Bell Ringer 3-31-14

4Al + 3O2 → 2Al2O3

• For every ____ atoms of Al that react, there are ____ formula units of Al2O3 produced.

• Determine which numbers go in the blanks, then write the statement above as a ratio

4Al + 3O2 → 2Al2O3

For every 4 atoms of Al that react, there are 2 formula units of Al2O3 produced.

Write the statement above as a ratio 4 atoms Al__

2 form u. Al2O3

Ratios in Chemical Equations

3-31-14

In a balanced chemical equation:

The coefficients tell you the relative amounts of each reactant and product

Use the coefficients as the numbers in your ratio

So far, we have learned that units may be atoms, molecules, or formula units

• Atoms – elements (not diatomic, ex. Al, C)

• Molecules – diatomic elements and covalent compounds (made of nonmetals, ex. O2, H2O)

• Formula Units - ionic compounds (made of metals + nonmetals, ex. NaCl, LiO2)

Visualizing at the Atomic Level

4Al + 3O2 → 2Al2O3

Looks like this: + →

Can we actually count atoms?

• No! We cannot see individual atoms, molecules, or formula units

So scientists came up with a new unit (a mole) that is sooooooooooo big that you can see a mole of atoms (or molecules, or formula units)

The Mole

An amount of particles of a pure substance.

It is a very, very, very, very, very, very, very, very LARGE number

MOLE = 6.02 x 10 23

Review: Scientific Notation6.02 x 10 23 = 602,000,000,000,000,000,000,000

Other Scientific Notation Problems:4.267 x 10 8 =426,700,000 =4.267 x 10 -8 =

426,700,000

4.267 x 10 8

.00000004267

Mole is a word that is used to indicate a number. What are some other words we use to tell how

many of something we have?1. PAIR=

2. DOZEN =

3. GROSS =

2

12

144

What is a mole?602,000,000,000,000,000,000,000 =

six hundred and two sextillion =

6.02 x 1023

Why use a mole?

• Scientists use the mole, and the concept of molar mass to determine how much of each reactant to use, and to predict how much of each product they will get.

• Molar mass is the mass of one mole of a substance (more about that later this week)

Just how big is a mole?

• 6.02 X 1023 Watermelon Seeds: Would be found inside a melon slightly larger than the moon.

• 6.02 X 1023 Donut Holes: Would cover the earth and be 5 miles (8 km) deep.

• 6.02 X 1023 Pennies: Would make at least 7 stacks that would reach the moon.

• 6.02 X 1023 Grains of Sand: Would be more than all of the sand on Chicago’s Beaches.

How many atoms are in a mole of hydrogen atoms?

6.02 x 10 23

How many molecules are in a mole of water molecules?

6.02 x 10 23

How many marshmallows are in a mole of marshmallows?

6.02 x 10 23

EXAMPLE: Using moles in a ratio:

C3H8 + 5O2 → 3CO2 + 4H2O

For every __ _ mole of C3H8 reacted, there are ____ moles of CO2 produced.

There are __ moles of H2O produced for every _____ moles of O2 that react.

Write the ratios:

1 mole C3H8 4 moles H2O 3 moles CO2 5 moles O2

1 3

4 5

1

What is a mole?602,000,000,000,000,000,000,000 =

six hundred and two sextillion =

6.02 x 1023

More Practice:2HgO → 2Hg + O2

What is the ratio of moles of HgO to moles of Hg?

2 moles HgO or 1 mole HgO2 moles Hg 1 mole Hg

So if you react 7 moles of HgO, how many moles of Hg are produced?

What is the mass of one mole of: look at your periodic table, Write our answer in your notes, then raise your hand

C S

Cu Fe

Hg

3.2

If you wanted to find the mass of the whole class, what would you have to do?

• Find the mass of each student (put them on a scale)

• Add the mass of each student together• = total mass

If you wanted to find the mass a whole compound, what would you have to do?

• Find the mass of each atom (look at the periodic table)

• Add the mass of each atom together• = total mass

Molar mass (or molecular weight) is the total amount ofthe atomic masses in a molecule. Unit = u

S-1 32.07 amuO-2 + 2 x 15.99 amu SO2 64.05 amu

For any molecule molecular mass (u) = molar mass (grams)

1 molecule SO2 = 64.05 amu

1 mole SO2 = 64.05 g SO2 3.3

Steps:1. Determine how many atoms are there of each element?2. What are the masses? 3. Add all the masses

SO2

Example 1: show your work

Find the Molecular Mass of H2O

H - 2O- 1

X 1.008 = 2.016X 15.99 = 15.99+

18.006 g

Example 1: show your work

Find the Molecular Mass of 2 moles of H2O

H - 2O- 1

X 1.008 = 2.016X 15.99 = 15.99+

18.006 g1 mol of H2O18.006 g of H2O

2 mol of H2O

2 mol of H2O

1 mol of H2O

18.006 g of H2O =

= 36.0121 =

36.012 g of H2O

Example 3: show your work

Find the Molecular Mass of CaCl2

Ca - 1Cl - 2

X 40.08 = 40.08X 35.45 = 70.9+

110.98 g

Example 4: show your work

Find the Molecular Mass of 4 moles of CaCl2

1 mol of CaCl2

110.98 g of CaCl2

4 mol of CaCl2

4 mol of CaCl2

1 mol of CaCl2

110.98 g of CaCl2 =

= 443.921 =

443.92 g of CaCl2

Honors Exit Slip: Half sheet, 6 Formative Assessment points (Grade category 15%)

1. How many atoms are there in a mole of helium?

2. How many molecules are there in a mole of methane?

3. What is the mass of 1 mole of magnesium?

4. What is the mass of 1 mole of carbon dioxide? What is the mass of 2 moles of Carbon Dioxide?

5. What is the mass of one mole of O2? What is the mass of 2 moles of O2?

6. What is the mass of one mole of LiCN? What is the mass of 5 moles of LiCN?

Exit Slip: Half sheet, 6 Formative Assessment points (Grade category 15%)

1. How many atoms are there in a mole of helium?

2. How many molecules are there in a mole of methane?

3. What is the mass of 1 mole of magnesium?

4. What is the mass of 1 mole of carbon dioxide?

5. What is the mass of one mole of O2?

6. What is the mass of one mole of LiCN?