the mole theory. dimensional analysis a way to solve problems by converting or using the units of...
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The Mole TheoryThe Mole Theory
Dimensional AnalysisA way to solve problems by
converting or using the units of the items involved
Converting one thing to the another – amount has not changed
Conversion factors: the numerator and denominator are equal so they are basically equal to ‘1’ – used to solve for unknowns in dimensional anaylsis problems
Dimensional Analysis
Problem Problem 11::How many seconds are in a day?
secday
What do we know? Set up Conversion Factors:
Let’s solve.
×× = 86,400 sec 1 day
Dimensional AnalysisProblem 2:You're throwing a pizza party for 15 and figure each
person might eat 4 slices. How much is the pizza going to cost you? You call up the pizza place and learn that each pizza will cost you $14.78 and will be cut into 12 slices. You tell them you'll call back. How much money is the pizza going to cost you, which in math terms is: cost (in dollars) per party, or just $/party
14.78 x 4 x 15 = $73.90 12 party
How do you measure How do you measure matter?matter?
- Counting (dozen, 3/$1, 6 pack)
- Mass ( 1 lb, 4 oz, 57g)
- Volume (liter, gallon, pint, quart)
In chemistry- this is all measured In chemistry- this is all measured by a measuring unit called the by a measuring unit called the
mole.mole.
Mass of a MoleMass of a Moleo Molar Mass- the mass of a mole of
any element or compound (in grams)
o Also called:oFormula mass – sum of the atomic
masses of all the atoms in a formula of a compoundo 1 Mole = Molar Mass
oConversion Factors:1 Mole OR Molar MassMolar mass 1 Mole
How to determine molar How to determine molar mass-mass-
The atomic mass expressed in grams- rounded to whole number (ones place)
Examples: C = Cl = O = F =
12g
35g
16g
19g
For compounds- Add together all the atoms that make up the compound
Examples:• SO3 =
How to determine molar How to determine molar mass-mass-
1 S atom
3 O atoms
32g + 16g + 16g + 16g = 80g
What is the gram formula mass of ammonium carbonate (NH4)
2CO3?Take inventory:
◦N- 2 × 14 = 28◦H- 8 × 1 = 8◦C- 1 × 12 = 12 ◦O- 3 × 16 = 48
96g
How to determine molar How to determine molar mass-mass-
Number of particles in a Number of particles in a MoleMole
What is a representative particle? How the substance normally exists:How the substance normally exists:
1 mole = 6.02 × 10 23 representative particles(also called Avogadro’s Number)(also called Avogadro’s Number)
1.Atom- rep. particle for most elements2.Molecule- rep. particle for covalent
compounds and diatomic molecules “BrINCl HOF”
3.Formula unit- rep. particle for ionic compounds
Converting from moles –› Converting from moles –› particlesparticlesAnalogy:1 dozen = 12
eggs
Conversion Factors:
1 dozen or12 eggs
12 eggs1 dozen
For moles and particles:1 mole = 6.02 × 1023 rep particles–
therefore
Conversion Factors1 mole OR6.02 × 1023 particles
6.02 × 1023 particles1 mole
How to solve mole How to solve mole problems:problems:
1. Determine known and unknown.Known: 1.25 × 1023 atoms MgUnknown: moles
2. Determine the conversion factor(s) needed.
3. Multiply the known by the appropriate conversion factor(s) so units cancel.
4. Calculate answer2.08 × 10-1 moles or .208 moles
6.02 × 1023 particles1 mole
or
1.25 × 1023 atoms Mg 1 mole
6.02 × 1023 atoms
How many moles are in the number of molecules? Sample problem: 1.25 × 1023 atoms Mg
1 mole6.02 × 1023 particles
The Mole and Avogadro’s The Mole and Avogadro’s NumberNumber
How many molecules are in 2.0 moles?
2.0 mol6.02 1023
molecules
1 mol= 1.20 1025
molecules
How many moles are in 6.02 × 1023 ?
6.02 × 1023 particles 1 mol
6.02 × 1023 particles
= 1 mol
The Mole and Avogadro’s The Mole and Avogadro’s NumberNumber
Volume of a Mole of GasVolume of a Mole of GasThe Volume of a gas varies with a
change in temperature or pressure.Measured at standard temperature and pressure (STP)
0°C at 1 atmosphere (atm)
1 mole of any gas occupies a volume of 22.4L
Conversion Factors:1mole OR 22.4 L22.4 L 1 mole
All the conversion factors you All the conversion factors you need to know!need to know!
Representative Particles1 mole
6.02 × 1023 particles
6.02 × 1023 particles1 mole
Mass 1 Mole OR Molar MassMolar mass 1 Mole
OR
1 mole OR 22.4 L22.4 L 1 mole
Volume
Molar Conversion Molar Conversion ExamplesExamples
Find the mass of 2.1 1024 molecules of NaHCO3.
2.1 1024
molecules 1 mol
6.02 1023
molecules
= 290 g NaHCO3
84.01 g
1 mol
Your clothing labels have Percent Composition.
Percent CompositionPercent CompositionThe percent by mass of each element
in a compoundInformation needed:
◦Formula of the compound◦Gram atomic mass of its elements
% mass = grams of element in 1 mol compound × 100 molar mass of compound
Calculating % Calculating % CompositionCompositionCalculate the % composition of
C3H8.
% C = mass of C × 100
= 36g X 100% = 0.818181 = 81.8%
44g% H = mass of H × 100
= 8g × 100% = 0.181818 = 18%
grams of compound
grams of compound
44g