1. Chapter 10 Chemical Quantities
10.1 The Mole: A Measurement of Matter
10.2 Mole-Mass and Mole-Volume Relationships
10.3 Percent Composition and Chemical Formulas
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2. How can you calculate the moles of a substance in a given mass
CHEMISTRY & YOU
How can you calculate the moles of a substance in a given mass
or volume?
Guess how many pennies are in the container. In a similar way, chemists use the relationships between the mole and quantities such as mass, volume, and number of particles to solve problems in chemistry.
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3. The Mole-Mass Relationship
How do you convert the mass of a substance to the number of moles of the substance?
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4. The Mole-Mass Relationship
Use the molar mass of an element or compound to convert between the mass of a substance and the moles of the substance.
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5. The Mole-Mass Relationship
Use the molar mass of an element or compound to convert between the mass of a substance and the moles of the substance.
The conversion factors for these calculations are based on the relationship molar mass = 1 mol.
molar mass
1 mol
and
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6. Converting Moles to Mass
Sample Problem 10.5
Converting Moles to Mass
Items made out of aluminum, such as aircraft parts and cookware, are resistant to corrosion because the aluminum reacts with oxygen in the air to form a coating of aluminum oxide (Al2O3). This tough, resistant coating prevents any further corrosion. What is the mass, in grams, of 9.45 mol of aluminum oxide?
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7. Analyze 1 The desired conversion is moles → mass. KNOWN
Sample Problem 10.5
Analyze 1
The desired conversion is moles → mass.
KNOWN
number of moles = 9.45 mol Al2O3 UNKNOWN mass = ? g Al2O3
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8. Calculate Solve for the unknown.
Sample Problem 10.5
Calculate Solve for the unknown. 2
First determine the mass of 1 mol of Al2O3.
2 × 27.0 g Al = 54.0 g Al
3 × 16.0 g O = 48.0 g O
1 mol Al2O3 = 54.0 g Al g O = g Al2O3
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9. Calculate Solve for the unknown.
Sample Problem 10.5
Calculate Solve for the unknown. 2
Identify the conversion factor
Use the relationship 1 mol Al2O3 = g Al2O3.
1 mol Al2O3
102.0 g Al2O3
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10. Calculate Solve for the unknown.
Sample Problem 10.5
Calculate Solve for the unknown. 2
Multiply the given number of moles by the conversion factor.
9.45 mol Al2O3 ×
102.0 g Al2O3
1 mol Al2O3
= 964 g Al2O3
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11. Converting Mass to Moles
Sample Problem 10.6
Converting Mass to Moles
When iron is exposed to air, it corrodes to form a red-brown rust. Rust is iron(III) oxide (Fe2O3). How many moles of iron(III) oxide are contained in 92.2 g of pure Fe2O3?
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12. Analyze List the known and the unknown.
Sample Problem 10.6
Analyze List the known and the unknown. 1
The conversion is mass → moles.
KNOWN mass = 92.2 g Fe2O3 UNKNOWN number of moles = ? mol Fe2O3
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13. Calculate Solve for the unknown.
Sample Problem 10.6
Calculate Solve for the unknown. 2
First determine the mass of 1 mol of Fe2O3.
2 × 55.8 g Fe
= g Fe
3 x16.0 g O
= 48.0 g O
1 mol Fe2O3 = g Fe g O = g Fe2O3
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14. Calculate Solve for the unknown.
Sample Problem 10.6
Calculate Solve for the unknown. 2
Identify the conversion facto.
159.6 g Fe2O3
1 mol Fe2O3
Note that the known unit (g) is in the denominator and the unknown unit (mol) is in the numerator.
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15. Calculate Solve for the unknown.
Sample Problem 10.6
Calculate Solve for the unknown. 2
Multiply the given mass by the conversion factor.
92.2 g Fe2O3 ×
1 mol Fe2O3
159.6 g Fe2O3
= mol Fe2O3
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16. The Mole-Volume Relationship
How do you convert the volume of a gas at STP to the number of moles of the gas?
