View
218
Download
1
Category
Preview:
Citation preview
The Mole ConceptThe Mole Concept
Chapter 9
CHM 130
GCC
9.1 Avogadro’s Number and The Mole
Eggs come in dozens = convenient
12 = dozenAtoms come in moles
6.02 x 1023 = mole = NA
NA is just a super large number
The MoleThe Mole One mole of softballs would be the size of the Earth! But atoms are so tiny that one mole of atoms is
about a handful. The mass of a mole of atoms = the atomic mass in
grams in the Periodic Table1 mole of C atoms is 12.01 grams1 mole of Na atoms is 22.99 grams
sulfur
water
mercury
sodium chloride
copper
lead
sugar
Mole Examples
1. How many calcium atoms are in 0.250 moles of calcium:
2. Calculate the moles of 3.75 x 1027 molecules of oxygen gas:
9.2 Avogadro’s number :
6.02 x 1023 atoms or mlcls or 1 mol 1 mol 6.02 x 1023atoms or mlcls
0.250 mol Ca (6.02 x 1023 atoms/mol) = 1.51 x 1023 Ca atoms
3.75 x 1027 mlcls O2 ( mol/6.02 x 1023 mlcls) = 6230 mol O2
Periodic Table masses are in ( g /mol )
How many grams in one mole of
carbon?
gold?
sodium?
Note = these are all 6.02 x 1023 atoms!
9.3 Molar Mass:
12.01 g/mol
196.97 g/mol
22.99 g/mol
Calculate the molar mass of barium
hydroxide.
1.What is the formula?
2.Add up the mass for every atom.
Molar Mass:
Ba(OH)2
137.33 + 2 ( 16.00) + 2 ( 1.01 ) = 171.35 g / mol
Very important – the units are grams per 1 mole, not just grams
9.4 Grams to Moles & Vice Versa9.4 Grams to Moles & Vice Versa
Use Molar Mass as (g / mol) or (mol / g) How many grams is 1.667 moles of oxygen gas? How many moles is 45 grams of silver? How many grams is 0.0554 moles of water?
1.667 mol O2 ( 32.00 g/mol) = 53.34 g O2
45 g Ag ( mol/ 107.87 g) = 0.42 mol Ag
0.0554 mol H2O (18.02g /mol) = 0.998 g H2O
9.5 Molar Volume (V of 1 mole at STP)
Volume of 1 mole of gasVolume of 1 mole of gas
Gases are mostly empty space so they ALL have the same volume despite different mass
22.4 L per 1 mole of any gas at STP STP is Standard Temperature and Pressure
0°C and 1 atm
For Gases only at STP: 22.4 L / 1 mol or 1 mol / 22.4 L
What is the mass of 4.50 L of chlorine gas at STP?
4.50 L Cl2 (mol / 22.4L) (70.90 g/mol) = 14.2 g Cl2
What is the volume of 1.25 moles of gas at STP?
1.25 mol ( 22.4 L / 1 mol) = 28.0 L gas
DensityDensity
d = = memolar volu
massmolar
volume
mass
Calculate the density of ammonia gas, NH3, at STP.
d = (17.04 g/mol ) / ( 22.4 L/mol ) = 0.761 g/L
9.6 Mole Calcs
ExampleExample
How many grams does 17.35 liters of neon gas mass at STP? How many atoms is this?
17.35 L = 15.6 grams Ne
mol 1
g 20.18
L 22.4
mol 1
mol 1
atoms10 x 6.02
L 22.4
mol 1 23
17.35 L = 4.66x1023 atoms Ne
Percent CompositionPercent Composition = mass % of each element in a compound Water is basically 11% H and 89% O You divide the total element molar mass by the total
compound molar mass. %H = (2.02 g H / 18.02 g H2O) x 100 = 11.2% H %O = (16.00 g O / 18.02 g H2O) x 100 = 88.79% O Note the %’s should add up to 100% total
Example ProblemExample Problem Find the percent composition for TNT, C7H5(NO2)3
Total molar mass is 227.15 grams per mole
% C = (84.07g / 227.15g) x 100 = 37.01% C% H = (5.05g / 227.15g) x 100 = 2.22%H% N = (42.03g / 227.15g) x 100 = 18.50%N% O = (96.00g / 227.15g) x 100 = 42.26%O
Try at homeTry at home How many liters will 3.425 grams of carbon dioxide
gas occupy at STP? 1.74 L How many molecules are in 3.425 grams of carbon
dioxide? 4.68 x 1022 molecules How many grams will 3.0 x 1015 molecules of carbon
dioxide mass? 2.2 x 10-7 grams
Self TestSelf Test
Page 258 Try 1-7, 10-13 Answers in Appendix J
Recommended