Quiz this Friday

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Quiz this Friday
Table similar to questions 49 and 50 on page
71 Naming of compounds
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Ch 3. Stoichiometry
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isotopes same of protons, different of
neutrons
mass of a proton mass of a neutron gtgt mass of
an electron
number of protons number of neutrons mass
number
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Figure 3.1 (left) A Scientist Injecting a Sample
into a Mass Spectrometer. (right) Schematic
Diagram of a Mass Spectrometer
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Figure 3.3 Mass Spectrum of Natural Copper
69.09 63Cu 30.91 65Cu
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1H 1.6735 x 10-24 g 16O 2.6560 x 10-23 g
One atomic mass unit (amu) is defined as 1/12
of the mass of a 12C atom.
12C atom 6 protons, 6 neutrons, 6 electrons.
1 amu 1.6605 x 10-24 g
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1H 1.6735 x 10-24 g 16O 2.6560 x 10-23 g
1 amu 1.6605 x 10-24 g
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35Cl 34.967 amu 37Cl 36.966 amu
75.78 24.22
How to find the average?
1, 1, 1, 1, 2
Average (1 1 1 1 2) / 5 1.2
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35Cl 34.967 amu 75.78 37Cl 36.966 amu 24.22
Average atomic mass of Cl 34.967 amu x
75.78 36.966 amu x 24.22 35.451 amu
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Figure 3.3 Mass Spectrum of Natural Copper
69.09 63Cu 62.93 amu 30.91 65Cu 64.93
amu
Average atomic mass of Cu ?
12
mass of a proton mass of a neutron 1 amu
mass number of an isotope atomic mass of
the isotope in amu
35Cl 34.967 amu 75.78 37Cl 36.966 amu 24.22
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One atomic mass unit (amu) is defined as 1/12
of the mass of a 12C atom.
The number of carbon atoms in exactly 12 g of
12C is called Avogadros number 6.022 x 1023
One Avogadros number of particles is called a
mole.
1 mol 6.022 x 1023 particles
1 pair 2 particles 1 dozen 12 particles
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For an element X, its atomic mass is x amu. What
is the mass of 1 mol of X in grams?
The mass of 1 mol of X is x g.
The molar mass of an element is the mass in
grams per mole of the element.
Unit g/mol
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Two ways to find molar mass
1) Read from the periodic table
(recall d m/V)
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1 mol 6.022 x 1023 particles
Unit g/mol
identity of element ? read molar mass from
periodic table
molar mass and Avogadros number are exact numbers
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Sample exercise 3.2, page 83
Compute the mass in grams of a sample of
six Americium atoms.
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Sample exercise 3.4, page 85
A silicon chip has a mass of 5.68 mg. How many
silicon atoms are present in the chip?
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Sample exercise 3.5, page 85
Calculate the number of moles in a sample of
cobalt (Co) containing 5.00 x 1020 atoms and the
mass of the sample.
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Plan for this weeks problem solving session
Comments on lab report. Bring your graded report.
Question 49 on page 71. Naming on page 72
73 55, 56 a, b, e, f 61 c, d 70 a to
e 57 a, c, e 62 a, b 58 a, b, c 63 a
to e 59 a, b 64 g to l 60 a, b 66 all
Make-up quiz 2.
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Sample exercise 3.6, page 86

• Juglone C10H6O3
• What is the molar mass of juglone?
• How many moles are in a sample of 1.56 x 10-2 g
  of
• juglone?
• c) How many moles of C, H, and O are in this
  sample?

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Sample exercise 3.7, page 86 - 87

• Calcium carbonate CaCO3
• Calculate the molar mass of CaCO3.
• A sample of CaCO3 contains 4.86 mol. What is the
  mass
• of this sample? What is the mass of the CO32-
  ions present?

