The Mole Chapter 10. How do you measure? Often measure something by one of three different methods- ...

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



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



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:



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



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?

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





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



Converting Mass to Moles

Given a massConvert to moles



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



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





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



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



The Mole Road Map



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



Percent Composition from Mass Data



Use of analytical procedures to determine the relative masses of each element in the compound and calculate the percent composition

Percent Composition from the Chemical FormulaIf you know the formula you can calculate

the percent composition using the following





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.

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).





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



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

Molecular Formula

Either the same as its empirical formulaOr a simple whole number multiple of its

empirical formula



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