Dimensional Analysis, the Mole Concept, and Avogadro’s Constant Topic 1.1

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 sec 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 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 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

1.4 day x 1 day x 60 min x 60 sec 24 hr 1 hr 1 min Units = day 2 /hr 2 Not the final unit needed

Topic 1.1 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 (H 2 O, CO 2 …) ionic compounds (NaCl, MgCl 2 …) ions (Mg 2+, Cl 1- …) similar to a dozen, except instead of 12, it’s 602 billion trillion 6.02 x 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 cookies 1 dozen cars = 12 cars 1 mole of cars = 6.02 X cars 1 dozen Al atoms = 12 Al atoms 1 mole of Al atoms = 6.02 X 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 C atoms 1 mole water  6.02 x H 2 O molecules 1 mole NaCl  6.02 x NaCl ionic compounds 6.02 x Na + ions 6.02 x Cl – ions

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

Number of particles to moles How many moles in 5.68 x fluorine molecules? 5.68 x molecules x _____1 mole____ x molecules = 94.4 mol F 2

How many moles of water in 7.77x10 24 molecules of water? 7.77 x molecules x 1mole 6.02x10 23 molecules = 12.9 moles H 2 O

Number of moles to particles How many atoms in 5.59 moles of He? 5.59 moles x 6.02 x atoms 1 1 mole = 3.36 x atoms How many atoms in 2.98 moles of H 2 0 molecules ? 2.98 moles x 6.02 x molecules H 2 O x 3 atoms 1 1 mole 1 molecule H 2 O = 5.38 x atoms