# Unit 5 CHEMICAL QUANTITIES CHAPTER 10 – THE MOLE.

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Unit 5 CHEMICAL QUANTITIES CHAPTER 10 – THE MOLE

How much sand?

3 Ways to Measure Matter By COUNT – 1 million grains of sand By MASS – 1,000 grams of sand By VOLUME – 100 liters of sand

ATOMIC MASS: What is the atomic mass of Hydrogen? 1.01 a.m.u. What is the atomic mass of Oxygen? 15.999  16.0 a.m.u.

= + SO 3 1 S atom3 O atoms You can calculate the mass of a molecule by adding the atomic masses of the atoms making up the molecule. (32.1 + 16 + 16 + 16 = 80.1 amu)

What is the atomic mass of Water (H 2 O)? H – 2 (1.0) = 2.0 a.m.u. O – 1(16.0) =16.0 a.m.u. 18.0 a.m.u What is the atomic mass of CO 2 ? C – 1(12.0) = 12.0 a.m.u O – 2 (16.0) = 32.0 a.m.u. mass of CO 2 = 44.0 a.m.u. What is the atomic mass of Al 2 (SO 4 ) 3 ?

What is a MOLE? A mole is a quantity equal to Avogadro’s Number (6.02 x 10 23 ) 6.02 x 10 23 particles (atoms or molecules) – depending on what you are looking at. A mole of anything contains the same number of “things” as a mole of anything else. one mole is set by defining one mole of carbon 12 atoms to have a mass of exactly 12 grams.

Create a Mole “Quantity” Poster Poster states: “A mole of contains 6.02 x 10 23.” Surrounding that statement is a bunch of pictures depicting your object. On the back it also states:  “The weight of 1 mole depends on the object”  “If it were a gas, 1 mole would occupy 22.4 liters” Grade based on completeness, creativity, effort, and overall effect.

“Definition” of the molar mass: Molar Mass = Mass of 1 mole Weight, in GRAMS, is numerically equal to what its “atomic” weight was in a.m.u.’s What is the molar mass of Water (H 2 O)? 18.0 a.m.u.’s 18.0 grams / mole What is the molar mass of CO 2 ? 44.0 grams / mole

Use Molar Mass Use 22.4 L Use 6.02 x 10 23

Practice Problem: How many moles are in 5.0 g of copper? 1 mole Cu = 63.5 g 5.0 g of Cu Should we have more or less than 1 mole? 5.0 g Cu x 1 mole Cu = 63.5 g Cu.079 moles Cu 5.0g Cu = 63.5 g/mol

How many moles are in 26.0 g of NH 3 ? 1 mole NH 3 = 14.0 + 3.0 = 17.0 g More or less than 1 mole? 26.0 g NH 3 / 17.0 g/mol = 1.53 moles NH 3

Going the other direction: How many grams are in 1.5 moles of H 2 O? 1 mole H 2 O = 18.0 g 1.5 mol H 2 O x 18.0g H 2 O = 1 mol H 2 O 1.5 mol H 2 O x 18.0 g/mol = 27 g H 2 O

Use Molar Mass Use 22.4 L Use 6.02 x 10 23

Volume of a Mole of Gas The volume of gas varies with temperature and pressure At Standard temperature and pressure (STP), a mole of ANY gas occupies 22.4L (molar volume) Standard Temp. = 0 o C Standard Pressure = 101.3 kpa

Practice Problem: Sulfur Dioxide (SO 2 ) is a gas produced by burning coal. It is a pollutant that causes acid rain. Determine the volume, in liters, of 0.60 moles of SO 2 gas at STP. At STP, CO 2 occupies 36.5L. How many moles of CO 2 gas is in the sample?

Use Molar Mass Use 22.4 L Use 6.02 x 10 23

Scientific Notation Refresher: Multiplication:  Multiply Coefficients  Add Exponents Division:  Divide Coefficients  Subtract Exponents

Practice Problems: How many molecules are in 1.5 moles of H 2 O? 9.03 x 10 23

Going the other direction: How many moles are in 1.806 x 10 24 atoms of Oxygen? 3 moles

Use Molar Mass Use 22.4 L Use 6.02 x 10 23

Tying it all TOGETHER: How many molecules are in 300g of Na 2 SO 4 ? How many grams are in 4.56 x 10 23 atoms of Gold (Au)? What volume, in Liters, would 40g of O 2 gas occupy at STP?

Percent Composition and Chemical Formulas

Percent Composition =  the percent by mass of each element in a compound. % mass of element = Mass of element Mass of compound x 100%

Percent Composition Calculate the formula mass of C 2 H 3 O 2 ? What percent of this compound is oxygen by mass? % mass of element = Mass of element Mass of compound x 100% 32.0g 59.0g x 100% = 54.2%

9.03 g Mg combine completely with 3.48 g N to form a compound. What is the percent composition of this compound? % Mg = mass of Mg x 100 = 9.03 g x 100 = 72.2% Mg mass of compound 12.51 g (9.03 g + 3.48 g = 12.51 g) % N = mass of N x 100 = 3.48 g x 100 = 27.8 % N mass of compound 12.51 g

Practice Problem: Propane, C 3 H 8, is commonly used in gas grills. Calculate the percent composition of this compound.

Calculating Empirical Formulas Empirical Formula = the lowest whole-number ratio of atoms of the elements in a compound. may or may not be the same as a molecular formula.

H 2 O 2 = molecular formula HO = empirical formula CO 2 = molecular formula CO 2 = empirical formula

Calculating Molecular Formulas: The molecular formula of a compound can be determined if you know its empirical formula and its molar mass.

Example: Calculate the molecular formula of the compound whose molar mass is 60.0 g and empirical formula is CH 4 N. First calculate the empirical formula mass. Then divide the empirical formula mass into the molar mass. Multiply formula subscripts by this value to get the molecular formula.