chapter 11: the mole 11.1 measuring matter roses and eggs are conveniently packaged as a dozen....

Chapter 11: The Mole

11.1 Measuring Matter

11.1 Measuring Matter

Roses and eggs are conveniently packaged as a dozen. Sheets of paper are packaged as a ream.

Small item are packaged in large amounts to make life easier. The same is true for atoms. However, because atoms are really, really, really small, the amounts of them that are packaged together are really, really, really big

A package of atoms or compounds that chemists use is called the Mole (from the Greek word for “pile”).

A package of atoms or compounds that chemists use is called the Mole (from the Greek word for “pile”). A mole (abbreviated “mol”) contains

602,200,000,000,000,000,000,000 of anything. This really large number is often called Avogadro’s Number and is abbreviated 6.022 × 1023.

If you know the number of moles, then the amount of atoms or molecules can be calculated.

How many atoms are in 2 moles of Al?

In a calculator, you would put in 2 × 6.022 EE 23. Pushing the button that says EE takes the place of the “ × 10 ” and is the way calculators are meant to be used.

2 mols Al 6.022 × 1023 atoms= 1.20 × 1024 atoms Al

1 mol

How many molecules of HCl are in 3.57 moles of HCl?

In a calculator, you would put in 3.57 × 6.022 EE 23. When stating the answer don’t forget to include the “× 1024”.

3.57 mols HCl 6.022 × 1023 molecules

= 2.15 × 1024 molecules HCl

1 mol

The opposite can also be done.

How many moles is 9.03 × 1023 atoms of K?

9.03 × 1023 atoms K 1 mol

= 1.50 mols K 6.022 × 1023 atoms

Notice, in both cases you use that fact that 1 mol = 6.022 × 1023 (this is called a conversion factor). Whether the 6.022 × 1023 is on the top or bottom of the railroad tracks depends on what you start the problem with.

How would you set up the railroad tracks to find out how many atoms is 2.9 moles of Fe? You do not need to calculate an answer.

How would you set up the railroad tracks to find out how many atoms is 2.9 moles of Fe? You do not need to calculate an answer.

=

How would you set up the railroad tracks to find out how many atoms is 2.9 moles of Fe? You do not need to calculate an answer.

2.9 mols Fe=

How would you set up the railroad tracks to find out how many atoms is 2.9 moles of Fe? You do not need to calculate an answer.

2.9 mols Fe=

1 mol

How would you set up the railroad tracks to find out how many atoms is 2.9 moles of Fe? You do not need to calculate an answer.

2.9 mols Fe 6.022 × 1023 atoms

= 1 mol

How would you set up the railroad tracks to find out how many atoms is 2.9 moles of Fe? You do not need to calculate an answer.

2.9 mols Fe 6.022 × 1023 atoms = 1.75 × 1024

atoms Fe1 mol

How would you set up the railroad tracks to find out how many moles is 4.9 × 1023 molecules of Rb3P? You do not need to calculate an answer.

=

How would you set up the railroad tracks to find out how many moles is 4.9 × 1023 molecules of Rb3P? You do not need to calculate an answer.

4.9 × 1023 molecules Rb3P

=

How would you set up the railroad tracks to find out how many moles is 4.9 × 1023 molecules of Rb3P? You do not need to calculate an answer.

4.9 × 1023 molecules Rb3P

1 mol=

6.022 × 1023 molecules

How would you set up the railroad tracks to find out how many moles is 4.9 × 1023 molecules of Rb3P? You do not need to calculate an answer.

4.9 × 1023 molecules Rb3P

1 mol= 0.814 mols Rb3P

6.022 × 1023 molecules

11.2 Masses and the Mole

11.2 Masses and the Mole

The mole is not only handy to counting a large amount of atoms or molecules, it is even more

useful when measuring out amounts of elements or compounds. The masses on the periodic table have been designed to be the amount of grams in a mole of that element.

For example, look at sulfur.

The information shown for sulfur tells us that 1 mol of sulfur = 32.066 grams of sulfur. Likewise, 2 mols of sulfur = 2 × 32.066 or 64.132 grams of sulfur, etc. This allows for amounts of elements to be easily measured in the laboratory and turned into moles.

16S

32.066

A student measures out 12 g of Mg in lab. How many moles does this student have?

12 g Mg 1 mol = 0.494 mols Mg

24.31 g

A student measures out 12 g of Mg in lab. How many moles does this student have?

In the calculator you would put in 12 ÷ 24.31. Notice the conversion factor is unique for each element and must come from the periodic table.

12 g Mg 1 mol = 0.494 mols Mg

24.31 g

The opposite can also be done.

A student needs 2.3 mols of B for an experiment. How many grams should this student measure out?

In the calculator you would put in 2.3 × 10.8.

2.3 mols B 10.8 g = 24.8 g B

1 mol

How would you set up the railroad tracks to find out how many grams is 2.9 moles of Fe? You do not need to calculate an answer.

=

How would you set up the railroad tracks to find out how many grams is 2.9 moles of Fe? You do not need to calculate an answer.

2.9 mols Fe=

How would you set up the railroad tracks to find out how many grams is 2.9 moles of Fe? You do not need to calculate an answer.

2.9 mols Fe=

1 mol

How would you set up the railroad tracks to find out how many grams is 2.9 moles of Fe? You do not need to calculate an answer.

2.9 mols Fe 55.8 g=

1 mol

How would you set up the railroad tracks to find out how many grams is 2.9 moles of Fe? You do not need to calculate an answer.

2.9 mols Fe 55.8 g= 162 g Fe

1 mol

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? You do not need to calculate an answer.