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17. The Mole-Volume Relationship
Notice that the volumes of one mole of different solid and liquid substances are not the same.
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18. The Mole-Volume Relationship
Avogadro’s Hypothesis
Avogadro’s hypothesis states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.
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19. The Mole-Volume Relationship
Avogadro’s Hypothesis
Whether the particles are large or small, large expanses of space exist between individual particles of gas.
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20. The Mole-Volume Relationship
Avogadro’s Hypothesis
The volume of a gas varies with a change in temperature or a change in pressure.
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21. The Mole-Volume Relationship
Avogadro’s Hypothesis
The volume of a gas varies with a change in temperature or a change in pressure.
Thus, the volume of a gas is usually measured at standard temperature and pressure.
Standard temperature and pressure (STP) means a temperature of 0°C and a pressure of kPa, or 1 atmosphere (atm).
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22. The Mole-Volume Relationship
Avogadro’s Hypothesis
At STP, 1 mol of gas = 22.4 L.
The quantity, 22.4 L, is called the molar volume of a gas.
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23. The Mole-Volume Relationship
Calculating the Volume and Moles of a Gas at STP
The conversion factors for these calculations are based on the relationship 22.4 L = 1 mol at STP.
22.4 L
1 mol
and
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24. Calculating Gas Quantities at STP
Sample Problem 10.7
Calculating Gas Quantities at STP
Sulfur dioxide (SO2) is a gas produced by burning coal. It is an air pollutant and one of the causes of acid rain. Determine the volume, in liters, of 0.60 mol SO2 gas at STP.
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25. Analyze. 1 KNOWNS number of moles = 0.60 mol SO2
Sample Problem 10.7
Analyze. 1
KNOWNS number of moles = 0.60 mol SO2
1 mol SO2 = 22.4 L SO2 at STP UNKNOWN volume = ? L SO2
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26. Calculate Solve for the unknown.
Sample Problem 10.7
Calculate Solve for the unknown. 2
First identify the conversion factor
22.4 L SO2
1 mol SO2
The following relationship applies for gases at STP: 22.4 L = 1 mol.
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27. Calculate Solve for the unknown.
Sample Problem 10.7
Calculate Solve for the unknown. 2
Multiply the given number of moles by the conversion factor.
0.60 mol SO2 ×
22.4 L SO2
1 mol SO2
= 13 L SO2
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28. The Mole-Volume Relationship
Calculating Molar Mass and Density
Different gases have different densities.
Usually the density of a gas is measured in grams per liter (g/L) and at a specific temperature.
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29. Calculating the Molar Mass of a Gas at STP
Sample Problem 10.8
Calculating the Molar Mass of a Gas at STP
The density of a gaseous compound containing carbon and oxygen is found to be g/L at STP. What is the molar mass of the compound?
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30. Sample Problem 10.8
Analyze 1
KNOWNS density = g/L 1 mol of gas at STP = 22.4 L UNKNOWN molar mass = ? g/mol
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31. Calculate Solve for the unknown.
Sample Problem 10.8
Calculate Solve for the unknown. 2
First identify the conversion factor needed to convert density to molar mass.
22.4 L
1 mol
Use the density and molar volume at STP to calculate the molar mass.
molar mass = g
mol = L ×
22.4 L
1 mol
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32. Calculate Solve for the unknown.
Sample Problem 10.8
Calculate Solve for the unknown. 2
Multiply the given density by the conversion factor.
= 44.0 g/mol
1.964 g
1 L
22.4 L
1 mol ×
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33. Why does one mole of any gas occupy the same volume (22
Why does one mole of any gas occupy the same volume (22.4 L) at standard temperature and pressure?
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34. Why does one mole of any gas occupy the same volume (22
Why does one mole of any gas occupy the same volume (22.4 L) at standard temperature and pressure?
Gas molecules do vary in size, just like molecules of solids and liquids, but the particles in a gas are always so far apart that the change in volume of the molecules doesn’t change the volume the gas occupies at STP.
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