Transcript CHEM 5013 Applied Chemical Principles

CHEM 5013
Applied Chemical Principles
Chapters Three and Four (Mole Concepts)
Professor Bensley
Alfred State College
Chapter Objectives
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Explain the concept of a mole in your own
words.
Interpret chemical equations in terms of
both moles and molecules.
Interconvert between mass, number of
molecules, and number of moles.
Determine a chemical formula from
elemental analysis (i.e., from %
compositions).
Chapter Objectives
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Define the concentration of a solution and
calculate the molarity of solutions from
appropriate data.
Calculate the molarity of solutions prepared by
dilution or calculate the quantities needed to
carry out a dilution to prepare a solution of a
specified concentration.
Calculate the amount of product expected
from a chemical reaction, given the
amounts of reactants used.
Chapter Objectives
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Calculate the amounts of reactants
needed in a chemical reaction to produce
a specified amount of product.
Identify a limiting reagent and calculate
the amount of product formed from a
nonstoichiometric mixture of reactants.
Calculate the percentage yield of a
chemical reaction.
Molecular Weight
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Remember atomic weight?
Molecular Weight –
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Expressed in amu
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Example: H2O
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Formula Weight
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Formula weight:
Formula weight (FW) covers both ionic
and molecular compounds
NaCl: FW =
Examples
Calculate the formula weight of the
following compounds to 3 sig figs:
1.
Calcium hydroxide
2.
Methylamine CH3NH2
The Mole
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A mole is:
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A.
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B.
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C.
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D.
A chemical mass unit, defined
to be 6.022 x
23
10
molecules,
atoms, or some other unit.
The Mole
You have one car.
How many engines do you have?
How many wheels do you have?
You have 1 dozen cars.
How many engines do you have?
How many dozens of engines do you have?
How many wheels do you have?
How many dozens of wheels do you have?
12 x
You have 1 mole of cars. (1 Chemist’s Dozen)
6.02 x 1023 x
How many engines do you have?
How many moles of engines do you have?
How many wheels do you have?
How many moles of wheels do you have?
The Mole
You have one molecule of CCl4.
How many Carbon atoms do you have?
How many Chlorine atoms do you have?
You have 1 dozen molecules of CCl4.
How many Carbon atoms do you have?
How many dozen Carbon atoms do you have?
How many Chlorine atoms do you have?
How many dozen Chlorine atoms do you have?
12 x
You have 1 mole of CCl4. (Chemist’s Dozen)
6.02 x 1023 X
How many Carbon atoms do you have?
How many moles of Carbon atoms do you have?
How many Chlorine atoms do you have?
How many moles of Chlorine atoms do you have?
The Mole
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Example: One mole of Na2CO3 contains
how many moles of Sodium ions? How
many actual sodium ions?
How many moles of carbonate ions? How
many actual carbonate ions? Think of it as
(CO3)1
The Mole
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1 Mole of Oxygen atoms (O) contains how
many O atoms?
But 1 mole of Oxygen molecules (O2)
contains how many O atoms?
Molar Mass
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Molar mass:
What is molar mass of carbon-12? How many
grams in one mole?
Molar mass in grams per mole is numerically
equal to the formula weight in amu.
Examples
How many molecules of HNO3
are present in 2.5 moles
HNO3?
What is the mass in grams of
one nitric acid molecule, HNO3?
Mole Calculations
Two VERY important mole calculations:
1.
2.
How much does a given number of moles
of a substance weigh?
 (convert moles to grams)
Also, how many moles are in a given
mass of a substance?
 (convert grams to moles)
Mole Calculations
A sample of nitric acid contains 0.253
mol HNO3. How many grams is this?
A mixture for an acid used on a
construction project calls for 25 grams
of Sulfuric Acid (H2SO4) to be used.
How many moles of sulfuric acid is this?
Mole Calculations
The formulation for a test batch of
structural steel contains 0.05% Silicon
by mass. This calculates out to
1.0x10-6 gram for your formulation.
How many atoms of Silicon were
added to the batch to produce the
correct steel formulation?
Determining Chemical Formulas
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Percent composition of a compound =
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Mass percentage:
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# grams of A in 100 g of the whole thing
mass of A in the whole
Mass %A = 100 x
mass of the whole
Example
Lead(II) chromate, PbCrO4 is used
as a paint pigment (yellow).
What is the percentage
composition of lead(II) chromate?
