Dimensional Analysis1. Determine what your final unit needs to be

- "what do you want"

2. Determine what unit you've been given- "what do you have"

3. Set up a ratio so your units cancel- usually: want on top / have on bottom

EX: How many minutes are in a day? How many seconds?

Moles

• Called the “chemist’s dozen”

• A really big quantity to measure really tiny things.

• 6.02 x 10 23 particles per mole

• Can measure atoms, molecules, formula units, ions, electrons, etc.

• Allows us to convert from particles to mass (grams) or grams to particles

A mole of ……

• Marbles would cover the earth to a depth of 6 km.

• Glasses of water would fill the earth’s oceans.

• Sand grains would fill all the beaches in the world.

• Paper clips would stretch to the nearest galaxy 2 million light years away.

Try It

1. Determine the number of atoms in 2.50 mol Zn.

2. Given 3.25 mol AgNO3, determine the number of formulas units.

3. Calculate the number of molecules in 11.5 mol H2O

Answers

1. 2.50 mol Zn x 6.02 x 1023 atoms/mol = 1.51 x 1024 atoms Zn

2. 3.25 mol AgNO3 x 6.02 x 1023 formula units/mol = 1.96 x 1024 formula units AgNO3

3. 11.5 mol H20 x 6.02 x 1023 molecules/mol = 6.92 x 1024 molecules H20

Try It• How many moles are each of the following?

1. 5.75 x 1024 atoms Al

2. 3.58 x 1023 formulas units ZnCl2

Answers

1. 5.75 x 1024 atoms Al x 1 mole/6.02 x 1023 atoms = 9.55 mol Al

2. 3.58 x 1023 formulas units ZnCl2 x 1 mole/6.02 x 1023 formula units = .595 mol ZnCl2

Mass & the Mole

• Which would weigh more a mole of helium or a mole of lead? WHY?

• Atomic mass = amu / atom

• Molar mass = grams / mole

• Chromium has an atomic mass of 52.00 amu so its molar mass = 52.00 grams

• How much would 2 moles of Cr weigh?

• How much would .0450 moles weigh?

Try It

• Determine the mass in grams of each of the following:

3.57 mol Al 42.6 mol Si

• Determine the number of moles in each of the following:

25.5 g Ag 300.0 g S

Answers

1. 3.57 mol Al x 26.982 g/mol = 96.3 g Al

2. 42.6 mol Si x 28.086 g/mol = 1200 g Si

3. 25.5 g Ag x 1 mol/107.868 g = .236 mol Ag

4. 300.0 g S x 1 mol/32.065 g = 9.356 mol S

Ratios to Know

1 mole = 6.02 x 1023 particles / atoms / etc

1 mole = X grams (determine X using the periodic table)