Chem Instructions Before class starts, get a piece of paper and title it Ch 11 Notes – The Mole

Chapter 11: The Mole

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 ×

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 × 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 Al6.022 × atoms = 1.20 × 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 × EE 23. When stating the answer don’t forget to include the “× ” mols HCl × molecules = 2.15 × molecules HCl 1 mol

The opposite can also be done. How many moles is 9.03 × atoms of K? 9.03 × atoms K 1 mol = 1.50 mols K × atoms

Notice, in both cases you use that fact that 1 mol = × (this is called a conversion factor). Whether the × 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?

=

2.9 mols Fe =

How would you set up the railroad tracks to find out how many atoms is 2.9 moles of Fe? 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? 2.9 mols Fe × atoms = 1 mol

How would you set up the railroad tracks to find out how many atoms is 2.9 moles of Fe? 2.9 mols Fe × atoms = 1.75 × atoms Fe 1 mol

How would you set up the railroad tracks to find out how many moles is 4.9 × molecules of Rb 3 P? =

4.9 × molecules Rb 3 P =

How would you set up the railroad tracks to find out how many moles is 4.9 × molecules of Rb 3 P? 4.9 × molecules Rb 3 P 1 mol = × molecules

How would you set up the railroad tracks to find out how many moles is 4.9 × molecules of Rb 3 P? 4.9 × molecules Rb 3 P 1 mol = mols Rb 3 P × molecules

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 = grams of sulfur. Likewise, 2 mols of sulfur = 2 × or grams of sulfur, etc. This allows for amounts of elements to be easily measured in the laboratory and turned into moles. 16 S

A student measures out 12 g of Mg in lab. How many moles does this student have? 12 g Mg1 mol = 0.49 mols Mg 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 ÷ Notice the conversion factor is unique for each element and must come from the periodic table. 12 g Mg1 mol = 0.49 mols Mg 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 × mols B10.81 g = g B 1 mol

How would you set up the railroad tracks to find out how many grams is 2.9 moles of Fe? =

2.9 mols Fe =

How would you set up the railroad tracks to find out how many grams is 2.9 moles of Fe? 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? 2.9 mols Fe g = 1 mol

How would you set up the railroad tracks to find out how many grams is 2.9 moles of Fe? 2.9 mols Fe g = g Fe 1 mol

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? =

4.3 g P =

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? 4.3 g P = g

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? 4.3 g P1 mol = g

How would you set up the railroad tracks to find out how many moles is 4.3 grams of P? 4.3 g P1 mol = 0.14 mols P g

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

A student needs 2.6 × 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 ÷ EE 23 × × atoms F 1 mol g = 8.20 g F × 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 ÷ × EE g Al1 mol × atoms = 1.27 × atoms Al g1 mol

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × atoms of Rb? =

9.4 × atoms Rb =

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × atoms of Rb? 9.4 × atoms Rb = × atoms

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × atoms of Rb? 9.4 × atoms Rb 1 mol = × atoms

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × atoms of Rb? 9.4 × atoms Rb 1 mol = × atoms 1 mol

How would you set up railroad tracks to calculate how many grams of Rb are 9.4 × atoms of Rb? 9.4 × atoms Rb 1 mol g = g Rb × atoms 1 mol

how many atoms of Rb are 17.8 grams of Rb? =

17.8 g Rb =

how many atoms of Rb are 17.8 grams of Rb? 17.8 g Rb = g

how many atoms of Rb are 17.8 grams of Rb? 17.8 g Rb1 mol = g

how many atoms of Rb are 17.8 grams of Rb? 17.8 g Rb1 mol = g1 mol

how many atoms of Rb are 17.8 grams of Rb? 17.8 g Rb1 mol × atoms = g1 mol

how many atoms of Rb are 17.8 grams of Rb? 17.8 g Rb1 mol × atoms = 1.25 × atoms Rb g1 mol

11.3: Moles of Compounds

A properly written compound shows the ratio of atoms in the compound. For example, sodium carbonate (Na 2 CO 3 ) 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 Na22.99 g = g Na 1 mol 1 mol C g = g C 1 mol 3 mols O g = g O 1 mol

The total molar mass of Na 2 CO 3 is g g g = g. Once it is known that 1 mol of Na 2 CO 3 = 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 g Na 2 CO 3 or 1 mol g Na 2 CO 3

What is the molar mass for potassium oxide (K 2 O)?

2 mols K = 1 mol O =

What is the molar mass for potassium oxide (K 2 O)? 2 mols K g = 1 mol 1 mol O g = 1 mol

What is the molar mass for potassium oxide (K 2 O)? 2 mols K g = g K 1 mol 1 mol O g = g O 1 mol

What is the molar mass for potassium oxide (K 2 O)? K 2 O = g g = g 2 mols K g = g K 1 mol 1 mol O g = g O 1 mol

If you have 560 grams of K 2 O, how many moles do you have?

560 g K 2 O =

If you have 560 grams of K 2 O, how many moles do you have? 560 g K 2 O1 mol = g

If you have 560 grams of K 2 O, how many moles do you have? 560 g K 2 O1 mol = 5.95 mol K 2 O g

If you have 3.4 moles of K 2 O, how many grams do you have?

3.4 mols K 2 O =

If you have 3.4 moles of K 2 O, how many grams do you have? 3.4 mols K 2 O g = 1 mol

If you have 3.4 moles of K 2 O, how many grams do you have? 3.4 mols K 2 O g = g K 2 O 1 mol