Chapters 11

1
Chapters 11 12

• The Mole Stoichiometry

2
Dimensional Analysis

• Dimensional Analysis - a problem solving method
  that focuses on the units that are used to
  describe amount of matter.
• 1) How many minutes in 3 days?

3
Dimensional Analysis

• 2) How many centimeters in 8.0 inches?
• 3) How many inches in 5.25 meters?

4
Dimensional Analysis

• 4) How many goats can you buy if you have 3
  horses?
• 2 horses 3 cows
• 2 goats 1 cow

5
Mole Concept

• 1 dozen
• 1 mole

12
particles in 12 grams of carbon-12
6.02 x 1023
6
Mole Concept

• 1 mole of desks ___________ desks
• 1 mole of nails ___________ nails
• 1 mole of pens ___________ pens
• 1 mole people ________ people ________ hands
• 1 mole of carbon ______________ atoms
• 1 mole of water ____________ molecules
• 1 mole of carbon dioxide __________ molec.
• ____________ atoms

6.02 x 1023
6.02 x 1023
6.02 x 1023
6.02 x 1023
2 (6.02 x 1023)
6.02 x 1023
6.02 x 1023
6.02 x 1023
3 (6.02 x 1023)
7
Mole Wheel Problemsmoles ?? rep. particles

• How many atoms in 3.00 moles of carbon?
• How many moles in 3.57 x 1024 molecules of sugar?

8
Mole Wheel Problems moles ?? volume

• How much space (volume) would 5.5 moles of carbon
  dioxide occupy at STP?
• A sample of gas occupies 17.0 liters at STP. How
  many moles is this?

9
Mole Wheel Problems moles ?? mass

• Whats the mass of 0.125 moles of iron?
• Whats the mass of 1.1 moles of carbon dioxide?

10
Mole Wheel Problems multi-step problems

• A sample of oxygen gas has a mass of 85 grams.
  How many moles is this?
• Whats the mass of 15.0 L of carbon monoxide gas.

11
Mole Wheel ProblemsApplication Problems not
quite mole wheel

• How many moles of oxygen atoms in one mole of
  CO2? ____
• How many moles of oxygen atoms in three moles of
  sugar, C12H22O11? ____

12
Mole Wheel Problems Application Problems not
quite mole wheel

• How many moles of hydrogen in 1.5 moles of C2H6?
• How many atoms of hydrogen in 1.5 moles of C2H6?
• How many atoms in 1.5 moles of C2H6?

13
Mole Wheel Problems

• How many moles of Na ions in 1 mole of Na3PO4?
  ____
• A sample of sodium phosphate has a mass of 25.0
  grams. How many moles of Na ions?

14
Composition

• composition the percent mass of each element
  in a compound.
• H2O
• Ba(NO3)2

15
Empirical vs. Molecular Formula

• Molecular Formula
• Empirical Formula
• Exs

16
Empirical/Molecular Formulas

• Given
• 1) Convert to mass (Assume 100g.)
• 2) Convert mass to moles
• 3) Convert moles to simplest ratio (make
  whole s if necessary).

composition
mass composition
mole composition
17
Empirical/Molecular Formulas

• 1). A compound is found to be 41.9 sodium,
  19.1 phosphorus, and 38.9 oxygen. Determine
  the empirical formula.

18
Empirical/Molecular Formulas

• 2). A compound is found to be 82.8 carbon and
  17.2 hydrogen. Determine the empirical formula.

19
Empirical/Molecular Formulas

• Determining the molecular formula from
  experimental data
• 3) If the molar mass of the compound in 2 is
  58.0 g/mol, what must be the molecular formula?

20
Hydrate Formulas

• Determination of a hydrate formula
• 8.00 grams of hydrated barium hydroxide (Ba(OH)2
  x H2O) are heated. 4.35 grams remain after
  heating. What is the formula of this hydrate?

21
Easy Mole Ratios

• AgNO3 (aq) NaCl(aq) ? AgCl(aq) NaNO3 (aq)
• If 1 mole of AgNO3 reacts, ____ moles of NaCl are
  needed, ____ moles of AgCl and ___ moles of NaNO3
  are formed.
• Thus if 2 moles of AgNO3 react, ____ moles of
  NaCl are needed, ____ moles of AgCl and ___ moles
  of NaNO3 are formed.

22
Easy Mole Ratios

• 2 H2 (g) O2 (g) ? 2 H2O (g)
• If 2 mole of H2 react, ____ moles of O2 are
  needed, ____ moles of H2O are formed.
• If 4 mole of H2 react, ____ moles of O2 are
  needed, ____ moles of H2O are formed.

