The Mole Beware the Mole!! General Chemistry

Chemical Measurements Everyday people perform jobs that require the ability to count and measure Chef- essential to measure ingredients correctly Construction worker- measuring cement, sand, gravel, and water determines the consistency of concrete Painter- adding the right mixture of colors creates new colors. With the mole, you’re doing the same math needed to convert $23 to cents, or pounds to tons, or centimeters to inches. It’s all called dimensional analysis.

Chemical Measurements Dozen = 12 Baker’s dozen = 13 Gross= 144 Mole (mol) = 6.02x1023 A mole of water molecules has a volume of only 18 mL! Molecules are unbelievably small, so a lot of them doesn’t take up that much space. The mole is useful in chemistry because it links the microscopic world of atoms, molecules, and ions, to the macroscopic world Can you imagine a mole of donuts?

Avogadro’s Number 6.02x1023 is so important in chemistry it’s given its own name… You guessed it, Avogadro’s Number In numerical form it looks like this: 602,000,000,000,000,000,000,000 A mole of paper would reach passed Pluto A mole of basketballs is the size of Earth A mole of rice would cover the land masses of Earth to a depth of 75 meters!

Scientific Notation Practice Using the mole requires that we are comfortable using scientific notation Write the following in scientific notation Write the following in standard notation 6000 0.0067 78,000,000 698,700 0.000009 0.0090076 6.00x103 6.70x10-3 7.80x107 6.99x105 9.00x10-6 9.01x10-3 6.02x104 9.03x109 7.77x10-2 9.21x10-7 60,200 9,030,000,000 0.0777 0.000000921

The mole The mole establishes a relationship between the atomic mass and the gram The mass in grams of 1 mole of a substance is equal to its atomic mass 6.02x1023 atoms Cu = 63.5 g = 1 mol Cu 6.02x1023 atoms H = 1.001 g = 1 mol H 6.02x1023 atoms Fe = 55.8 g = 1 mol Fe

What’s in a Mole? A mole of particles in an element is usually talking about atoms. The number of molecules in a mole of any molecular compound is 6.02x1023

Molar Mass The mass in grams of 1 mole of a substance is called the molar mass of the substance. The molar mass of an element is equal to its atomic mass. The unit for molar mass is grams per mole, or g/mol

Molar Mass Ne = 20.18 g/mol O2 = 16.00*2 = 32.00 g/mol U = 238.03 g/mol NaOH = 22.99 + 16.00 + 1.008 = 40.00 g/mol CO2 = 12.01 + 16.00*2 = 44.01 g/mol Al2(CO3)3 = 26.98*2 + (12.01*3) + (16.00*9) = 233.99 g/mol

Moles to Grams Conversions If you know the mass of a substance, you can calculate the number of moles. You have 11.2 g of NaCl. How many moles is that? 1. determine the molar mass of NaCl (using the periodic table) Na= 23.0 g/mol Cl= 35.5 g/mol 23.0 g/mol + 35.5 g/mol = 58.5 g/mol (get these #’s from the periodic table)

Unit Analysis Method Write down units asked for in answer to the right Write down the given value over 1 on the left Apply one or more unit factors to cancel units It’s as easy as 1-2-3!

Moles to Grams Conversions Molar mass of NaCl = 58.5 g/mol Set up a conversion factor (a fraction whose value is equal to 1) The units we need should be in the numerator and the units you already know in the denominator.

Moles to Grams Conversions You can also determine the mass of a sample if you know the number of moles 2.50 mol of NaCl is how many grams? Set up a conversion factor 

Moles to Grams Conversions MASS How many moles are in 14 g LiOH? How many moles are in 15 g N2? g x mol = moles g Molar Mass moles x g = g mol MOLES 14 g LiOH 1 1 mol LiOH 23.95 g LiOH 0.58 mol LiOH 15 g N2 1 1 mol N2 28.02 g N2 0.54 mol N2

Moles to Grams Conversions How many grams are in 4 mol H2O2? How many grams are in 56 mol CaCO3? 4 mol H2O2 1 34.016 g H2O2 1 mol H2O2 136.06 g H2O2 56 mol CaCO3 1 100.09 g CaCO3 1 mol CaCO3 5605.04 g CaCO3

Moles to Molecules Molecules OR atoms The number of particles in 1 mole of any substance is always the same- Avogadro’s number. or How many atoms are in 3 mol of elemental Ne? 6.02x1023 particles 1 mol 1 mol 6.02x1023 particles 3 mol Ne 1 6.02x1023 atoms 1 mol 1.81x1024 atoms Ne

Moles to Molecules (cont.) PARTICLES How many atoms of oxygen are in 6 mol of O2 molecules? How many moles of I2are in 8.02x1020 molecules of I2? Atoms Molecules? Use the subscript 6.02x1023 particles 1 mol Avogadro’s Number 1 mol 6.02x1023 particles MOLES 6 mol O2 1 6.02x1023 molecules O2 1 mol O2 2 atoms O 1 molec. O2 7.22x1024 atoms O 1 mol I2 6.02x1023 molecules I2 8.02x1020 molec. I2 1 1.33x10-3 mol I2

Multistep Conversions You want to impress your date by boasting you know how many molecules of table sugar are in the cake you just made. You need 250 g of sugar (C12H22O11). How many sucrose molecules will be in the cake? Plan: Convert the mass to moles using the molar mass and then convert to moles using Avogadro’s number. MASS PARTICLES Avogadro’s Number Use molar mass MOLES 250 g C12H22O11 1 1 mol C12H22O11 342.3 g C12H22O11 6.02x1023 molecules 1 mol C12H22O11 4.4x1023 molec. C12H22O11

Multistep Conversions If you burned 4.0x1024 molecules of methane (CH4) during a laboratory experiment, what mass of methane did you use? Plan: Convert your given # of molecules to moles using Avogadro’s number, then convert the moles to grams using the molar mass of methane. (12.00 + 1.004*4) 4.0 x 1024 molec. CH4 1 1 mol CH4 6.02x1023 molec. CH4 16.016 g CH4 1 mol CH4 106.42 g CH4