Download Ch. 6 packet - Mahtomedi High School

1. What is the mass, in grams, of each of the following?
a. 1.0 mol Li
6.9 g Li
b. 2.0 mol Al
54 g Al
c. 6.50 mol Cu
413 g Cu
d. 6.02 X 1023 atoms of Ag
e. 2.57 X 1023 atmos of S
108 g of Ag
Atoms ­­> moles ­­> grams
0.0137 g S
2. How many moles of atoms are represented by each of the following?
a. 40.1 g Ca
1.00 mol Ca
b. 5.87 g Ni
0.100 mol Ni
c. 2.65 g Fe
0.0475 mol Fe
d. 2.24 X 1025 atoms of Zn
e. 50 atoms of Ba
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Determine the number of atoms contained in each of the following
a. 5.40 g B
3.01 X 1023 atoms of B
b. 8.02 g S
1.56X1023 atoms S
c. 1.50 g K
Calculate the molar mass of the following compounds
1. H2O
18.O g/mol
2. NH3
17.O g/mo1
3. C6H12O6
180.O g/mol
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4. Mg(OH)2
58.3g/mo1
5. Al2(SO4)3
342.3 g/mol
6. Ca(NO3)2
164.1g/mol
Find the weight of each of the following expressed in grams
a. 2.00 moles of carbon tetrachloride
b. 0.25 mole of Ca(OH) 2
c. 4.1 mol of H 2O
d. 1.50 mole of HC 2H3O2
e. 5.3 X 10 24 molecules of silver nitrate
f. 2.2 X 10 20 molecules of CO2
Give the correct number of moles of a substance
a. 25.0 grams of CaCO 3
b. 22.0 grams of carbon dioxide
c. 120.3 grams of calcium nitrate
d. 156 grams of Li2S
e. 3.40 X 1023 molecules of H2O2
f. 4.80 X 1023 moleucules of methane, CH4
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Chapter 6 Notes Packet
Name:
Hour:
6.1 Counting By Weighing
Counting by weighing is useful when measuring ___________ quantities of a substance.
Examples:
a)
The average mass of one M & M is 4 grams. How much would 54 M & M‛s weigh?
b)
How many M & M‛s are in 88 grams of the candy?
6.2 Atomic Masses: Counting Atoms by Weighing
The atomic masses found on the periodic table are __________ atomic masses for all of the ____________
of the elements. Elements masses are measured in ________. These masses can be used to make conversions
in chemistry.
Example:
a)
Calculate the mass in amu of 25 lead atoms.
b)
Calculate the number of Helium atoms in a sample that has a mass of 24 amu.
6.3 The Mole
In section 6.3 we used _________ for mass, but these are extremely ___________ units. In the lab a much
larger unit, the _________, is the convenient unit for ____________.
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Assume we have a sample of carbon that has a mass of 12.01. What mass of What mass of nitrogen has
exactly the same number of atoms as the sample of carbon?
If we weigh out samples of all the elements to have a mass equal to that element‛s average atomic mass in
grams, all of the elements would contain the same number of atoms. This number would be
___________________, which is called a _______ in chemistry. This number is called __________ number
for the scientist who discovered it.
This information has given us two conversion factors that we will use. The first conversion factor is that the
atomic mass in grams , which can be found on the __________________________ is equal to 1 mole.
_______ g = 1 mol
The mass in grams changes depending on which atom you are measuring. For example the conversion factor
for aluminum would be ______ g = 1 mole.
The other conversion factor is Avogadro‛s Number. This conversion never changes. __________________
atoms = 1 mole.
Example 1: What is the mass in grams of 3.50 mol of the element copper (Cu)?
Example 2: A chemist produced 11.9 g of aluminum. How many moles of aluminum have been produced?
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Example 3: How many moles of silver are in 3.01 x 1023 atoms?
1. What is the mass, in grams, of each of the following?
a. 1.0 mol Li
b. 2.0 mol Al
c. 6.50 mol Cu
d. 6.02 x 1023 atoms Ag (You will need to use both conversion factors!)
e. 2.57 x 1020 atoms S
2. How many moles of atoms are represented by each of the following?
a. 40.1 g Ca
b. 5.87 g Ni
c. 2.65 g Fe
d. 2.24 x 1025 atoms Zn
e. 50 atoms Ba
Title: Mar 6 ­ 1:19 PM (9 of 15)
3. Determine the number of atoms contained in each of the following (Use both conversion factors!)
a. 5.40 g B
b. 8.02 g S
c. 1.50 g K
6.2 Molar Mass
A compound is composed of more than one type of atom. The ________ mass is the mass in grams of one
mole of a compound . To find the molar mass of a compound we add up the atomic masses, in ___________, of
all of the atoms in the compound. For example, the compound CO2 would have a molar mass of 44 g because
carbon has a mass of 12 g and oxygen has a mass of 16 g. We need to add the mass of two oxygen atoms, since
there are two oxygen atoms in the formula. Molar masses give us a conversion factor that we can use for
conversions between moles and grams. The number is different depending on the formula of the compound.
