Chapter 7 Lecture Basic Chemistry Fourth Edition 7.3 Calculations Using Molar Mass Learning Goal...

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.

© 2014 Pearson Education, Inc.

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

© 2014 Pearson Education, Inc.

Using Molar Mass

© 2014 Pearson Education, Inc.

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?

© 2014 Pearson Education, Inc.

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

© 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 3 Determine the molar mass and write conversion factors.

© 2014 Pearson Education, Inc.

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.

© 2014 Pearson Education, Inc.

Conversion Factors for Compounds

A box of salt contains 737 g of NaCl. How manymoles of NaCl are present in the box?

© 2014 Pearson Education, Inc.

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

© 2014 Pearson Education, Inc.

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

© 2014 Pearson Education, Inc.

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.

© 2014 Pearson Education, Inc.

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

© 2014 Pearson Education, Inc.

Converting Mass to Molecules

© 2014 Pearson Education, Inc.

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?

© 2014 Pearson Education, Inc.

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

© 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 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

© 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 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