the mole concept introduction number of particles and moles topic 1.2
TRANSCRIPT
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