_______ g = 1 mole
Calculate the molar mass of the following compounds
1.
H2O
4. Mg(OH)2
2.
NH3
5. Al2(SO4)3
3. C6H12O6
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6. Ca(NO3)2
Calculations Using Molar Mass
Example 1: Calculate the mass of 1.48 mol of K2O.
Example 2: Calculate the number of moles in 2.4 g of H2O.
Example 3: Calculate the number of molecules in 3.2 g of CO2.
(Conversion Factor: 1 mole = 6.02 x 1023 molecules)
Perform the following calculations
1.
Find the weight of each of the following expressed in grams.
[a] 2.00 mole of carbon tetrachloride
[b] 0.25 mole of Ca(OH)2
[c] 4.1 mole of H2O
[d] 1.50 mole of HC2H3O2
[e] 5.3 x 1024 molecules of silver nitrate
[f] 2.2 x 1020 molecules of CO2
Title: Mar 6 ­ 1:20 PM (11 of 15)
2. Give the correct number of moles of a substance.
[a] 25.0 grams of CaCO 3
[b] 22.0 grams of carbon dioxide
[c] 120.3 grams of calcium nitrate
[d] 156 grams of Li 2S
[e] 3.40 x 1023 molecules of H 2O2
[f] 4.80 x 1023 molecules of methane, CH 4
6.5 Percent Composition of Compounds
Percent composition looks at the compounds composition in terms of the ____________ of its elements. The equation
for mass percent is. . .
Mass Percent of Element = mass of element in compound
Mass of compound
Example: Determine the mass percent of each element in H2O.
Determine the mass percent of each element in the following compounds
1.
H2SO4
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4. Ca(OH)2
x
100
1.
Hydrochloric Acid
3. MgCl2
5. Sodium Oxide
6. Nitrogen Trioxide
6.2 Formulas of Compounds
Empirical Formula -
Molecular Formula -
6.3 Calculation of Empirical Formulas
To calculate the empirical formula of a compound, we first determine the relative masses of the various ________________
that are present.
One way to find the empirical formula is to measure the masses of elements that react to form the compound. For example,
suppose we have a 3.450 g sample of nitrogen that reacts with 1.970 g of oxygen. Determine the empirical formula for this
compound.
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Sometimes the relative numbers of moles you get when you calculate an _____________ formula will turn out to be
nonintegers. When this happens, you must convert to the appropriate whole numbers.
Problems
1.
When a 2.000 g sample of iron metal is heated in air, it reacts with oxygen to achieve a final mass of 2.573 g.
Determine the empirical formula for this compound.
2.
A 4.550 g sample of cobalt reacts with 5.475 g of chlorine to form a binary compound. Determine the empirical
formula for this compound.
3.
Phosphoric acid is found in some soft drinks. A sample of phosphoric acid contains 0.3086 g of hydrogen, 3.161 g of
phosphorus, and 6.531 g of oxygen. Determine the empirical formula for phosphoric acid.
4.
The simplest amino acid, glycine, has the following mass percents: 32.00% carbon, 6.714 % Hydrogen, 42.63%
Oxygen, an 18.66% Nitrogen. Determine the empirical formula of glycine.
5.
A compound has been analyzed and found to have the following mass percent composition: 66.75 % copper, 10.84%
phosphorus, and 22.41% oxygen. Determine the empirical formula for this compound.
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6.8 Calculations of Molecular Formulas
If we know the composition of a compound in terms of the masses (or mass percentages) of the elements present, we
can calculate the empirical formula but not the _______________ formula. To obtain the molecular formula we
must know the __________ ___________.
Example: A compound containing carbon, hydrogen, and oxygen is found to be 40.00% carbon, 6.700% hydrogen, and
53.3% oxygen. The molar mass is 120 g/mol. Determine the molecular formula for this compound.
Problems
1.
A compound with the empirical formula CH2O was found to have a molar mass between 89 and 91 g/mol. What
is the molecular formula of the compound.
2.
A compound with the empirical formula CH2 was found to have a molar mass of approximately 84 g. What is the
molecular formula of the compound?
3. A compound consists of 65.45% C, 5.492% H, and 29.06% O on a mass basis and has a molar mass of approximately
110 g/mol. Determine the molecular formula of the compound.
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