 # Chapter 7 Chemical Quantities. The Mole (Friend or foe)  What is a mole? 1. SI base unit to measure the amount of a substance 2. The amount of a substance.

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Chapter 7 Chemical Quantities

The Mole (Friend or foe)  What is a mole? 1. SI base unit to measure the amount of a substance 2. The amount of a substance that contains the same number of particles as the number of atoms in exactly 12 g of carbon-12

 What is Avogadro’s number? 1. the number of particles in a mole 2. 1 mole = 6.02 x 10 23 particles 3. particles are: atoms, ions, molecules, formula units

How do you use these numbers? 1. 1 mole of C = 6.02 x 10 23 atoms C 2. 1 mole of NaCl = 6.02 x 10 23 formula units NaCl 3. 1 mole of H 2 O = 6.02 x 10 23 molecules H 2 O 4. 1 mole of Ca +2 = 6.02 x 10 23 ions Ca +2

What is molar mass? 1. the mass in grams of one mole of a pure substance (element or compound) 2. use the periodic table to find the mass 3. What is the molar mass of helium? 4.0 g He mole 4. will be used as a conversion factor

5. Examples: a. What is the molar mass of 1 mole of Al? 27.0 g Al mole b. What is the molar mass of 1 mole of CO 2 ? C = (1)(12.0) = 12.0 O = (2)(16.0) = 32.0 44.0 g/mole

 Converting from moles to grams 1. What is the grams of 3.50 mole of Cu? 2. There are 11.9 g of Al, how many moles of Al are there?

3. How many moles are in 25.0 grams of H 3 PO 4 ?

Converting moles to molecules 1.How many molecules are in 5.2 moles of NaCl? 2.How many moles are in 3.12 x 10 15 Mg +2 ions?

Convert grams to molecules. 1.How many molecules are in 3.14 grams of NaOH? 2.How many grams are in 4.12 x 10 12 molecules of Rh? 3. How many molecules are in 523 g of KI?

 Percent Composition 1. Definition – the percent by mass of each element in the compound 2. Formula: % composition = mass of element 100 mass of compound

3. Ex. Find the percent composition of copper (I) sulfide. Cu 2 S Cu = 2(63.5) = 127.0 S = 1(32.1) = 32.1 159.1g/mole %Cu = 127.0 100 = 79.8% 159.1

%S =

 Empirical Formula 1.Shows the simplest whole-number ratio of the atoms in a compound 2. Examples: a.) C 2 H 8 = b.) Al 2 O 3 =

3. Examples: Analysis shows a compound to contain 26.56% K, 35.41% Cr, 38.03% O. Find the empirical formula.

 Molecular Formula 1. Indicates the ratio of the atoms 2. Indicates the actual number of atoms 3. n = Molecular mass empirical mass 4. (empirical formula) n = molecular formula

5. Examples: An organic compound is found to contains 92.25% C and 7.75% H. If the molecular mass is 78, what is the molecular formula?

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