Example
The chemical name of table sugar
is sucrose, C12H22O11. How many
grams of carbon (C) are there in
61.8 grams of sucrose?
Determining Chemical Formulas
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Empirical formula:
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Example: H2O2
Example
Sodium pyrophosphate is used in
detergent preparations. The
mass percentages of the elements
in this compound are 34.6% Na,
23.3% P, 42.1% O. What is the
empirical formula of sodium
pyrophosphate?
Molecular Formula from Empirical
Formula
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Molecular formula:
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Need 2 things to determine MF:
Molecular weight = n x empirical formula weight
So,
n=
molecular weight
empirical formula weight
Example
Hexamethylene is one of the
materials used to produce a type
of nylon. Elemental analysis of
the substance gives 62.1% C,
13.8% H and 24.1% N. Its
molecular weight is 116 amu.
What is its molecular formula?
Stoichiometry
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Definition:
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Based on:
Stoichiometry
N2 (g) + 3H2 (g)  2NH3 (g)
N2 molecules react with
H2 molecules to produce
NH3 molecules
of N2 reacts with
of H2 to produce
of NH3
Stoichiometry
N2 (g) + 3H2 (g)  2NH3 (g)
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Because moles can be converted to
grams, can also say:
How many grams of nitrogen will react
with 6.0 grams of hydrogen?
Stoichiometry
The number of moles involved
in a reaction is proportional to
the coefficients in the
balanced chemical equation!!!
Example
N 2 (g)  3H 2 (g)  2 NH 3 ( g )
How many moles of NH3 could we obtain from 3
moles of H2?
How many moles of NH3 could we obtain from 4.8
mol H2?
Stoichiometry
Can also calculate problems involving
masses of reactants or products
N2 (g) + 3H2 (g)  2NH3 (g)
How much hydrogen (in kg) is needed to
yield 907 kg of ammonia?
Grams of A
X
Flow Chart for
ANY
Stoichiometry
Problem
Conversion Factor:
grams A to mol A
X
Conversion Factor:
mol A to mol B
X
Conversion Factor:
mol B to grams B
Grams of B
Example
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How many grams of HCl are required to
react with 5.00 grams of manganese
dioxide according to the equation?
4 HCl(aq)  MnO 2 (s )  2 H 2O(l)  MnCl 2 (aq)  Cl 2 ( g )
Limiting Reagent
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What happens when we don’t exactly
follow the recipe?
Limiting reagent –
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What happens when the L.R. is used up?
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So what determines the number of moles
(amount) of product that we can obtain in
a reaction?
Limiting Reagent
100 seats and 300 tires. How many bicycles
can you make?
1 seat + 2 tires  1 bicycle
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The
are the limiting reagent
Limiting Reagent
Zn(s)  2 HCl(aq)  ZnCl 2 (aq)  H 2 ( g )
If 0.30 mol Zn is added to hydrochloric
acid containing 0.52 mol HCl, how many
moles of H2 are produced?
Limiting Reagent
Urea, CH4N2O, is used as a nitrogen
fertilizer. It is manufactured from
ammonia and carbon dioxide.
2NH3 + CO2  CH4N2O + H2O
10.0g NH3 and 10.0g CO2 are reacted
together. What is the maximum quantity
(in grams) of urea than can be obtained?
Theoretical Yield
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Theoretical yield:
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Percentage yield:
actual yield
%Yield 
 100%
theoretical yield
Working with Solutions
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Molar concentration or Molarity
Molarity (M) =
Moles of solute
Liters of solution
Molarity
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0.200 M (0.200 molar) solution of HCl is
how many moles of HCl dissolved in 1 liter
of water? How many grams of HCl
dissolved in 1 liter of water?
Example:
You place a 1.53 gram sample of potassium
dichromate, K2Cr2O7, into a 50.0 mL
volumetric flask and add water to bring the
solution up to the mark on the neck of the
flask. What is the molarity of the solution?
Example
A solution of sulfuric acid (H2SO4) has a
concentration of 0.154 M.
How many moles of sulfuric acid are
contained in a 500 mL bottle of the
solution?
How many grams of sulfuric acid are in the
500 mL solution?
Diluting Solutions
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You have a 10 M solution of
HCl.
Suppose however, you want
a 1 M solution.
How do we make this 1 M
solution of HCl?
Dilution formula derivation
Diluting Solutions
A stock solution of concentrated hydrochloric
acid is 12.1M. How much of this stock
solution is needed to prepare 1.00 L of an
aqueous solution, which is 0.25M HCl?