Friday, March 21st: “A” DayMonday, March 24th: “B” Day

AgendaHomework Questions/CollectFinish section 7.1…finally!In-class:

Practice pg. 231: #1-4Practice pg. 232: #1-3

Homework: Practice worksheet pg 24/25Must SHOW WORK for credit!

Homework“Grams/Moles Calculations”

worksheet

Questions/Problems?

Hand in

Changing Particles Mass

Now that you know how to change particles into moles and moles into mass (in grams), we can put these two steps together to convert from

Particles Mass!

Changing Particles MassYou need 2 steps to change number of particles to

mass, in grams:

1. Change particles to moles using Avogadro’s number

2. Change moles to mass using the molar massTwo different conversion factors must be used!

Particles Mass Sample Problem C, pg. 231

Find the mass in grams of 2.44 X 1024 atoms of carbon, whose molar mass is 12.01 g/mol.

1.Start with what you know: 2.44 X 1024 atoms C2.Use Avogadro’s number as a conversion factor to

change atoms C moles C:2.44 X 1024 atoms C X 1 mol C

6.022 X 1023 atoms C

= 4.05 mol C

Particles Mass Sample Problem C, pg. 231, cont.

3. Now, use molar mass of carbon to change moles C mass (in grams) of C:

4.05 moles C X 12.01 g C 1 mole C

48.6 g C(3 sig figs)

Particles Mass Practice #1

Find the mass in grams of 6.12 X 1014 formula units of rhenium dioxide, ReO2, 218.21 g/mol.

1.Start with what you know: 6.12 X 1014 form. units ReO2

2.Use Avogadro’s number as a conversion factor to change form. units ReO2 moles ReO2:

6.12 X 1014 form. units X 1 mol ReO2

6.022 X 1023 form. units

= 1.02 X 10-9 mole ReO2

Particles Mass Practice #1, cont.

3. Now, use molar mass of ReO2 to change

moles ReO2 mass (in grams) of ReO2:

1.02 X 10-9 mole ReO2 X 218.21 g ReO2

1 mole ReO2

2.23 X 10-7 g ReO2

(3 sig figs)

Changing Mass ParticlesConverting from mass to number of particles is

simply the opposite of what you’ve just done.You need 2 steps to change number of particles to

mass:1. Change mass to moles using molar mass2. Second, change moles to particles using

Avogadro’s number Two different conversion factors must be used!

Mass Particles Sample Problem D, pg. 232

Find the number of molecules present in 47.5 g of glycerol, C3H8O3. The molar mass of glycerol is 92.11 g/mol.

1.Start with what you know: 47.5 g C3H8O3

2. Use molar mass of C3H8O3 to change

mass C3H8O3 moles C3H8O3:

47.5 g C3H8O3 X 1 mol C3H8O3 = .516 mol C3H8O3

92.11 g C3H8O3

Mass Particles Sample Problem D, cont.

3.Now, use Avogadro’s number to change moles molecules:

0.516 mol C3H8O3 X 6.022 X 1023 molecules C3H8O3

1 mole C3H8O3

3.11 X 1023 molecules C3H8O3 (3 sig figs)

Mass Particles Additional Practice

Determine the number of atoms present in 54.3 grams of cobalt, Co.

1. Start with what you know: 54.3 g Co2.Use molar mass of Co to change

mass Co mole Co:

54.3 g Co X 1 mol Co = .921 mole Co58.93 g Co

Mass Particles Additional Practice, cont.

3.Now, use Avogadro’s number to change moles Co atoms Co:

0.921 moles Co X 6.022 X 1023 atoms Co 1 mole Co

5.55 X 1023 atoms Co

In-Class Assignments/HomeworkYou Must SHOW WORK!

Practice pg. 231: #1-4Practice pg. 232: #1-3Practice worksheet, pg. 24/25Concept Review:

“Avogadro’s Number & Molar Conversions”