10.2 Mole-Mass and Mole- Volume Relationshipsweb.eccrsd.us/borda/public/honors/HC_CH10_2.pdf · Title: HC CH10 sec 2.ppt Author: Kristin Borda Created Date: 1/8/2014 6:02:36 PM

10.2 Mole-Mass and Mole- Volume Relationships

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Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. .

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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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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molar mass (g) 1 mol

1 mol molar mass (g)

and


•  The conversion factors for these calculations are based on the relationship molar mass = 1 mol.


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Items made out of aluminum are resistant to corrosion because the aluminum reacts with oxygen in the air to form a coating of aluminum oxide.

What is the mass (g) of 9.45 mol of aluminum oxide?

Sample Problem 10.5

Converting Moles to Mass


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KNOWN number of moles = 9.45 mol Al2O3 UNKNOWN mass = ? g Al2O3

Sample Problem 10.5

Analyze List the known and the unknown. 1


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First determine the mass of 1 mol of Al2O3.

Sample Problem 10.5

Calculate Solve for the unknown. 2

2 mol Al × = 54.0 g Al

3 mol O × = 48.0 g O

1 mol Al2O3 = 54.0 g Al + 48.0 g O = 102.0 g Al2O3

27.0 g Al 1 mol Al 16.0 g O 1 mol O


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Sample Problem 10.5


9.45 mol Al2O3 × 102.0 g Al2O3

1 mol Al2O3

= 964 g Al2O3


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•  The number of moles of Al2O3 is approximately 10, and each has a mass of approximately 100 g. So, the answer should be close to 1000 g.

•  Check significant figures.

Sample Problem 10.5

Evaluate Does the result make sense? 3


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When iron is exposed to air, it corrodes to form a red-brown rust known as iron(III) oxide (Fe2O3).

How many moles of iron(III) oxide are contained in 92.2 g of pure Fe2O3?

Converting Mass to Moles

Sample Problem 10.6


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KNOWN mass = 92.2 g Fe2O3 UNKNOWN number of moles = ? mol Fe2O3

Sample Problem 10.6

Analyze List the known and the unknown. 1


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First determine the mass of 1 mol of Fe2O3.

1 mol Fe2O3 = 111.6 g Fe + 48.0 g O = 160. g Fe2O3

2 mol Fe × = 111.6 g Fe 55.8 g Fe 1 mol Fe

3 mol O × = 48.0 g O 16.0 g O 1 mol O

Sample Problem 10.6



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92.2 g Fe2O3 × 1 mol Fe2O3

160. g Fe2O3

= 0.578 mol Fe2O3

Sample Problem 10.6



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Does the result make sense?

Sample Problem 10.6

Evaluate 3


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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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Notice that the volumes of one mole of different solid and liquid substances are not the same.



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However, the volumes of moles of gases, measured under the same physical conditions, are very predictable.



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Equal volumes of gases at the same temperature and pressure contain equal numbers of particles.


Avogadro’s Hypothesis


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The volume of a gas varies with a change in temperature or a change in pressure.



•  The volume of a gas is usually measured at STP.

•  0°C

•  101.3 kPa, or 1 atmosphere (atm).


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At STP, 1 mol, or 6.02 × 1023 representative particles, of any gas occupies a volume of 22.4 L.

•  The quantity, 22.4 L, is called the molar volume of a gas.




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The size of the individual particles of the gas do not alter the volume, because there is so much space between the particles.




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The molar volume is used to convert between the number of moles of gas and the volume of the gas at STP.

Calculating the Volume and Moles of a Gas at STP

22.4 L 1 mol

1 mol 22.4 L

and



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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.

Sample Problem 10.7

Calculating Gas Quantities at STP


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KNOWNS number of moles = 0.60 mol SO2 1 mol SO2 = 22.4 L SO2 at STP UNKNOWN volume = ? L SO2

Sample Problem 10.7

Analyze List the knowns and the unknown. 1


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First identify the conversion factor relating moles of SO2 to volume of SO2 at STP.

22.4 L SO2 1 mol SO2

Sample Problem 10.7



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Multiply the given number of moles by the conversion factor.

Sample Problem 10.7


0.60 mol SO2 × 22.4 L SO2 1 mol SO2

= 13 L SO2


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•  Estimate and check your work.

•  Check significant figures.

Sample Problem 10.7

Evaluate Does the result make sense? 3


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The density of a gaseous compound containing carbon and oxygen is found to be 1.964 g/L at STP. What is the molar mass of the compound?

Sample Problem 10.8

Calculating the Molar Mass of a Gas at STP


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The molar mass of the compound is calculated from the known density of the compound and the molar volume at STP.

KNOWNS density = 1.964 g/L 1 mol of gas at STP = 22.4 L UNKNOWN molar mass = ? g/mol

Sample Problem 10.8

Analyze List the knowns and the unknown. 1


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Sample Problem 10.8

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 = g L ×

22.4 L 1 mol



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Multiply the given density by the conversion factor.

Sample Problem 10.8


= 44.0 g/mol

1.964 g 1 L

22.4 L 1 mol ×


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The mole is at the center of your chemical calculations.


•  To convert from one unit to another, you must use the mole as an intermediate step.

Documents

10.2 Mole-Mass and Mole- Volume Relationshipsweb.eccrsd.us/borda/public/honors/HC_CH10_2.pdf · Title: HC CH10 sec 2.ppt Author: Kristin Borda Created Date: 1/8/2014 6:02:36 PM