The Mole iew_video.php?viewkey=accb 4798ce8a9857e3f6 1
Real World Chem Real chemists don’t realistically work with individual atoms and molecules. Even a small sample of a substance contains BILLIONS or TRILLIONS of atoms or molecules To keep track of how many atoms, molecules, compounds, etc. they were working with, scientists came up with the “mole” 2
What is a Mole? 3
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SI Counting Unit in Chemistry The mole is the standard counting unit in chemistry (abbreviated “mol”) Just as a dozen eggs equals 12 eggs… A mole = 602,000,000,000,000,000,000,000 Or 602 billion trillion Or 6.02 X (in scientific notation) 5
The Mole 6 1 dozen = 12 1 gross = ream = mole = 6.02 x 10 23
Avogadro’s Number Not Avocado 6.02 X is also known as Avogadro’s Number Named after Italian chemist Amadeo Avogadro who determined that at the same temp and pressure, all gasses contained the same number of particles 7
Just How Big is a Mole (6.02 x )? 8 Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles. If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles. If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.
What is a mole? It is also the number of atoms in the atomic mass in g of any element. Look at your periodic table, the atomic mass of Oxygen is 16 g. This is NOT the mass of 1 oxygen atom. It is the mass of 1 mole (or 6.02 x ) oxygen atoms 9
Also… What is a mole? the number of molecules in the molecular weight, in grams, of any compound. the number of molecules in 18 g of water (H 2 O – if you add up the masses of 2 hydrogens and a water it equals 18g) There are 6.02 x molecules of water in 18g of water. 10
What Can Be Expressed Using Moles? A mole can be used to represent 6.02 x : -atoms -molecules -ions -compounds -particles -items -formula units 11
The Mole 12 11 dozen cookies = 12 cookies 1111 mole of cookies = 6.02 X 1023 cookies 11 dozen cars = 12 cars 1111 mole of cars = 6.02 X 1023 cars 11 dozen Al atoms = 12 Al atoms 1111 mole of Al atoms = 6.02 X 1023 atoms Note that the NUMBER is always the same, but the MASS is very different!
A Mole of Particles Contains 6.02 x particles 1 mole C = 6.02 x C atoms 1 mole H 2 O = 6.02 x H 2 O molecules 1 mole NaCl = 6.02 x NaCl “formula units” 13
How do we use the mole? We’d never use the mole to describe macroscopic or real world objects. 1 mole (6.02x10 23 ) of watermelon seeds would be found inside a watermelon the size of the moon. 1 mole (6.02x10 23 ) of donut holes would cover the earth and would be 5 miles deep. Since the mole is such a huge number of items, it is only used to describe the amount of things that are very, very small. 1 mole (6.02x10 23 ) of water molecules would barely fill a shot glass 14
Avogadro’s Number as Conversion Factor x (small unit) = 1 mol can be used to solve problems by putting it in ratio form x (unit) 1 mole or 1 mole 6.02 x (unit)
Converting Moles Molecules 16
Converting Moles Molecules Use Avogadro’s constant (6.02 x unit) when converting between moles and molecules. EX: How many atoms are in 3.4 moles of iron atoms? Follow these steps… 17
Calculation 1. Start with known value divided by 1. 2. Then line up units so that only the desired units are not cancelled. 3. Divide the products of the numerators by the products of the denominators. 4. Express answer in correct sig figs and unit. 3.4 moles 6.02 x atoms = 2.0 x moleatoms 18
Number of moles of S in 1.8 X atoms. Learning Check 1.8 X atoms S 1 mole S 6.02 x atoms S = 3.0 moles S 1 19
Number of atoms in mole of Al Learning Check mole Al 1 mole Al 6.02 x atoms Al = 3.01 X atoms Al 1 20
Number of pieces in 2 moles of M&Ms Learning Check 2 moles M&Ms 1 mole M&Ms 6.02 x pieces = 1 X pieces 1 Last slide 21
The Mole Part 2 22
Calculating molar Mass 23
How do we measure moles? Do you know how to measure out 1 mole of sugar or salt or water? The mole is a counting unit, so we would have to count out 6.02 x particles of each substance. (NO THANKS!) There are 2 ways to measure out a number of moles of a substance: Measure it in GRAMS ( a mass) Or measure it in LITERS ( a volume) 24
Using mass to measure moles… To be able to measure out 1 mol of a substance… we would need to know the mass in grams of 1 mol of the substance in question. Since each atom is a different size and has a different mass, 6.02 x of each atom would weigh a different amount. Remember, we don’t use Avogadro’s number to count anything but atoms, molecules, etc. So we need a table that provides the mass 1 mole would weigh for every combination of atoms known to man. 25
Using mass to measure moles… It just so happens that the periodic table provides us with that information. The masses of each atom on the table is the equivalent to the mass of 1 mole of that atom. The mass on the periodic table is called the molar mass (units of g/mol), because it represents the mass of 1 mol of that atom 1 mole of Mg atoms weighs g 1 mole of C atoms weighs g 26
