The Mole Concept Introduction Number of Particles and Moles Topic 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

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) LecturePLUS Timberlake

How many seconds are in 1.4 days? 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

Topic 1.2 really starts here

Measuring Matter By counting By determining the mass simply a number or moles By determining the mass grams By determining the volume liters

Not these! The Mole Not this!

known as Avogadro’s number 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 cookies 1 mole of cookies = 6.02 X 1023 cookies 1 dozen cars = 12 cars 1 mole of cars = 6.02 X 1023 cars 1 dozen Al atoms = 12 Al atoms 1 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 1 mole water 1 mole NaCl 6.02 x 1023 C atoms 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

Note that a particle could be an atom OR a compound OR a molecule! for counting in chemistry, the conversion factor will be: 1 mole 6.02 x 1023 particles OR

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