chapter 7 lecture basic chemistry fourth edition 7.3 calculations using molar mass learning goal...
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Chapter 7 Lecture
Basic ChemistryFourth Edition
7.3 Calculations Using Molar Mass
Learning Goal Given the number of moles of a substance, calculate the mass in grams; given the mass, calculate the number of moles.
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Chapter 7 Chemical Quantities
The molar mass
• is a useful conversion factor
• converts moles of a substance to grams
• converts mass in grams of a substance to moles
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Using Molar Mass
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Guide to Calculating Moles from Grams or Grams from Moles
Silver metal is used in the manufacture oftableware, mirrors, dental alloys, and jewelry. If the design for a piece of jewelry requires0.750 mole of silver, how many grams of silverare needed?
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Learning Check
If the design for a piece of jewelry requires0.750 mole of silver, how many grams of silverare needed?
Step 1 State the given and needed quantities.Given: 0.750 mole of AgNeed: grams of Ag
© 2014 Pearson Education, Inc.
Solution
If the design for a piece of jewelry requires0.750 mole of silver, how many grams of silverare needed?
Step 2 Write a plan to convert moles to grams.
0.750 mol of Ag grams of AgMolar MassMolar Mass
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Solution
If the design for a piece of jewelry requires0.750 mole of silver, how many grams of silverare needed?
Step 3 Determine the molar mass and write conversion factors.
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Solution
© 2014 Pearson Education, Inc.
Solution
If the design for a piece of jewelry requires0.750 mole of silver, how many grams of silverare needed?
Step 4 Set up the problem to convert moles to grams (or grams to moles).
Conversion factors are written for compounds inthe same way as those written for elements.
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Conversion Factors for Compounds
A box of salt contains 737 g of NaCl. How manymoles of NaCl are present in the box?
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Learning Check
A box of salt contains 737 g of NaCl. How manymoles of NaCl are present in the box?
Step 1 State the given and needed quantities. Given: 737 g NaCl Need: moles of NaCl
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Solution
A box of salt contains 737 g of NaCl. How manymoles of NaCl are present in the box?
Step 2 Write a plan to convert grams to moles.
grams of NaCl moles of NaClMolar MassMolar Mass
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Solution
© 2014 Pearson Education, Inc.
Solution
A box of salt contains 737 g of NaCl. How many moles of NaCl are present in the box?
Step 3 Determine the molar mass and write conversion factors.
(1 × 22.99) + 1(35.45) = 58.44 g/mol
A box of salt contains 737 g of NaCl. How manymoles of NaCl are present in the box?
Step 4 Set up the problem to convert grams to moles.
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Solution
© 2014 Pearson Education, Inc.
Summary of Conversions
Grams ofelement or compound
Moles ofelement or compound
Atoms of element or molecules of compound
Molar Massg/mol
Avogadro’sNumber
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Converting Mass to Molecules
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Guide to Calculating Particles from Mass
A 10.00-lb bag of table sugar contains 4536 g ofsucrose, C12H22O11. How many molecules of
sucrose are present?
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Learning Check
A 10.00-lb bag of table sugar contains 4536 g ofsucrose, C12H22O11. How many molecules of
sucrose are present?Step 1 State the given and needed
quantities.Given: 4536 g sucrose, C12H22O11
Need: molecules of sucrose
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Solution
A 10.00-lb bag of table sugar contains 4536 g ofsucrose, C12H22O11. How many molecules of
sucrose are present?Step 2 Write a plan to convert grams to
particles.
grams of sucrose
moles of sucrose
molecules of
sucroseMolar MassMolar Mass Avogadro’s
NumberAvogadro’s
Number
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Solution
A 10.00-lb bag of table sugar contains 4536 g ofsucrose, C12H22O11. How many molecules of
sucrose are present?Step 3 Write the equalities and conversion
factors.
© 2014 Pearson Education, Inc.
Solution
A 10.00-lb bag of table sugar contains 4536 g ofsucrose, C12H22O11. How many molecules of
sucrose are present?Step 4 Set up the problem to convert grams
to particles.
© 2014 Pearson Education, Inc.
Solution