23
Easy Mole Ratios

• N2 (g) 3 H2 (g) ? 2 NH3 (g)

24
Limiting Reactants

• The KEY to understanding limiting reactants is to
  understand the meaning of a balanced chemical
  equation.
• Balanced chemical equation
• Represents the simplest ratio of reactants and
  products for a particular reaction.
• i.e. THE RECIPE

25
Limiting Reactants
Ammonia Recipe 1 molecule N2 3 molecule
H2 Yields 2 molecules NH3

• Brownie Recipe
• 1 egg
• ½ C. veggie oil
• 1 C. water
• Brownie mix
• Yields
• 9 x 13 pan
• 20 brownies

26
Limiting Reactants
Ammonia Recipe 1 mole N2 3 mole H2 Yields 2
moles NH3
Ammonia Recipe 1 molecule N2 3 molecule
H2 Yields 2 molecules NH3
OR
Which can be expressed as
N2 (g) 3 H2 (g) ? 2 NH3 (g)
27
Limiting Reactants
N2 (g) 3 H2 (g) ? 2 NH3 (g)
KEY This balanced equation tells you what RATIO
in which the elements react. NOT how much you
have/make of each.
28
Limiting Reactants
N2 (g) 3 H2 (g) ? 2 NH3 (g)

• If you have 2 moles of nitrogen and 3 moles of
  hydrogen.
• Does the balanced equation change?
• Do all of your reactants react?
• What, if anything remains?
• How much product can you make?

29
Limiting Reactants
Limiting reactant -
The substance that runs out first in a reaction
it thus LIMITS the amount of products that can be
formed
Excess reactant -
The substance that remains when the reaction is
complete i.e. its present in excess
30
Limiting Reactants
NaOH (aq) HCl (aq) ? H2O (l) NaCl (aq)

• If you have 3 moles NaOH and 4 moles of HCl
• Whats your limiting reactant?

31
Limiting Reactants
NaOH (aq) HCl (aq) ? H2O (l) NaCl (aq)
If you have 3 moles NaOH and 4 moles of HCl b.
How many moles of product will be formed?
32
Limiting Reactants
AgNO3 (aq) BaCl2 (g) ? 2 AgCl (s) Ba(NO3)2
(aq)

• If you have 5 moles silver nitrate and 3 moles of
  barium chloride
• Whats your limiting reactant?

33
Limiting Reactants
AgNO3 (aq) BaCl2 (g) ? 2 AgCl (s) Ba(NO3)2
(aq)
If you have 5 moles silver nitrate and 3 moles of
barium chloride b. How many moles of product
will form?
34
Limiting Reactants
AgNO3 (aq) BaCl2 (g) ? 2 AgCl (s) Ba(NO3)2
(aq)
If you have 5 moles silver nitrate and 3 moles of
barium chloride b. How many moles of excess
reactant remain?
35
Limiting Reactants
N2 (g) 3 H2 (g) ? 2 NH3 (g)

• If you have 2.5 moles of nitrogen and 6 moles of
  hydrogen.
• Whats your limiting reactant?

36
Limiting Reactants
N2 (g) 3 H2 (g) ? 2 NH3 (g)

• If you have 2.5 moles of nitrogen and 6 moles of
  hydrogen.
• How many grams of ammonia form?

37
Limiting Reactants
N2 (g) 3 H2 (g) ? 2 NH3 (g)

• If you have 2.5 moles of nitrogen and 6 moles of
  hydrogen.
• How many grams of excess reactant remain?

38
Percent Yield/ Percent Error

• Percent Yield compares the amt. of product you
  made to the amount of product you should have
  made.
• error actual yield x 100
• theoretical yield
• Percent Error tells by what percent you were
  off compared to what you should have made.
• error diff. between theoretical and actual
  yield x 100
• theoretical yield

39
Limiting Reactant Problems

• Given the following balanced equation CH4 2
  O2 ? CO2 2 H2O
• If 20.0 grams of methane is burned in 40.0 L of
  oxygen gas (_at_STP), how many grams of carbon
  dioxide will be formed?
• b. If 35.0 grams of carbon dioxide are produced,
  whats the percent yield and percent error?

40
Limiting Reactant Problems

• 50.0 g. of propane (C3H8) and 200. g. of oxygen
  react. Given the following balanced equation
• C3H8 5 O2 ? 3 CO2 4 H2O
• How many grams of water will be formed?

41
Limiting Reactant Problems

• 35.0 L of nitrogen and 6.72 g. of hydrogen react.
  Given the following balanced equation
• N2 3 H2 ? 2 NH3
• What mass of ammonia will be formed?