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Unit 2 Lesson #5Avogadro’s Number
& The Mole (p.14-16)
How Big is A Mole?
A. What is the Mole?
1. A counting number (like a dozen)
2. Avogadro’s number (NA)
1 mole = 6.022 1023 representative particles
3. Using Dimensional Analysis to Make Conversions
a. Convert 48 eggs to dozens of eggs
Conversion factor :
48 eggs X 1 dozen
1 12 eggs
b. Convert 6 dozen to number of eggs
Conversion factor :
6 dozen X 12 eggs 1 1 dozen
4. Molar Conversion Factors
a. # of Particles (atoms, molecules, ions, etc.)1 mole = 6.022 1023 particles
b. Molar mass = mass of 1 mole of a substance
1 mole = molar mass
c. Molar Volume = 22.4 Liters for any gas at STP (Standard Temperature Pressure)
*STP = T = 0o C or 273 K P = 1.0 atmosphere (atm)
1 mole = molar volume
Mole Relationships
http://itschemistrytime.blogspot.com/2011_11_01_archive.html
Representative Particles & Moles
Substance Chemical Formula
Representative Particle
Rep Particles in 1.00 mole
Carbon C 6.02 x 1023
Nitrogen gas N2
Calcium ion Ca2+
Magnesium fluoride
MgF2 6.02 x 1023
Representative Particles & Moles
Substance Chemical Formula
Representative Particle
Rep Particles in 1.00 mole
Carbon C Atom 6.02 x 1023
Nitrogen gas N2 Molecule 6.02 x 1023
Calcium ion Ca2+ Ion 6.02 x 1023
Magnesium fluoride
MgF2 Formula unit 6.02 x 1023
B. Mole to Particle Conversions
MOLESNUMBER
OF
PARTICLES
6.022 1023
NA
(particles/mol) Particles = atoms, molecules, formula
units, ions, etcNA atoms/mol
NA molecules/mol
1. How many molecules are in 2.50 moles of C12H22O11?
2.50 molC12H22O11
6.02 1023
moleculesC12H22O11
1 mol C12H22O11
= 1.51 1024
molecules C12H22O11
2. If you have 2.23 x 1018 atoms of sodium, how many moles is that?
2.23 1018
atoms Na1 mole Na
6.02 1023
atoms Na
3.70 x 10-6
moles Na=
3. How many formula units is 3.75 moles of calcium hydroxide?
3.75 mol Ca(OH)2
6.02 1023
formula unitsCa(OH)2
1 mol Ca(OH)2
= 2.26 1024
formula units Ca(OH)2
1. Molar Mass = The mass of one mole of an
element or compound
Atomic mass (on the PT) tells the... mass of each atom (amu) grams per mole (g/mol)
2. Round to 2 decimal places
C. Molar Mass Conversions
3. Molar Mass Examples
a. carbon
b. aluminum
c. zinc
12.01 g/mol
26.98 g/mol
65.39 g/mol
4. Molar Mass Examples
a. water
b. sodium chloride
H2O
2(1.01) + 16.00
NaCl 22.99 + 35.45
= 18.02 g/mol
= 58.44 g/mol
5. Molar Mass Examples
a. sodium bicarbonate
b. sucrose
NaHCO3
22.99 + 1.01 + 12.01 + 3(16.00)
= 84.01 g/mol
C12H22O11
12(12.01) + 22(1.01) + 11(16.00)
= 342.34 g/mol
6. Molar Mass Examples
a. magnesium hydroxide
b. ammonium sulfate
Mg(OH)2
24.31 + 2(16.00) + 2(1.01)
= 58.33 g/mol
(NH4)2SO4
2(14.01) + 8(1.01) + 32.06 + 4(16.00) = 132.16 g/mol
D. Molar Mass Conversions
molar mass
(g/mol)
MASS
IN
GRAMS
MOLESNUMBER
OF
PARTICLES
6.02 1023
NA
(particles/mol)
Particles = atoms, molecules, formula
units, ions, etcNA atoms/mol
NA molecules/mol
1. How many moles of carbon atoms are in 26 g of carbon?
26 g C 1 mol C
12.01 g C= 2.2 mol C
2. Find the mass of 2.1 1024 molecules of NaHCO3.
2.1 1024
MoleculesNaHCO3
1 mol NaHCO3
6.02 1023
Molecules NaHCO3
= 290 g NaHCO3
84.01 g NaHCO3
1 mol NaHCO3
1 mol K
39.10 g K
3. How many atoms are in 22.5 grams of potassium?
6.02 1023
atoms K
1 mol K
= 3.46 x 1023 atoms K
22.5 g K
E. Molar Volume Conversions
Molar Mass
Molar Vol
NA
* Molar Volume = 22.4 Liters for any gas at STP
1. What is the volume at STP of 4.00 g of CH4?
4.0g X 1 mole X 22.4 L = 5.6 L 1 16 g 1 mole
2. How many grams of He are present in 8.00 L of He at STP?
8.0 L X 1 mole X 4.0 grams = 1.4 g 1 22.4 L 1 mole