Calculating Molar Mass Molar mass is the mass of 1 mole of a pure substance. Unit (label) = g/mol Molar mass may also be referred to as: -gram formula mass (ionic compounds) -formula mass (ionic compounds) -molecular mass (non metals) 27
Calculating Molar Mass EX: Find the molar masses for the following: Silver Argon Potassium Oxygen Hydrogen g/mol g/mol g/mol g/mol 1.01 g/mol 28
Using mass to measure moles… That works well for atoms off of the periodic table, but how do we find the molar mass of molecules and compounds? Each of those compounds and molecules are composed of a combination of atoms. We have the molar masses for all of the atoms on the periodic table. We need to be able to add up the total weight of all of the atoms in the compound or molecule given its formula. For example, what is the molar mass of H 2 O? 29
Calculating Molar Mass The molar mass of a molecule or formula can be determined by adding the molar masses of each of the elements present. EX: H 2 O Elements Moles of each Atomic mass H 2 x 1.01 = 2.02 O 1 x =16.00 Molar mass of H 2 0 g/mol 30
Calculating Formula Mass 31 Calculate the formula mass of magnesium carbonate, MgCO g g + (3 x g) =84.32 g/mol Thus, 6.02 x MgCO 3 ’s would weigh grams
Calculating Molar Mass Calculate molar mass of the following: 1. Al 2 S 3 Al (2 x 26.98) = S (3 x 32.07) = g/mol Last slide 32
Converting Moles Grams (mass) 33
Mole Conversions We can use these molar masses in calculations in which we are either Given moles and asked for its mass equivalent or Given mass and asked for its mole equivalent. If we are given an element… we just use the mass from the periodic table If we are given a formula instead… we just calculate the molar mass of the molecule using the masses from the periodic table. 34
Mole Conversions The key to converting between any units is to label numeric values with appropriate units and work with these until the only one that will not cancel is the one you want. You now have the conversion bridge necessary to convert moles grams. 35
Conversion Steps 36 Step 1: Identify given (number and unit) and place it over 1. Step 2: Place the unit that needs to cancel in the denominator and its equivalent in the numerator. EX: 1 mol = 6.02 x molecules 1 mole = molar mass in grams
37 Step 3: Cancel units that are in the numerator and denominator. Step 4: Continue conversion steps until the only unit remaining is the unit you need. Step 5: Multiply all numbers in numerator. Step 6: Divide all numbers in the denominator. Step 7: Express answer with correct unit and sig figs. Conversion Steps
Converting Moles and Grams Ex: Ex: Aluminum is often used for the structure of light-weight bicycle frames. Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al? How many grams of Al are in 3.00 moles of Al? 3.00 moles Al ? g Al
1. Molar mass of Al 1 mole Al = g Al 2. Conversion factors for Al 26.98g Al or 1 mol Al 1 mol Al g Al 3. Setup 3.00 moles Al x g Al 1 1 mole Al Answer = = 80.9 g Al Mole Conversions
#1. What is the mass in grams of 2.5 mol of O 2 ? 2.5 mol O 2 x g O 2 = 80 = 1 1 mol O 2 80 g of O 2 #2. Determine the number of moles in 5.00 g of H 2 O g H 2 O x 1 mol H 2 O = = g H 2 O mol of H 2 O 40 Last slide
The Mole Part 3 41
Converting Moles Molecules & Converting Moles Grams (mass) 42 Review:
The Mole Because the mole measures both a mass and a number of particles (6.02 x = 1 mole = molar mass), it is the central unit in converting the amount of a substance from one type of measurement to another Understanding how to use the mole is essential to the study of chemistry 43
Sample Problems MOLES GRAMS Use Molar Mass 44 0.2 mol H 2 SO 4 molecules 1.2 x molecules of O 2 moles g CuCO 3 moles 2.5 moles of NaCl grams MOLES MOLECULES Use Avogadro’s #
Since 6.02 X particles = 1 mole AND 1 mole = molar mass (grams) You can convert atoms/molecules to moles and then moles to grams! (Two step process) You can’t go directly from atoms to grams!!!! You MUST go thru MOLES. 45 Atoms, Molecules & Grams
46 Mole Atoms or molecules Atoms or molecules Liters Grams 6.02 x AtomicMassAtomicMass L 22.4 L
Calculations molar mass Avogadro’s number Grams Moles Particles Everything must go through Moles!!!
Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? 35.4 g Cu 1 mol Cu 6.02 X atoms Cu g Cu 1 mol Cu = 3.36 X atoms Cu
Mole Conversions Now a challenge: Determine the number of molecules there are in a 5.45 g sample of CaCl g CaCl 2 x 1 mol CaCl 2 x 6.02 x molecules CaCl g CaCl 2 1 mol CaCl x molecules of CaCl 2 49
1. A sample of hydrochloric acid has 8.95 x molecules, how many grams is this? 2. If aluminum hydroxide has a mass of 150 grams, how many formula units are there? 50 Practice Problems (a mole is also known as… a formula units for ionic compounds) Aluminum hydroxide Hydrochloric Acid