Chapter 11

 1. Describe how a mole is used in chemistry.  2. Relate a mole to common counting units.  3. Convert the number of moles to the number of particles present, and number of particles to number of moles.

 Chemists need a way to accurately count the number of very small things, like atoms and molecules.  The word “mole” just means a certain quantity.  Like ‘dozen’ means 12, be it eggs or bowling balls.

 Abbreviated: mol  Defined by the number of carbon atoms in 12 grams of carbon-12.  A mole of anything has this many particles: 6.02 x 10 23

 This number is called “Avagadro’s Number”.  Expanded, it looks like this: It’s such a big number, because it counts such small things.

 One mole of water (H 2 O)  One mole of sodium chloride (NaCl)  These are obviously not the same mass – but there are the same number of molecules in each sample.

 Conversion factor: 6.02 x / 1 mole # of moles x 6.02x mole  So how many atoms in 2.5 moles of Zn?  How many molecules of H 2 O in 11.5 moles?  How many molecules sucrose in 3.5 moles?

 Conversion factor: 1 mole / 6.02 x # of particles x 1 mole 6.02x10 23 atoms  How many moles in each of the following? 5.75 x atoms Al3.58 x units Zn Cl x molecules CO x atoms Fe

 How is a mole like a dozen, or a pair?  What is the relationship between Avagadro’s number and the mole?  How would you convert the number of particles to number of moles?  Why do we use the mole?

 Do you think that one dozen eggs have the same mass as one dozen lemons?  They only have the same number of items, not the same mass.  Same goes for elements and compounds…

 Molar Mass: mass (in grams) of one mole of any substance.  It is numerically equal to the average atomic mass on the periodic table.  What is the molar mass of nitrogen? Potassium? Aluminum?  How many particles in one mole of nitrogen? Potassium? Aluminum?

 Suppose, for a lab, you need 3.0 moles of Manganese. Using a balance, how many grams of Manganese would you measure out? [Molar Mass of Mn] x 3.0 moles 54.9 x 3.0 moles= 165g Mn

(# moles) x # of grams = mass 1 mole  What is the mass of the following? 3.57 mol Al3.45 mol Co 42.6 mol Si2.45 mol Zn

 You can also convert from mass to number of atoms, or atoms to mass.  How many atoms of gold are present in a 25.0g nugget of gold?  First, convert mass to moles.  Second, convert moles to number of atoms.

 1. Mass to moles: 25.0g x (1 mol/196.97g) = mol  2. Moles to atoms: mol x (6.02x10 23 atoms/1 mol) = 7.65 x atoms Ag

 How many atoms in the following? 55.2 g Li0.230 g Pb  What is the mass (in grams) of the following? 1.00 x atoms Mn1.5 x atoms N

 Notice that the mole is always at the center of the calculation. MassMoleParticles 1 mole Number of grams 1 mole 6.02x10 23 particles 1 mol 6.02x10 23 particles

 Explain what is meant by molar mass.  What conversion factor is used to convert mass to moles? Moles to mass?  What are the steps needed to convert mass to the number of atoms?

 Remember that a chemical formula shows us the number and types of atoms in a compound.  CCl 2 F 2 has 1 Carbon atom, 2 Chlorine atoms, and 2 Fluorine atoms.  To find the molar mass of a compound, we simply add the individual masses together.

 CCl 2 F 2  Mass of Carbon = 12.0 g  Mass of Chlorine = 35.4 g  Mass of Fluorine = 19 g  Molar Mass of CCl 2 F 2 = 12 + (2) (2)19 = g

 What is the mass of 1 mole of H 2 O?  What is the mass of 1 mole of sucrose (C 6 H 12 O 6 )?