=

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? You do not need to calculate an answer.

4.3 g P=

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? You do not need to calculate an answer.

4.3 g P=

31 g

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? You do not need to calculate an answer.

4.3 g P 1 mol=

31 g

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? You do not need to calculate an answer.

4.3 g P 1 mol= 0.139 mols P

31 g

Sections 11.1 and 11.2 can be put together into one big calculation.

A student needs 2.6 × 1023 atoms of fluorine for an experiment. How many grams of fluorine should the student measure out?

In the calculator you would put in 2.6 EE 23 ÷ 6.022 EE 23 × 19.

2.6 × 1023 atoms F

1 mol 19 g = 8.21 g F

6.022 × 1023

atoms 1 mol

Moles will always be in the middle of these kinds of calculations!

The opposite can also be done.

A student has 56.7 grams of aluminum. How many atoms of aluminum does the student have?

In the calculator you would put in 56.7 ÷ 27.0 × 6.022 EE 23.

56.7 g Al 1 mol6.022 × 1023

atoms = 1.26 × 1024 atoms Al

27.0 g 1 mol

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × 1023 atoms of Rb? You do not need to calculate and answer.

=

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × 1023 atoms of Rb? You do not need to calculate and answer.

9.4 × 1023 atoms Rb

=

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × 1023 atoms of Rb? You do not need to calculate and answer.

9.4 × 1023 atoms Rb

= 6.022 × 1023

atoms

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × 1023 atoms of Rb? You do not need to calculate and answer.

9.4 × 1023 atoms Rb 1 mol

= 6.022 × 1023

atoms

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × 1023 atoms of Rb? You do not need to calculate and answer.

9.4 × 1023 atoms Rb 1 mol

= 6.022 × 1023

atoms 1 mol

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × 1023 atoms of Rb? You do not need to calculate and answer.

9.4 × 1023 atoms Rb 1 mol 85.5 g

= 133 g Rb6.022 × 1023

atoms 1 mol

How would you set up railroad tracks to calculate how many atoms of Rb are 17.8 grams of Rb? You do not need to calculate and answer.

=

How would you set up railroad tracks to calculate how many atoms of Rb are 17.8 grams of Rb? You do not need to calculate and answer.

17.8 g Rb

=

How would you set up railroad tracks to calculate how many atoms of Rb are 17.8 grams of Rb? You do not need to calculate and answer.

17.8 g Rb

=

85.5 g

How would you set up railroad tracks to calculate how many atoms of Rb are 17.8 grams of Rb? You do not need to calculate and answer.

17.8 g Rb 1 mol

=

85.5 g

How would you set up railroad tracks to calculate how many atoms of Rb are 17.8 grams of Rb? You do not need to calculate and answer.

17.8 g Rb 1 mol

=

85.5 g 1 mol

How would you set up railroad tracks to calculate how many atoms of Rb are 17.8 grams of Rb? You do not need to calculate and answer.

17.8 g Rb 1 mol6.022 × 1023

atoms=

85.5 g 1 mol

How would you set up railroad tracks to calculate how many atoms of Rb are 17.8 grams of Rb? You do not need to calculate and answer.

17.8 g Rb 1 mol6.022 × 1023

atoms = 1.25 × 1023 atoms Rb

85.5 g 1 mol

11.3: Moles of Compounds

A properly written compound shows the ratio of atoms in the compound. For example, sodium carbonate (Na2CO3) shows that for every 1

compound there are 2 atoms of Na, 1 atom of C, and 3 atoms of O.

This also works with the mole.

This also works with the mole. For 1 mole of the compound, there are 2 moles of Na, 1 mole of C, and 3 moles of O. This information allows us to

calculate the molar mass of the entire compound, often called the formula mass or molecular mass.

2 mols Na 23 g = 46 g Na

1 mol

1 mol C 12 g = 12 g C

1 mol

3 mols O 16 g= 48 g O

1 mol

The total molar mass of Na2CO3 is 46 g + 12 g + 48 g = 106 g.

Once it is known that 1 mol of Na2CO3 = 106 g,

conversion factors can be made of this information:

These conversion factors can then be used in calculations just like in sections 11.1 and 11.2.

106 g Na2CO3or

1 mol

1 mol 106 g Na2CO3

What is the molar mass for potassium oxide (K2O)?

What is the molar mass for potassium oxide (K2O)?

2 mols K =

1 mol O =

What is the molar mass for potassium oxide (K2O)?

2 mols K 39 g =

1 mol

1 mol O 16 g =

1 mol

What is the molar mass for potassium oxide (K2O)?

2 mols K 39 g = 78 g K

1 mol

1 mol O 16 g = 16 g O

1 mol

What is the molar mass for potassium oxide (K2O)?

K2O = 78 g + 16 g = 94g

2 mols K 39 g = 78 g K

1 mol

1 mol O 16 g = 16 g O

1 mol

If you have 560 grams of K2O, how many moles do you have?

If you have 560 grams of K2O, how many moles do you have?

560 g K2O =

If you have 560 grams of K2O, how many moles do you have?

560 g K2O 1 mol =

94 g

If you have 560 grams of K2O, how many moles do you have?

560 g K2O 1 mol = 5.96 mol K2O

94 g

If you have 3.4 moles of K2O, how many grams do you have?

If you have 3.4 moles of K2O, how many grams do you have?

3.4 mols K2O =

If you have 3.4 moles of K2O, how many grams do you have?

3.4 mols K2O 94 g =

1 mol

If you have 3.4 moles of K2O, how many grams do you have?

3.4 mols K2O 94 g = 320 g K2O

1 mol