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Chemical Composition

Chemical Composition
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Dr.SamuelHunt,United Arab Emirates,Teacher
Published Date:21-07-2017
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Chapter 6 Chemical Composition www.ThesisScientist.comWhy Is Knowledge of Composition Important? • All matter is either chemically or physically combined into substances. • Knowing the fraction of material you have can tell you:  the amount of sodium in sodium chloride for diet.  the amount of iron in iron ore for steel production.  the amount of hydrogen in water for hydrogen fuel.  the amount of chlorine in freon to estimate ozone depletion. www.ThesisScientist.comHow much seed do you plant? • In a garden you count the seeds by hand. How many seeds would you know to plant in a field? www.ThesisScientist.comCounting by Weighing • Building a house requires a lot of nails. • If you know that a single nail weighs .0122 g, than 100 nails weigh 1.22 g, a 1000 nails weigh 12.2 g and so on. • Analogy: You want to make 100 lbs of Al O , how much aluminum do 2 3 you use www.ThesisScientist.comCounting Nails by the Pound, Continued A hardware store customer buys 2.60 pounds of nails. A dozen nails has a mass of 0.150 pounds. How many nails did the customer buy? 1 dozen nails = 0.150 lbs. 12 nails = 1 dozen nails Solution map: www.ThesisScientist.comCounting Nails by the Pound, Continued 1 doz. nails 12 nails 2.60 lbs. 208 nails 0.150 lbs. 1 doz. • The customer bought 2.60 lbs of nails and received 208 nails. He counted the nails by weighing them www.ThesisScientist.comCounting Nails by the Pound, Continued • What if he bought a different size nail? Would the mass of a dozen be 0.150 lbs? Would there still be 12 nails in a dozen? Would there be 208 nails in 2.60 lbs? How would this effect the conversion factors? www.ThesisScientist.comCounting Atoms by Moles • If we can find the mass of a particular number of atoms, we can use this information to convert the mass of an element sample to the number of atoms in the sample. 23 • The number of atoms we will use is 6.022 x 10 and we call this a mole. 23 1 mole = 6.022 x 10 things. Like 1 dozen = 12 things. Avogadro’s number. 100 Like a kilo = 1000 or a Google = 1×10 www.ThesisScientist.comChemical Packages—Moles • Mole = Number of carbon atoms ―in‖ 12 g of C-12. 1 mole protons or 1 mole of neutrons = 1 amu C-12 exactly 6 protons and 6 neutrons since 1 mole × 1 amu = 1 g. 1 mole of C-12 (which is 12 amu) weighs exactly 12 g. 23 • In 12 g of C-12 there are 6.022 x10 C-12 atoms. 23 1 mole 6.02210 atoms 23 1 mole 6.02210 atoms www.ThesisScientist.comExample 6.1: 22 • A silver ring contains 1.1 x 10 silver atoms. How many moles of silver are in the ring? www.ThesisScientist.comExample: A silver ring contains 1.1 22 x 10 silver atoms. How many moles of silver are in the ring? • Write down the given quantity and its units. 22 Given: 1.1 x 10 Ag atoms www.ThesisScientist.comInformation: Example: 22 Given: 1.1 x 10 Ag atoms A silver ring contains 1.1 22 x 10 silver atoms. How many moles of silver are in the ring? • Write down the quantity to find and/or its units. Find: ? moles www.ThesisScientist.comInformation: Example: 22 Given: 1.1 x 10 Ag atoms A silver ring contains 1.1 22 Find: ? moles x 10 silver atoms. How many moles of silver are in the ring? • Collect needed conversion factors: 23 1 mole Ag atoms = 6.022 x 10 Ag atoms. www.ThesisScientist.comInformation: Example: 22 Given: 1.1 x 10 Ag atoms A silver ring contains 1.1 Find: ? moles 22 x 10 silver atoms. How Conversion Factor: many moles of silver are 23 1 mole = 6.022 x 10 in the ring? • Write a solution map for converting the units: atoms Ag moles Ag 1 mole Ag 23 6.02210 Ag atoms www.ThesisScientist.comInformation: Example: 22 Given: 1.1 x 10 Ag atoms A silver ring contains 1.1 Find: ? moles 22 x 10 silver atoms. How Conversion Factor: many moles of silver are 23 1 mole = 6.022 x 10 in the ring? Solution Map: atoms  mole • Apply the solution map: 1 mole Ag 22 1.110 Ag atoms moles 23 6.02210 Ag atoms -2 = 1.8266 x 10 moles Ag • Significant figures and round: -2 = 1.8 x 10 moles Ag www.ThesisScientist.comInformation: Example: 22 Given: 1.1 x 10 Ag atoms A silver ring contains 1.1 Find: ? moles 22 x 10 silver atoms. How Conversion Factor: many moles of silver are 23 1 mole = 6.022 x 10 in the ring? Solution Map: atoms  mole • Check the solution: 22 -2 1.1 x 10 Ag atoms = 1.8 x 10 moles Ag The units of the answer, moles, are correct. The magnitude of the answer makes sense 22 since 1.1 x 10 is less than 1 mole. www.ThesisScientist.comPractice—Calculate the Number of Atoms in 2.45 Mol of Copper. www.ThesisScientist.comPractice—Calculate the Number of Atoms in 2.45 Mol of Copper, Continued. Given: 2.45 mol Cu Find: atoms Cu Solution Map: mol Cu atoms Cu 23 6.02210 atoms 1 mol 23 Relationships: 1 mol = 6.022 x 10 atoms 23 Solution: 6.02210 atoms 2.45 mol Cu 1 mol 24  1.4810 atoms Cu Check: Since atoms are small, the large number of atoms makes sense. www.ThesisScientist.comRelationship Between Moles and Mass • The mass of one mole of atoms is called the molar mass. • The molar mass of an element, in grams, is numerically equal to the element’s atomic mass, in amu. • The lighter the atom, the less a mole weighs. • The lighter the atom, the more atoms there are in 1 g. www.ThesisScientist.comMole and Mass Relationships Substance Pieces in 1 mole Weight of 1 mole 23 Hydrogen 6.022 x 10 atoms 1.008 g 23 Carbon 6.022 x 10 atoms 12.01 g 23 Oxygen 6.022 x 10 atoms 16.00 g 23 Sulfur 6.022 x 10 atoms 32.06 g 23 Calcium 6.022 x 10 atoms 40.08 g 23 Chlorine 6.022 x 10 atoms 35.45 g 23 Copper 6.022 x 10 atoms 63.55 g 1 mole 1 mole carbon sulfur 12.01 g 32.06 g www.ThesisScientist.com