The Mole ConceptIntroduction

Number of Particles and MolesTopic 1.2

Dimensional Analysis

• starting with one unit of measurement and ending up with a different one

• “cancel out” what you don’t want• use conversion factors (fraction that equals one)

• the numerator will contain the unit you want• the denominator will contain the unit you are trying

to get rid of

• try to predict a “ball park answer” if possible so you might recognize a wrong answer

• sometimes they can be done in one step

• example: 23,532 seconds = ? minutes

23,532 sec. X 1 min. 1 60 sec. 392.20 min.

• sometimes they take multiple steps

• example: 23,532 seconds = ? hours

23,532 sec. X 1 min. X 1 hour = 1 60 sec. 60 min.

6.5367 hours

• but if you don’t know the conversion factor(s), the problem becomes impossible

• example: 750 ml = ? fl oz

750 ml X 1 fl oz 1 29.6 ml 25.3 fl oz

LecturePLUS Timberlake

How many minutes are in 2.5 hours?

Initial unit

2.5 hr

Conversion Final

factor unit

2.5 hr x 60 min = 150 min

1 hr

cancel Answer (2 SF)

What is wrong with the following setup?

1.4 day x 1 day x 60 min x 60 sec

24 hr 1 hr 1 min

How many seconds are in 1.4 days?

1.4 day x 1 day x 60 min x 60 sec

24 hr 1 hr 1 min

Units would be = day2(sec)/hr2

Not the final unit needed

How many seconds are in 1.4 days?

Topic 1.2 really starts here

Measuring Matter

• By counting simply a number or moles

• By determining the mass grams

• By determining the volume liters

Not these!

Not this!

The Mole

• the mole is a unit used in chemistry to represent a large number of particles such as…• atoms (Ne, Ar…)• molecules (H2O, CO2…)• ionic compounds (NaCl, MgCl2…)• ions (Mg2+, Cl1-…)• similar to a dozen, except instead of 12,

it’s 602 billion trillion• 6.02 x 1023 or 602,214,199,000,000,000,000,000

• known as Avogadro’s number

1 dozen cookies = 12 cookies1 mole of cookies = 6.02 X 1023 cookies

1 dozen cars = 12 cars1 mole of cars = 6.02 X 1023 cars

1 dozen Al atoms = 12 Al atoms1 mole of Al atoms = 6.02 X 1023 atoms

Note that the NUMBER is always the same, but the MASS would be very different!

Mole is abbreviated mol (gee, that’s a lot quicker to write, huh?)

1 mole C 6.02 x 1023 C atoms

1 mole water 6.02 x 1023 H2O molecules

1 mole NaCl 6.02 x 1023 NaCl ionic compounds

(formula units)

• 6.02 x 1023 Na+ ions

• 6.02 x 1023 Cl– ions

for counting in chemistry, the conversion factor will be:

1 mole 6.02 x 1023 particles

OR 6.02 x 1023 particles

1 mole

Note that a particle could be an

atom OR a compound OR a

molecule!

Number of particles to moles

• How many moles in 5.68 x 1025 fluorine molecules?

5.68 x 1025 F2 molecules x _____1 mole____

1 6.02 x 1023 molecules = 94.4 mol F2

• How many moles of water in 7.77x1024 molecules of water?

• 7.77 x 1024 molecules H2O x 1mole

6.02x1023 molecules

• = 12.9 moles H2O

Number of moles to particles

• How many atoms in 5.59 moles of He?

5.59 moles He x 6.02 x 1023 atoms 1 1 mole

= 3.36 x 1024 atoms

• How many atoms in 2.98 moles of H20 molecules? 2.98 moles x 6.02 x 1023 molecules H2O x 3 atoms 1 1 mole 1 molecule H2O

= 5.38 x 1024 atoms