Chapter 11.1 The Mole
Mole SI base unit to measure the amount of a substance Equal to Avogadro's number (N A ) (6.02 x 10 23 ) of things i.e. atoms, pennies, pencils, etc.
The Mole A counting unit Similar to a dozen, except instead of 12, it s 602 billion trillion 602,000,000,000,000,000,000,000 6.02 X 10 23 (in scientific notation) This number is named in honor of Amedeo Avogadro (1776 1856), who studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present
Just How Big is a Mole? Enough pop 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.
Converting Moles to Particles # of moles x 6.02 x 10 23 particles 1 mole Practice Problems p. 311
Assignment Determine the number of representative particles for each of the following: 11.5 mol Ag 18 mol water 0.15 mol NaCl 3.75 mol Fe 12.5 mol CaCO3 How many moles of CaCl 2 contains 1.26 x 10 24 formula units of CaCl 2 How many moles of Ag contains 4.59 x 10 25 formula units of Ag
Chapter 11.2 Molar Mass
Molar Mass The Mass of 1 mole (in grams) Equal to the numerical value of the average atomic mass (get from periodic table) 1 mole of C atoms = 12.0 g 1 mole of Mg atoms = 24.3 g Some people used to call this a (gram formula mass) when used with ionic compounds
Find the molar mass (round to the tenths place) A.1 mole of Br atoms = 79.9 g/mole B.1 mole of Sn atoms = 118.7 g/mole
Molar Mass of Molecules and Compounds Mass in grams of 1 mole equal numerically to the sum of the atomic masses 1 mole of CaCl 2 = 111.1 g/mol 1 mole of N 2 O 4 = 92.0 g/mol
Converting Moles to Grams grams = moles X molecular mass 2 moles of CuSO 4 = g G = 2 x 159.6 = 319.2 g
Converting Grams to Moles moles = grams molecular mass 779 g CuSO 4 = mol Mol = 779/159.6 = 4.88 moles
Atoms/Molecules and Grams Since 6.02 X 10 23 particles = 1 mole AND 1 mole = molar mass (grams) You can convert atoms/molecules to moles and then moles to grams! (Two step process)
Atoms/Molecules and Grams You can t go directly from atoms to grams!!!! You MUST go thru MOLES. That s like asking 2 dozen cookies weigh how many ounces if 1 cookie weighs 4 oz? You have to convert to dozen first!
Converting Grams to Atoms # grams/molar mass x N A
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 10 23 atoms Cu 63.5 g Cu 1 mol Cu = 3.4 X 10 23 atoms Cu
How many atoms of K are present in 78.4 g of K? 78.4 g K 1 mol K 6.02 X 10 23 atoms K 39.1 g K 1 mol K = 1.20 X 10 24 atoms K
Converting Atoms to Grams # atoms/n A x Molar Mass
1.2 x 10 25 atoms of N = g 1.2 x 10 25 x 14 = 279.1 6.02 x 10 23
Assignment Get a book Questions 11-19
Chapter 11.3 Molar Relationships
Molar Mass Sum of the molar masses of the component elements In one mole of a compound, the ratio of moles of each element is the same as for one molecule (p.321 20-24)
Chapter 11.4 Percent Composition and Formulas
Percent Composition Percent by mass of each element in a compound Mass of Element Mass of Compound x100=%mass
Percent Composition Fe 2 O 3 = 160 g Fe= 56 x 2 = 112 g O = 16 x 3 = 48 g 112/160x100 = 70% 48/160x100 = 30% CaCl 2 H 3 PO 4
Chemical Formulas of Compounds Formulas give the relative numbers of atoms or moles of each element in a formula unit - always a whole number ratio (the law of definite proportions). NO 2 ; 2 atoms of O for every atom of N 1 mole of NO 2 = 2 moles of O atoms to every 1 mole of N atoms
Chemical Formulas of Compounds If we know or can determine the relative number of moles of each element in a compound, we can determine a formula for the compound.
Empirical Formula The formula of a compound that expresses the smallest whole number ratio of the atoms present. Ionic formula are always empirical formula May or may not be the same as the molecular formula
To obtain an Empirical Formula 1. Determine the mass in grams of each element present, if necessary. If the problem gives you a percent composition assume a 100 g sample 2. Calculate the number of moles of each element from the masses.
To obtain an Empirical Formula 3. Divide each by the smallest number of moles to obtain the simplest whole number ratio. 4. If whole numbers are not obtained * in step 3, multiply through by the smallest number that will give all whole numbers * Be careful! Do not round off numbers prematurely
Assignment A blue solid is 36.8% nitrogen and 63.2% oxygen what is the empirical formula? Determine the empirical formula for a compound that contains 36% aluminum and 64% Sulfur Propane is 81.8% carbon and 18.2% hydrogen, what is the empirical formula for propane? Aspirin is 60% carbon, 4.4% hydrogen, and 35.6% oxygen, what is the empirical formula of aspirin? Determine the empirical formula for a compound that contains 10.9% magnesium, 31.8% chlorine, and 57.3% oxygen
Molecular Formula The formula that states the actual number of each kind of atom found in the compound Necessary since multiple compounds can have the same empirical formula Molecular Formula = Empirical Formula x factor by which everything is multiplied
Determining Molecular Formula 1. Calculate the empirical formula 2. Calculate the empirical formula mass by multiplying number of moles by molar mass 3. Divide the given molar mass by the mass of the empirical formula 4. Multiply subscripts in the empirical formula by the answer in #3
Assignment Page 335 &337, # s 51-62
Chapter 11.5 Hydrates
Hydrate Solids that contain water molecules Each hydrate has a specific number of water molecules Anhydrous Water has been removed from a hydrate
Uses for Hydrates Used to store solar energy Anhydrous materials are used as desiccants
Naming Hydrates # of water molecules follows the solid formula and a dot MgSO 4 4H 2 O Prefixes for water are on page 338 Mass of water must be included in all calculations
Determining the Formula of a Hydrate Write the formula for the solid Determine the mass of the water (Original mass anhydrous mass) Calculate the moles of water (mass/18g) Calculate the moles of compound Determine the amount of water (mol H 2 O/mol compound) Rewrite formula
Determining the Formula of a Hydrate If 2.50 g of copper sulfate reduces to1.59 g after heating what is the formula for the copper sulfate Hydrate? 1. CuSO 4 _ H 2 O 2. 2.50 g 1.59 g = 0.91 g 3. 0.91g/18g = 0.05 mols 4. 1.59g/160g = 0.01 mols 5. 0.05/0.01 = 5:1 6. CuSO 4 5 H 2 O
Assignment Find the formula for the following hydrates: 48.8% MgSO 4 and 51.2% H 2 O An 11.75 g sample of cobalt (II) chloride hydrate is heated, 9.25 g of anhydrous cobalt chloride remains. What is a hydrate? Describe the experimental procedure for finding the formula of a hydrate. Name the compound having the formula SrCl 2 6H 2 O Arrange these hydrates in order of increasing percent water content: MgSO 4 7H 2 O, Ba(OH) 2 8H 2 O, CoCl 2 6H 2 O