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Sample exercise 3.8, page 88
Sample 1 µg of isopentyl acetate (C7H14O2). How
many molecules are in this sample? How many C
atoms are in this sample?
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Two ways to describe the composition of a compound
Chemical formula
Mass percent of each element
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What is the mass percent of H in HCl?
2.765
Pick exactly 1 mol of compound to calculate.
What is the mass percent of H in CH4?
25.13
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What is the mass percent of nitrogen in ammonium
nitrate?
NH4NO3
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Chemical formula
Mass percent of each element
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Example on page 92
A compound contains 38.67 C, 16.22 H and
45.11 N. What is its chemical formula?
Pick exactly 100 g of compound to calculate.
If the molar mass of this compound is 62.12
g/mol, what is its molecular formula?
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Empirical formula formula of a compound showing
the simplest whole number ratio of the atoms in
the compound. Molecular formula formula of a
compound showing the exact number of each type of
atom in a molecule of the compound.
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Sample exercise 3.12, page 94
A compound contains 43.64 of P and 56.36 of
O. What is its empirical formula? If its
molar mass is 283.88 g/mol, what is the molecular
formula?
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Sample exercise 3.12, page 95
Caffeine contains 49.48 C, 5.15 H, 28.87 N,
and 16.49 O by mass and has a molar mass of
194.2 g/mol. Determine the empirical and
molecular formulae.
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In a chemical reaction, Old chemical bonds are
broken and new chemical bonds are formed. Atoms
are neither created nor destroyed. Mass is
conserved.
Chemical Equation Reactants ? Products
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CH4 O2 ? CO2 H2O
2
2
Each chemical has a certain composition (formula).
We must balance each chemical equation.
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CH4 2O2 ? CO2 2H2O
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Conversion to simplest integer ratio
1.000 2.002 2.998 1 2 3
1.000 2.499 3.001 1 2.5 3 10 25 30
2 5 6
1 2.4 3 10 24 30 5 12 15
0.333 1.667 2.001 1.000 5.006 6.009
1 5 6
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CH4 2O2 ? CO2 2H2O
Specify the physical states of the reactants and
products s solid, l liquid, g gas, aq in
aqueous solution
CH4 (g) 2O2 (g) ? CO2 (g) 2H2O (g)
How to balance a chemical equation?
Start from the most complicated chemical, adjust
the coefficients of others. Make all
coefficients integers.
Examples
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CH4 (g) 2O2 (g) ? CO2 (g) 2H2O (g)
Stoichiometry of the reaction
FIXED ratio for each reaction
Can calculate how much other chemicals are
required or produced if the amount of one
chemical is known.
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CH4 (g) 2O2 (g) ? CO2 (g) 2H2O (g)
2 mol
4 mol
2 mol
4 mol
3 mol
6 mol
3 mol
6 mol
5.22 mol
10.44 mol
5.22 mol
10.44 mol
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4 NH3 (g) 5 O2 (g) ? 4 NO (g) 6 H2O (g)
3.02 mol of NH3 is used in the above reaction.
How many moles of O2 is required to react with
all the NH3? How many moles of H2O will be
produced?
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2NH3(g) 3CuO(s) ? N2(g) 3Cu(s) 3H2O(g)
2 mol
3 mol
1 mol
3 mol
3 mol
5.02 mol
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Sample exercise 3.16, page 105
Solid lithium hydroxide is used in space vehicle
to remove exhaled carbon dioxide from the living
environment by forming solid lithium carbonate
and liquid water. What mass of gaseous carbon
dioxide can be absorbed by 1.00 kg of lithium
hydroxide?
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2NH3(g) 3CuO(s) ? N2(g) 3Cu(s) 3H2O(g)
2 mol
3 mol
1 mol
3 mol
3 mol
6.04 g
6.04 g (14.01 g/mol x 1 1.008 g/mol x 3)
0.355 mol
0.355 mol
Mass of CuO 0.533 mol x 79.55 g/mol 42.4 g
Mass of N2 0.178 mol x 28.02 g/mol 4.99 g
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Sample exercise 3.17, page 105
Baking soda (NaHCO3) is often used as an antacid.
It neutralizes excess hydrochloric acid secreted
by the stomach
NaHCO3 (s) HCl (aq) ? NaCl (aq) H2O (l) CO2
(aq)
Milk of magnesia, which is an aqueous suspension
of magnesium Hydroxide, is also used as an
antacid
Mg(OH)2 (s) 2HCl (aq) ? 2H2O (l) MgCl2 (aq)
Which is the more effective antacid per gram,
NaHCO3 or Mg(OH)2?
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NaHCO3 (s) HCl (aq) ? NaCl (aq) H2O (l) CO2
(aq)
1.00 g
1.00 g 84.01 g/mol 0.0119 mol
x
0.0119 mol
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Mg(OH)2 (s) 2HCl (aq) ? 2H2O (l) MgCl2 (aq)
1.00 g
1.00 g 58.32 g/mol 0.0171 mol
y
0.0171 mol
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NaHCO3 (s) HCl (aq) ? NaCl (aq) H2O (l) CO2
(aq)
1.00 g
x 0.0119 mol
Mg(OH)2 (s) 2HCl (aq) ? 2H2O (l) MgCl2 (aq)
1.00 g
y 0.0342 mol
Mg(OH)2 is the more effective antacid per gram.
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CH4 2O2 ? CO2 2H2O
The actual amount of reactants consumed and
actual amount of products generated agree with
the stoichiometry.
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CH4 2O2 ? CO2 2H2O
x
0.5 mol
1 mol CH4 requires 2 mol O2, available O2 is 1
mol limiting reagent.
Result 1 mol O2 will be consumed completely and
CH4 will have leftover excess reagent.
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The reactant of which there are fewer moles than
the stoichiometry requires is the limiting
reagent.
The reactant of which there are more moles than
the stoichiometry requires is the excess reagent.
Chemical reactions always occur according to
the stoichiometry, therefore the limiting reagent
is consumed and the excess reagent has leftover.
The amount of products is determined by the
amounts of reagents that are actually consumed.
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limiting reagent
excess reagent
CH4 2O2 ? CO2 2H2O
0.5 1 0.5 1
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2 slices of bread 1 slice if ham ? 1 sandwich
4 slices of bread 1 slice if ham ?
1 sandwich 2 slices of bread
excess reagent
excess reagent leftover
limiting reagent
amount of product
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Sample exercise 3.18, page 95
For the following reaction, if a sample
containing 18.1 g of NH3 is reacted with 90.4 g
of CuO, which is the limiting reagent? How many
grams of N2 will be formed? 2NH3(g) 3CuO(s) ?
N2(g) 3Cu(s) 3H2O(g)
How many grams of excess reagent will be leftover?
If 6.63 g of N2 is actually produced, what is the
percent yield?
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Procedure for limiting/excess reagent
calculations aA bB ? cC dD

