Document Sample

Introduction to the Mole and Molar Mass Background • When you buy eggs you usually Dozen ask for a _______ eggs. • You know that one dozen of any 12 item is ______. Paper • Paper is packaged by a ream. • A ream of paper has 500 sheets. • Why is it useful to use units like a dozen or a ream? • Scientists had to select a bigger unit for counting molecules of substances. • The unit scientists use is called a MOLE. A mole can be thought of as a chemist's dozen One MOLE of anything has 602,200,000,000,000,000,000,000 items. AVOGADRO’S NUMBER Symbol = NA •6.02 x 1023 • One MOLE of anything has 6.02 x 10 23 items. How many Hershey’s Kisses make up 1 23 MOLE? 6.02 x 10 How many caramels make up 10 MOLES? 10 x [6.02 x 10 23] 60.2 x 1023 Or 6.02 x 1024 Find the number of Jolly Ranchers in 4 MOLES. 4 [6.022 x 1023] 24.088 x 10 23 2.41 x 10 24 How many moles are 6.022 x 1023 atoms of 1 sodium? _____ How many moles are 12.04 x 1023 atoms of carbon? _____ 2 12.04 x 1023 = 2 6.022 x 1023 How many moles are 18.06 x 1023 atoms of sodium? _____ 3 18.06 x 1023 = 3 6.022 x 1023 How many moles are 60.22 x 1023 atoms of sodium? _____ 10 60.22 x 1023 = 10 6.022 x 1023 How many moles are 6.022 x 10 23 molecules of water? _____ 1 How many moles are 12.04 x 10 23 molecules 2 of water? _____ 12.04 x 1023 = 2 6.022 x 1023 How many moles are 30.10 x 10 23 molecules of water? _____ 5 30.10 x 1023 = 5 6.022 x 1023 Part 2 Molar Mass • Scientists use the Periodic Table to determine the mass of a mole of atom of an element. • For example, a mole of Iron (Fe) atoms would have a mass of 55.85g. Periodic Table The mass of 1 mole of Strontium (Sr) is ___ g. 87.62 38 Sr 87.62 The mass of 1 mole of Lead (Pb) is ____ g. 207.2 82 Pb 207.2 66. The mass of 1 mole of Nickel (Ni) is ____ g. 58.69 28 Ni 58.69 The mass of 4 moles of Strontium (Sr) is _____g. 350.48 38 Sr 87.62 The mass of 0.5 moles of Lead (Pb) is ____ g. 103.6 82 Pb 207.2 The mass of 100 moles of (Ni) is _____ g. 5869.00 28 Ni 58.69 Molar Mass • Scientists also use the Periodic Table to determine the molar mass (formula weight) of compounds. • The molar mass of the compound is the sum of the molar masses of the elements that make up the compound. Potassium Chloride • The molar mass of Potassium Chloride is: Potassium (K) 39.10 g/mole Chloride (Cl) +34.45 g/mole 73.55 g/mole Potassium Permanganate • The molar mass of KMnO4 is the sum of all the molar masses times the number of atoms of each element for the molecule (subscript). Potassium Permanganate KMnO4 • Potassium (K) 39.10 g/mole • Manganese (Mn) 54.94g/mole • Oxygen (O) 4[16.00 g/mole] 158.04 g/mole. The molar mass of 1 mole of Sodium Chloride (NaCl) is____ g. 58.44 The molar mass of 1 mole of Lead Iodide (PbI2) is _____ g. 461.0 The mass of 100 moles of Nickel Sulfide (NiS) 9076.00 is ________ g. The mass of 1 mole of s Glucose (C6H12O6) is ______ g. 180.156 The mass of 1 mole of is Sucrose (C12H24O12 ) _______ g. 306.31 The mass of 4 moles of Glucose (C6H12 O6) is _________ g. 720.624 Mole Conversions • In chemistry, the mole is the standard measurement of amount. • However, balances DO NOT give readings in moles. Balances give readings in grams. • So the problem is that, while we compare amounts of one substance to another using moles, we must also use grams, since this is the information we get from balances. There are three steps to converting grams of a substance to moles. 1. Determine how many grams are given in the problem. 2. Calculate the molar mass of the substance. 3. Divide step one by step two. The three steps above can be expressed in the following proportion: Grams Moles --------------- = -------------- Molar Mass 1 Mole Example #1 - Convert 25.0 grams of KMnO4 to moles. Step One: The problem will tell you how many grams are present. Look for the unit of grams. The problem gives us 25.0 grams. Step Two: You need to know the molar mass of the substance. The molar mass of KMnO4 is 158.034 grams/mole. Potassium (K) = 39.10 x 1 = 39.10 g Manganese (Mn) = 54.94 x 1 = 54.94 g Oxygen (O) = 16.00 x 4 = 64.00 g --------------- 158.04 g Step Three: You divide the grams given by the substance's molar mass (25.0/158.04) The answer of 0.16 mole has been rounded off. Example #2 - Calculate how many moles are in 57.0 grams of Mg(NO3)2 Step One: 57.0 grams are given in the text of the problem. Step Two: The molar mass is 148 grams/mole. Mg (Magnesium) = 24 x 1 = 24 g N (Nitrogen) = 14 x 2 = 28 g O (Oxygen) = 16 x 6 = 96 g Step Three: Again you divide the grams by the substances molar mass (57.0 g/148 g). This answer has been rounded to 0.39 moles. Practice Problems 1. Calculate the moles present in: 2.00 grams of H2O 0.11 moles water 2. Calculate the moles present in: 75.57 grams of KBr 0.635 moles KBr 3. Calculate the moles present in: 100.0 grams of KClO4 0.72 moles KClO4 4. Calculate the moles present in: 225.5 grams of Sucrose (C12H24O12) 0.63 moles Sucrose 5. Calculate the moles present in: 350.0 grams of Glucose (C6H12O6) 1.943 moles Glucose Homework 1. Calculate the moles present in: 3.00 grams of NaCl .05 moles 2. Calculate the moles present in: 25.0 grams of NH3 1.47 moles NH3 3. Calculate the moles present in: 16.0 grams of KCl .21 moles KCl 4. Calculate the moles present in: 30.25 grams of BeCl2 .38 moles KCl 5. Calculate the moles present in: 175.25 grams of Li2S 3.81 moles Li2S 6. Calculate the moles present in: 75.62 grams of CO2 1.72 moles CO2 7. Calculate the moles present in: 56.5 grams of H2O 3.14 moles H2O 8. Calculate the moles present in: 22.6 grams of CH3COOH .38 moles CH3COOH 9. Calculate the moles present in: 18.4 grams of AgCl .13 moles AgCl 10. Calculate the moles present in: 68.3 grams of HCN 2.53 moles HCN

DOCUMENT INFO

Shared By:

Categories:

Tags:

Stats:

views: | 89 |

posted: | 8/17/2012 |

language: | simple |

pages: | 57 |

OTHER DOCS BY cuiliqing

How are you planning on using Docstoc?
BUSINESS
PERSONAL

By registering with docstoc.com you agree to our
privacy policy and
terms of service, and to receive content and offer notifications.

Docstoc is the premier online destination to start and grow small businesses. It hosts the best quality and widest selection of professional documents (over 20 million) and resources including expert videos, articles and productivity tools to make every small business better.

Search or Browse for any specific document or resource you need for your business. Or explore our curated resources for Starting a Business, Growing a Business or for Professional Development.

Feel free to Contact Us with any questions you might have.