The Mole Chapter 11

Counting large numbers… Easier when you use counting units: Dozen Ream Pair Case Gross Regardless of the object, the number that the units represents is always the same

Atoms and molecules are extremely small Impossible to actually count them (even in the smallest of samples) Chemists need a unit for counting accurately the # of atoms, molecules, or formula units They use the mole Mole (mol) = the SI base unit used to measure the amount of a substance 1 mole of anything contains 6.02 x 1023 representative particles

1 mole of apples = 6.02 x 1023 apples 1 mole of diamonds = 6.02 x 1023 diamonds 1 mole of baseballs = 6.02 x 1023 baseballs 1 mole of carbon atoms = 6.02 x 1023 carbon atoms

The same applies to moles of compounds How many molecules are in 1 mol NH3? 6.02 x 1023 NH3 molecules How many molecules are in 1 mol C9H8O4? 6.02 x 1023 C9H8O4 molecules

Amedeo Avogadro determined the volume of one mole of gas in 1811 6.02 x 1023 Known as Avogadro’s number Where did it come from? Amedeo Avogadro determined the volume of one mole of gas in 1811

Converting Moles to Particles and Particles to Moles How many roses are in 3 ½ dozen? USE CONVERSION FACTORS!!! 3.5 dozen x 12 roses = 1 dozen 42 roses How many pencils are in 6 gross? 6 gross x 144 pencils = 1 gross 864 pencils

Converting Moles to Particles and Particles to Moles How many particles of sucrose are in 3.50 moles of sucrose? 3.50 mol sucrose x 6.02 x 1023 rep. part. 1mol 2.11 x 1024 particles of sucrose

Converting Moles to Particles and Particles to Moles How many moles contain 4.50 x 1024 atoms of zinc? 4.50 x 1024 atoms Zn x 1 mol zinc 6.02 x 1023 atoms Zn 7.48 mol Zn

Try some on your own… How many Cu atoms are in 1.20mol Cu? 7.22 x 1023 Cu atoms How many moles of Xe contain 1.54 x 1026 atoms of Xe? 2.56 x 102 mol Xe

Mass and the Mole Mass of dozen limes = Mass of dozen eggs Moles of substances have different masses, due to the differing sizes and compositions 1 mol of C vs. 1 mol of Cu Molar mass= the mass in grams of one mole of any pure substance

The molar mass of any element is numerically equal to its atomic mass and has the units g/mol Ex: one atom of Manganese = 54.94amu molar mass of Manganese = 54.94g/mol So, when you measure out 54.94 g of manganese on a balance you are actually measuring out 6.02 x 1023 atoms of manganese Look at figure 11-4 in your textbook

Using Molar Mass Jellybean example Jelly beans sold by the dozen 1 doz jelly beans = 35 g If a customer wants 8 dozen jelly beans, should you count out 96 individual jelly beans or could you USE A CONVERSION FACTOR?

Yep…you guessed it…use a conversion factor!! You could figure out the mass of 8 dozen jelly beans and measure the mass 8 doz jelly beans x 35 g jelly beans 1doz jelly beans = 280 g of jelly beans

Try one on your own… A customer comes into your candy store and wants 16 doz jelly beans, use a conversion factor to figure out how many grams you should measure out. 16 doz x 35 g 1 doz = 560 g jelly beans

Apply it to working in a chemistry lab… You are a lab assistant and want 0.0450mol of chromium. Using a conversion factor, calculate the mass in grams of 0.0450mol of chromium. Molar mass of chromium = 52.00g/mol 0.0450mol x 52.00g 1 mol = 2.34 g Cr You would need to measure out 2.34 g of Chromium

Try one on your own… You need 3.0 moles of Mn for a chemical reaction. Calculate how many grams of Mn you would need to measure out. 3.0mol x 54.9g 1mol = 165g Mn

You know how to convert moles to mass, let’s try converting mass to moles!! Use the inverse of the conversion factor!! Let’s say you have 200g of Mn. How many moles do you have? 200g x 1mol 54.9g = 3.64mol Mn

Let’s do some more converting!!

Your boss is so impressed with your skills that he gives you a raise!! Mass to atoms You are back at the candy store and at the end of the day you have 910g of jelly beans left. Your boss wants to know how many jellybeans this is. Rather that count out the individual candies, you decide to use your superior brain power and calculate it mathematically!! 910g x 1 doz 35g = 26 doz jelly beans left Your boss is so impressed with your skills that he gives you a raise!!

How many atoms of gold are in a pure gold nugget with a mass of 25.0g? Now try it with atoms… How many atoms of gold are in a pure gold nugget with a mass of 25.0g? You can’t go directly from mass to atoms, so you have to convert to moles first 25.0g x 1mol 196.7g = 0.127 mol Au 0.127mol x 6.02 x 1023 atoms 1mol = 7.65 x 1022 atoms of Au

Chemical Equations Coefficients in a chemical equation represent the numbers of individual particles of substances in the equation …they also represent the numbers of moles of particles C3H8 + 5O2  3CO2 + 4H2O

Mole Ratios Mole ratio = ratio between the numbers of moles of any two substances in a balanced chemical equation C3H8 + 5O2  3CO2 + 4H2O

2Al + 3Br2  2AlBr3 What mole ratios can be written for this reaction? 2mol Al 4. 3mol Br2 3molBr2 2mol AlBr2 2mol Al 5. 2molAlBr3 2molAlBr3 2Al 3mol Br2 6. 2molAlBr3 2mol Al 3molBr2

Chemistry Matter and Change Courtesy of Chemistry Matter and Change Glencoe McGraw-Hill Chemistry for Dummies John T. Moore www.karentimberlake.com