• Make sure the equation is balanced.
• Find the moles of each reactant
• moles mass in gram / molar mass
• 3) Pick up any reactant, say A, and use the
  stoichiometry to
• calculate the required amount of the other
  reactant B.
• Compare the required amount of B with the
  available
• amount of B.
• a) If required gt available, then B is the
  limiting reagent and A
• is the excess reagent.
• b) If required lt available, then B is the excess
  reagent and A
• is the limiting reagent.
• Use the amount of the limiting reagent and the
  stoichiometry
• to calculate the amount of any product and the
  amount of the
• excess reagent that has been consumed.
• Leftover excess reagent available - consumed
• If actual yield is given
• percent yield (actually yield / theoretical
  yield) x 100

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68.5 g CO reacts with 8.60 g H2 in the following
reaction. What is the limiting reagent? How
many grams of excess reagent is leftover? What
is the theoretical yield of CH3OH? If 35.7 g
CH3OH is actually produced, what is the
percent yield of CH3OH?
H2(g) CO(g) ? CH3OH(g)
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Procedure for limiting/excess reagent
calculations aA bB ? cC dD

• Make sure the equation is balanced.
• Find the moles of each reactant
• moles mass in gram / molar mass
• 3) Pick up any reactant, say A, and use the
  stoichiometry to
• calculate the required amount of the other
  reactant B.
• Compare the required amount of B with the
  available
• amount of B.
• a) If required gt available, then B is the
  limiting reagent and A
• is the excess reagent.
• b) If required lt available, then B is the excess
  reagent and A
• is the limiting reagent.
• Use the amount of the limiting reagent and the
  stoichiometry
• to calculate the amount of any product and the
  amount of the
• excess reagent that has been consumed.
• Leftover excess reagent available - consumed
• If actual yield is given
• percent yield (actually yield / theoretical
  yield) x 100

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1.50 g of ammonia reacts with 2.75 g of oxygen
gas to produce nitrogen monoxide and water.
NH3(g) O2(g) ? NO(g) H2O(g) a)
Balance the equation. b) What is the mass of
O2 in grams required by NH3? c) Which
reactant is the limiting reagent? d) How
many grams of NO will be produced in theory? e)
How many grams of H2O will be produced in
theory? f) How many grams of the excess
reagent remain unreacted? g) If only 1.80 g of
NO are produced, what is the percent yield?