Launch: 12/2   Grab your binder and immediately take a seat!

  Place homework (practice questions), binder paper, and a pen/pencil on your desk.

Today’s Objective: I can convert between grams and atoms using both molecular mass and Avogadro’s number as a conversion factors

Tonight’s HW: Finish the back of the practice question worksheet

Launch 12/2 4.  How many molecules of C3OH are in .5 moles?

a.  3.01 X 1023 molecules b.  6.02 X 1023 molecules

c.  9.03 X 1023 molecules d.  1.204 X 1024 atoms

Launch 12/2 5.  If there are 1.204 X 1024 particles of gold (Au), how

many moles are there? a.  .5 moles b.  1 mole c.  2 moles

d.  4 moles

Announcements   Quiz on Friday

  The mole   Conversions

  Unit exam in 2 weeks

How many atoms? – Part II Mr. Heffner 12/1/09

How many atoms?   Conversion factors…

  are used to convert one unit to another unit

? grams 1 mole

..or particles, or molecules

Molar Mass Avogadro’s #

? grams/mole 6.02 X 1023 atoms/mole

Grams Moles Atoms Moles

6.02 X 1023 atoms 1 mole

1 mole ? grams

1 mole 6.02 X 1023 atoms

sum of atomic masses

How many atoms?   What if we want to convert grams atoms?

  Need to use both conversion factors!

How many atoms?   There is a 3-step process for conversions:

1.  Write down the starting unit and look at the ending unit. 2.  Write the conversion factor with the starting units on the

bottom.   If grams, start with molar mass

  If atoms (or particles, or molecules), start with Avogadro’s #

3.  Cancel like terms and multiply across the top and bottom.

Example #1 How many atoms are there in 12.01 grams of carbon (C)?

  Step #1: Write down the starting unit and look at the ending unit.

12.01 grams

How many atoms are there in 12.01 grams of carbon (C)?

  Step #2: Write the conversion factor with the starting units on the bottom.

1 mol 12.01 g

Example #1

12.01 g X =6.02 X 1023 atoms 1 mol

X

Start with molecular

mass

Then use Avogadro’s #

How many atoms are there in 12.01 grams of carbon (C)?

  Step #3: Cancel like terms and multiply across the top and bottom

1 mol 12.01 g

Example #1

12.01 g X =6.02 X 1023 atoms 1 mol

X

=1 X 6.02 X 1023 atoms 1

=6.02 X 1023 atoms

Ignore

Example #3 How many grams of CH4 are there in 12.04 X 1023 molecules?

Step #1: Write down the starting unit and look at the ending unit.

12.04 X 1023 molecules

How many grams of CH4 are there in 12.04 X 1023 molecules?

  Step #2: Write the conversion factor with the starting units on the bottom.

16.05 g 1 mol

Example #3

12.04 X 1023 molecules X =1 mol 6.02 X 1023 molecules

X

Start with Avogadro’s #

Then use molecular

mass

How many grams of CH4 are there in 12.04 X 1023 molecules?

  Step #3: Cancel like terms and multiply across the top and bottom

16.05 g 1 mol

Example #3

12.04 X 1023 molecules X =1 mol 6.02 X 1023 molecules

X

=12.04 X 1 X 16.05 g 6.02 X 1

=32.10 g 2 X 16.05 g =

Example #2 How many atoms are there in 16.00 grams of O2?

  Step #1: Write down the starting unit and look at the ending unit.

16.00 grams

How many atoms are there in 16.00 grams of O2?

  Step #2: Write the conversion factor with the starting units on the bottom.

1 mol 32.00 g

Example #2

16.00 g X =6.02 X 1023 atoms 1 mol

X

Start with molecular

mass

Then use Avogadro’s #

How many atoms are there in 16.00 grams of O2?

  Step #3: Cancel like terms and multiply across the top and bottom

1 mol 32.00 g

Example #2

16.00g X =6.02 X 1023 atoms 1 mol

X

=16.00 X 6.02 X 1023 atoms 32.00 X 1

=3.01 X 1023 atoms

Ignore

.5 X 6.02 X 1023 atoms =

Whiteboards   Work in pairs

  Trade-off marker every question

  You have 60 seconds to solve the question   Show all of your work!   Don’t forget units!

  Lift board only when prompted

How many atoms are there in 8.00 grams of helium (He) ?

How many molecules are there in 4.04 grams of H2?

What is the mass (in grams) of 6.02 X 1023 particles

of gold (Au)?

How many grams does 3.01 X 1023 molecules

of HCl weight?

Practice Questions   Practice question worksheet

Exit Slip 1.  Which conversion factor would need to be used to

convert between gramsmoles? a.  Avogadro’s number b.  6.02 X 1023 atoms/mole c.  Molecular mass

d.  Atomic weight

Exit Slip 2.  Which conversion factor would need to be used to

convert grams into atoms? a.  Avogadro’s number b.  Atomic weight c.  Molecular mass

d.  both a & c

Exit Slip 3.  Which of the following correctly shows how to convert

64.00g of O2 to atoms?

a.  32.00g X

b.  64.00g X

c.  64.00g X X

d.  64.00 g X X

6.02 X 1023 atoms 32.00g

1 mole 32.00 g

6.02 X 1023 atoms 1 mole

1 mole 32.00 g

1 atoms 32.00 moles

1 mole 6.02 X 1023 g

Exit Slip 4.  How many atoms of nitrogen (N) are there in 14.01g?

a.  3.01 X 1023 atoms b.  6.02 X 1023 atoms

c.  9.03 X 1023 atoms d.  1.204 X 1024 atoms

Exit Slip 5.  How many grams does 12.04 X 1023 molecules of

H2O weigh? a.  9.01g b.  18.02g c.  27.03g

d.  36.04g

Homework   Finish practice questions

  Study for Friday’s Quiz!