Chapter 6. Chemical Composition

Transcription

1 Chapter 6 Chemical Composition

2 Formula Mass The mass of an individual molecule or formula unit Also known as molecular mass or molecular weight Sum of the masses of the atoms in a single molecule or formula unit mass of 1 molecule of H2O = 2(1.01 amu/h atom) + 1(16.00 amu/o atom) = amu mass of 1 formula unit of MgCl2 = 2(35.45 amu/cl atom) + 1(24.30 amu/mg atom) = amu

3 Sample Calculations of Formula Mass Mass a. Na2HPO4 Na2 2 x = H 1 x = P 1 x = O4 4 x = amu/formula unit b. Ca3(PO4)2 Ca3 3 x = (P )2 2 x = ( O4)2 8 x = amu/formula unit c. C15H22ClNO2 C15 15 x = (Demerol) H22 22 x = Cl 1 x = N 1 x = O2 2 x = amu/molecule

4 Counting by Weighing: Nails by the Pound Some hardware stores sell nails by the pound, which is easier than selling them by the nail. Customers often need hundreds of nails and counting them takes too long. A customer still needs to know the number of nails contained in a given weight of nails.

5 A hardware store customer buys 2.60 lb of medium-sized nails, where a dozen of these nails weigh lb. How many nails did the customer buy? 1 lb nails doz nails number of nails 1 doz nails = lb nails 1 doz nails = 12 nails 1 doz nails lb nails lb nails 1 doz nails 12 nails 1 doz nails 1 doz nails 12 nails 1 doz nails 12 nails 2.60 lb nails x x = nails lb nails 1 doz nails 208

6 1 doz nails = lb nails

7 Moles and Calculations with Moles

8 What is an amu? Moles 1.66 x g (~ the mass of a proton) We need a conversion to the macroscopic world. How many hydrogen atoms are in 1.00 g of hydrogen? 1 H atom 1.00 g H x = 6.02 x H atoms 1.66 x g H Avogadro s Number

9 Moles Consider carbon-12 (the most abundant isotope of C) What is the mass of one carbon-12 atom? amu g g 12 x 1.66 x = 1.99 x C atom amu C atom What is the mass of Avogadro s number of C atoms? g 6.02 x C atoms x 1.99 x = g C atom

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11 Definition of a mole A mole is the amount of any substance that contains as many elementary entities as there are atoms in exactly 1.00 g of hydrogen-1. A mole is the amount.. in exactly g of carbon x of anything It is important to state the entities involved: atoms, formula units, molecules, ions, electrons

12 How Large a Quantity is Avogadro s Number??

13 How can we use Avogadro s Number?? objects moles 6.02 x 1023 objects mole 1 mole x 1023 objects

14 1. How many atoms are represented by 3.00 moles of calcium (Ca)? 6.02 x mol Ca x 23 Ca atoms = x x Ca atoms 1.00 mol Ca 2. How many moles are represented by 1.0 x 10 6 molecules of carbon monoxide (CO)? 1.0 x 10 6 molecules CO x 1.00 mol CO 6.02 x molecules CO = x 10x mol -18 mol CO CO

15 Definition of a molar mass (g/mol) Molar mass of an element The mass in grams that is numerically equal to the atomic weight of the element.

16 Molar mass of an element

17 Definition of a molar mass (g/mol) Molar mass of a molecular form of an element N2, g/mol Cl2, g/mol (O2, I2, F2, Br2)

18 Definition of a molar mass (g/mol) Molar mass of a compound The mass in grams that is numerically equal to the formula weight of the compound. (The sum of the atomic weights involved) H2O, g/mol ( ) BaCl2, g/mol ( ) CO2, g/mol ( )

19 What can we use molar mass for? grams of an element moles of an element mol C g C g C mol C

20 3. Calculate the moles of carbon in g of carbon. g C mol C g C 1 mol C 1 mol C = g C conversion factors 1 mol C g C 1 mol C g C x = 2.21 x 10-3 mol C g C

21 1.000 mol CO g CO g CO mol CO2 grams of an element moles of an element mol C g C g C mol C Molar mass grams of a compound moles of a compound

22 4. How many grams are contained in 4.25 moles of carbon dioxide (CO2)? mol CO2 g CO2 1 mol CO2 = g CO g CO2 1 mol CO2 conversion factors 1 mol CO g CO g CO mol CO2 x = 187 g CO2 1 mol CO2

23 g of CO2 is equal to how many moles of CO2? g CO2 mol CO2 1 mol CO2 = g CO g CO2 1 mol CO2 conversion factors 1 mol CO g CO2 1 mol CO g CO2 x = mol CO g CO2

24 grams of an element moles of an element # atoms of an element grams of a compound moles of a compound # molecules of a compound grams of a compound moles of a compound # formula units of compound? Molar Mass? Avogadro s #

25 The Big Picture of Moles grams of something moles of something particles of something? Molar Mass? Avogadro s #

26 6. How many copper atoms are in a 3.10 g of copper? g Cu mol Cu atoms Cu 1 mol Cu = g Cu 1 mol Cu = x Cu atoms g Cu 1 mol Cu 1 mol Cu g Cu conversion factors 1 mol Cu x Cu atoms x Cu atoms 1 mol Cu 3.10 g Cu x 1 mol Cu x x Cu atoms = 2.94 x Cu atoms g Cu 1 mol Cu

27 7. What is the mass of 1.77 x molecules of CO2? molecules of CO2 mol CO2 grams CO2 1 mol CO2 = x CO2 molecules 1 mol CO2 = g CO2 1 mol CO x CO2 molecules x CO2 molecules 1 mol CO2 conversion factors g CO2 1 mol CO2 1 mol CO g CO x CO2 molecules x 1 mol CO x CO2 molecules x g CO2 = 1.29 x 10 8 g CO2 1 mol CO2

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29 Chemical Formulas as Conversion Factors How many leaves on 14 clovers? clovers leaves 3 leaves 1 clover 1 clover 3 leaves 14 clovers x = 42 leaves 3 leaves 1 clover

30 Converting Between Moles of a Compound and Moles of a Constituent Element: moles of compound moles of element in compound? Chemical Formula

31 8. Find the number of moles of O in 1.7 mol CaCO3. mol CaCO3 O 1 mol CaCO3 = 3 mol O 3 mol O 1.7 mol CaCO3 x 1 mol = 5.1 mol O CaCO3

32 Converting Between Grams of a Compound and Grams of a Constituent Element 9. Find the mass of sodium in 15 g of NaCl. g NaCl mol NaCl mol Na g Na molar mass formula molar mass 1 mol NaCl 1 mol Na g Na 15 g NaCl x x x = 5.9 g Na g NaCl 1 mol NaCl 1 mol Na