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CHEMISTRY 161 Chapter 4 The Mole. Macroscopic versus Microscopic Worlds. 2 H 2 + O 2 2 H 2 O. 1 liter water contains about 3.3 X 10 25 molecules. CHEMICAL MASS SCALE. standard / calibration. atomic mass unit (amu, u). one atom of carbon-12 12 u (exactly). - PowerPoint PPT Presentation
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Macroscopic versus Microscopic Worlds
2 H2 + O2 2 H2O
1 liter water contains about 3.3 X 1025 molecules
CHEMICAL MASS SCALE
standard / calibration
atomic mass unit (amu, u)
one atom of carbon-12 12 u (exactly)
we have to correlate u with kg
CaO
O: 15.999 u
Ca: 40.08 u
CaO: 56.08 u
formula mass: weight of one molecule
correlation between u and kg
one mole of a compound contains the same number of molecules/atoms as the number of atoms
in exactly 12 g of 12C
Avogadro’s numberNa
6.023 x 1023
1 mole of H2O 6.023 x 1023
1 mole of 12C
6.023 x 1023
6.023 x 10231 mole of NaCl
1 mole of Na
6.023 x 1023
Avogadro’s numberlinks micro and
macroscopic world
molecules
molecules
atoms
atoms
1 mole of H2O 6.023 x 1023 molecules
1 molecule of H2O – 2 H atoms and 1 O atom
1 mole of H2O – 2 mole H atoms and 1 mole O atoms
6.023 x 1023 molecules of H2O
6.023 x 1023 atoms of O
2 x 6.023 x 1023 atoms of H
H2OO: 15.999 u
H: 1.008 u
H: 1.008 u
H2O: 18.015 u
1 mole of H2O – 18.015 g
15.999 g/mol
1.008 g/mol
1.008 g/mol
Na
Na
Na
1 mole of H2O – 18.015 g
6.023 x 1023 molecules of H2O – 18.015 g
one molecule of H2O – 2.99 x 10-23 g
molecular weight of one mole of H2O 18.015 g mol-1
2 H2 + O2 2 H2O
2 molecules 1 molecule 2 molecules
2 moles 1 mole 2 moles
4.03176g 31.9988g 36.03g
STOICHIOMETRY
x g y g 70.0g
2 H2 + O2 2 H2O
2 molecules 1 molecule 2 molecules
2 moles 1 mole 2 moles
4.03176g 31.9988g 36.03g
STOICHIOMETRY
x g y g 70.0g
Example I: How many grams of iron are in a 15.0 g
sample of iron(III) oxide?
1. molecular formula
3. weight of one mole Fe2O3
2. weight of one molecule
Fe2O3
159.7 u
159.7 g4. 1 molecule Fe2O3 contains 2 atoms of Fe
5. 1 mole Fe2O3 contains 2 moles of Fe
159.7 g 111.69 g
15.0 g x gx = 10.5 g
Example II: How many grams of oxygen are in a 10.0 g
sample of nickel (II) nitrate?
1. molecular formula
3. weight of one mole Ni(NO3)2
2. weight of one molecule
4. 1 molecule Ni(NO3)2 contains 6 atoms of O
5. 1 mole Ni(NO3)2 contains 6 moles of O
x = 5.25 g
Example III:
How many atoms are in 10 kg of sodium?
1 mole sodium = 22.98977 g
6.023 x 1023 atoms = 22.98977 g
x atoms = 10,000 g
x = 2.6 x 1026 atoms
Example IV
How heavy are 1 million gold atoms?
1 mole gold = 196.96654 g
6.023 x 1023 atoms = 196.96654 g
1,000,000 atoms = x g
x = 3.2 x 10-16 g = 0.32 fg
Mass Percentage Composition
moles of elementmoles in whole sample% mole 100%
P4O10
100% element % sample wholeof masselement of mass
= X 100 %
= X 100 %
Example V
A sample was analyzed and contains 0.1417 g of nitrogen and 0.4045 g of oxygen.
Calculate the percentage composition.
1. mass of whole sample
100% element % sample wholeof masselement of mass
2. percentages of elements
= X 100 %
Example
A sample contains 0.522 g of nitrogen and 1.490 g of oxygen. Calculate its empirical formula.
N2O5
COMBUSTION
C3H8 CO2 + H2O
0.013068 g
+ O2
How many grams of oxygen are consumed?
1.balance equation
2.convert to moles
The combustion of a 5.217 g sample of a compound of C, H, and O gave 7.406 g
CO2 and 4.512 g of H2O.
Calculate the empirical formula of the compound.
How many grams of Al2O3 are produced when 41.5 g Al react?
2Al(s) + Fe2O3(s) Al2O3(s) + 2 Fe(s)
How many grams of NO can form when 30.0 g NH3 and 40.0 g O2 react according to
4 NH3 + 5 O2 4 NO + 6 H2O
2 C2H2 + 5 O2 4 CO2 + 2 H2O