the mole chapter 10. how do you measure? often measure something by one of three different methods- ...
TRANSCRIPT
The Mole
Chapter 10
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How do you measure?
Often measure something by one of three different methods- by counting by mass by volume
How about them apples
By count: 1 dozen = 12 applesBy mass: 1 dozen = 2.0 kg of applesBy volume: 1 dozen = 0.2 bushels To do this you must use conversion
factors
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Practice Problems
If 0.20 bushel is 1 dozen apples & a dozen apples has a mass of 2.0 kg, what is the mass of 0.50 bushel of apples?
Assume 2.0 kg of apples is 1 dozen and that each apple has 8 seeds. How many apple seeds are in 14 kg of apples?
What is a mole?
6.02 x1023 also known as Avogadro’s number
602,000,000,000,000,000,000,000Considers the very small size of atomsHelps with the conversion of units
But What is a Mole???
6.02x1023 representative particles are in each and every mole
SI unit of measuring the amount of a substance
Representative particle
AtomsMoleculesFormula units
A mole of any substance contains Avogadro’s number of representative particles
Converting Number of particles to moles
Equation
This equation can be placed in a unit conversion to find the number of particles
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Practice Problem
Magnesium is a light metal used in the manufacture of aircraft, automobile wheels, tools and garden furniture. How many moles of magnesium is 1.25 * 10 23 atoms of magnesium?
Converting Moles to Number of Particles
Determining how many atoms are in one mole of a compound
This number is discovered from the formula:
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Molecules and Atoms
How many moles are in one CO2
molecule?A mole of CO2 of contains 1 Avogadro’s
number of carbon dioxide moleculesHowever, there are 3 atoms in every 1
molecule of carbon dioxide So, there are 3 moles worth of atoms in every
1 moles worth of carbon dioxide molecules
Converting Moles to Number of Particles
To find the number of atoms, molecules, representative particles in a mole of a compound, you must first determine the number of representative particles, then you can use the following equation
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Practice Problems
Propane is a gas used for cooking & heating. How many atoms are in 2.12 mole of propane (C3H8)?
The mass of a mole of an element
The atomic mass of a single atom is expressed as atomic mass units
Atomic mass units is the atomic mass expressed in grams
What is the atomic
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Molar Mass of an element
Mass of one mole of an elementExample:
1 mole of gold weighs 196 g What is the mass of 1 mole of Magnesium?
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Pop Quiz What is the molar mass of oxygen?
What is the molar mass of carbon?
What is the molar mass of hydrogen?
Molar Mass
To calculate the molar mass of a compound: Find the number of grams of each element in
one mole of the compound. Then add the masses of the elements in the
compound
Applies to ionic & molecular compoundsEx: Carbon Dioxide (CO2) 44 g/mol
Finding Molar Mass of Sulfur Trioxide
Determine how many atoms of each element are in the compound
Add up the masses of all the atoms
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Mole-Mass and Mole-Volume Relationships10.2
Mole to Mass Relationship
Molar Mass = mass of 1 mole of a substance
We can determine the mass of a substance through the number of moles it contains
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Practice Problem
Determine the mass of 5 moles of NaCl. Use the following equation
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Converting Mass to Moles
Given a massConvert to moles
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The Mole-Volume Relationship
Avagadro’s hypothesis: Equal volumes of gases at
the same temperature and pressure contain equal number of particles
Change in temperature or pressure will change the volume
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Figure 10.9 In each container, the volume occupied by the gas molecules is small compared with the container ユ s volume, so the molecules are not tightly packed. a. The molecules in this container are small. b. This container can accommodate the same number of larger molecules.
Change in Temperature
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Standard Temperature & Pressure (STP)
We usually measure volume at STP Temperature: 0oC Pressure: 101.3 kPa or 1 atm
At STP, 1 mol or 6.02x1023
rep particles, of any gas
occupies a volume of 22.4L22.4L = molar Volume
Calculating Volume at STP
Molar volume can be used to convert the known number of moles to the volume of a gas at STP
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Calculating Molar Mass from Density
Density of a gas at STP and the molar volume at STP (22.4L/mol) can be used to calculate the molar mass of a gas
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The Mole Road Map
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Percent Composition and Chemical Formulas10.3
Percent Composition
Relative amounts of elements in a compound Also known as the percent by mass of each
element in the compound
We can use a simple formula to determine % composition
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Percent Composition from Mass Data
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Use of analytical procedures to determine the relative masses of each element in the compound and calculate the percent composition
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Percent Composition from the Chemical FormulaIf you know the formula you can calculate
the percent composition using the following
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Figure 10.14 The percent composition of water is always the same regardless of the volume of the water sample. A sample of water is always 11.1% H and 88.9% O by mass.
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Percent Composition as a Conversion FactorUse percent composition to calculate the
number of grams of any element in a specific mass of a compound
Multiply mass of compound by a conversion factor based on the percent composition
Practice Problem
How much C & H are in 82.0 g of propane You found that propane is 81.8% C and 18% H. That means that in a 100-g sample of propane,
you would have 81.8 g of C and 18 g of H. You can use the ratio
to calculate the mass of carbon contained in
82.0 g of propane (C3H8).
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Empirical Formula
Lowest whole number ratio of the atoms of the elements in a compound
Example: H2O2 or Hydrogen Peroxide The ratio is 1:1 even though there are two
atoms of each element in the compound
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Calculating Empirical Formula
Convert your percent and express as moles
Convert from grams to moles using your mole ratio
Divide each by the lower number of moles
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Molecular Formula
Either the same as its empirical formulaOr a simple whole number multiple of its
empirical formula
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