement reaction Example: Aqueous sodium iodide and lead (II) nitrate 13

Stoichiometry the study of mass relationships in chemical equations Can’t compare mass to mass Go to moles first 14

Reaction Calculations

Sample Problem How much carbon dioxide (in grams) is produced when 3.00 g of ethanol (C 2 H 6 O) combusts in air? How much oxygen gas is used up to combust 5.00 g of ethanol? 16

5-minute review How many grams of oxygen are needed to react with 1 mole of CH 4 to create water? Hint: carbon dioxide is also a product. 17

Yields Theoretical yield: Actual yield: – Percent yield: 18

Limiting Reactants What if we have: 8 scoops of ice cream 6 cherries 100 mL of syrup. How many sundaes can we make? 19

Chemical Reactions Involving a Limiting Reactant hydrazine (N 2 H 4 ) and dinitrogen tetraoxide are liquids that ignite to form nitrogen gas and water vapor How many grams of nitrogen gas form when 100. g of N 2 H 4 and 200. g of dinitrogen tetraoxide are mixed? 20

Redox Reactions Reduction and oxidation Movement of e- from one reactant to another 2 Mg (s) + O 2 (g) --> 2 MgO (s) LEO GER Reducing agent? Oxidizing agent? 21

Oxidation Numbers (O.N.) Any element has O.N. = 1A(1) ions = 2A(2) ions = H ion can only = Oxygen ion only = Halogen ions usually = The sum of all atoms O.N. in a compound = Examples: ZnCl 2 sulfur trioxide potassium sulfate 22

3-minute review What is the O.N. of each atom in CaCO 3 ? 23

Redox Reaction? CaO (s) + CO 2 (g) → CaCO 3 (s) 24

3-minute Review What’s been oxidized in each reaction? Cu (s) + AgNO 3 (aq) → Ag (s) + Cu(NO 3 ) 2 (aq) N 2 (g) + H 2 (g) → NH 3 (g) 25