Unit 5 The Mole

Molecular and Formula Mass Atomic mass unit (u) = the unit of mass for atoms Molecular mass is the sum of the masses of all atoms in a molecule Formula mass is the sum of the masses of all atoms in a formula unit of an ionic compound

Examples Molecular mass of H2O is Formula mass of Ca(NO3)2 is 18 u 1 Ca atom = 1 x 40.1 2 N atoms = 2 x 14.0 6 O atoms = 6 x 16.0 Sum is 161.4 u

Assignment Complete: Exercises 1-2 page 80 10 points Due next class

Avogadro’s Number 6.02 x 1023 Avogadro’s number is equal to 1 mole Makes working with large numbers easier Instead of saying you have 12,000,000,000,000,000,000,000,000 molecules of NH3, you can say you have 19.9 moles of NH3

6.02 x 1023 = 1 mole How big is a mole? If there were 1 mole of people, it would take 120 trillion Earths to accommodate them! 6.02 x 1023 = 1 mole

The Mole 1 mole = 6.02 x 1023 of anything 1 mole of atoms is _______ atoms 1 mole of baseballs is ______ baseballs 1 mole of dimes is ______ dimes Molar mass is the mass of one mole of molecules, atoms, ions, or formula units

Conversions Use the factor label method Grams to moles Moles to grams Take the amount in grams and divide by the molar mass of that compound Moles to grams Moles multiplied by the molar mass Molecules to moles Divide the number of molecules by 6.02 x 1023 These conversions can also be combined

Conversions

Assignment Complete: Problems 3-8 page 83 10 points Due tomorrow

Moles and Gases One mole of any gas is 22.4 Liters One mole of oxygen gas = ______ L One mole of CO2 gas = ________ L One mole of Neon gas = _______ L

The Mole Song A mole is an animal that burrows in the ground,Or a spot on your chin that you gotta shave around.But there's another kind of mole of interest to me,That's the kind of mole they use in chemistry.  Chorus: A mole is a unit, or have you heard, Containing six times ten to the twenty-third, That's a six with twenty-three zeros at the end, Much too big a number to comprehend.

Mole song Say you had a mole of pennies to distribute 'round the world,Give to each of the five billion grownups, boys, and girls,There wouldn't be a single soul down and out of luck,Cause everybody in the world would get a trillion bucks.  Or say you had a mole of paper and stacked it toward the sky,Paper's awful thin, but that pile would get so high,It'd reach up into outer space, in fact I think you'd find,It'd go up to the moon and back, eighty billion times.  Chorus

Mole song Suppose a mole of marshmallows fell upon the planet,Over each square inch of land and sea, think that you could stand it?That layer would be twelve miles high and of course block out the sun,We're talking close to five million trillion tons.  Well, maybe we could save ourselves if we all started eatin',One marshmallow each second, not two 'cause that'd be cheatin'.With five billion people munching, how long do you think it'd take?Forty million years--and that's without a bathroom break.  Chorus

Mole song But say you had a mole of atoms, would the pile be immense,Should I say the answer now, or leave you in suspense?Well, atoms are so very, very small, you understand,You could hold a mole of atoms in the palm of your hand.  So shake a little sugar in the middle of your palm,Now you don't want to spill it, so try and stay calm.You hardly can imaging and barely realize,There's more atoms in that sugar than stars up in the sky.  Chorus

Moles in Solution Molarity (M) is the ratio between the moles of dissolved substance and the volume of solution M = mol of solute/dm3 of solution

Molarity calculations What is the molarity of 2.5 x 102 cm3 of solution containing 9.46 g CsBr M = mol solute/dm3 solution Convert g to moles 9.46g/213 g = 0.0444 mol CsBr Convert cm3 to dm3 2.50 x 102 cm2/1000 = 0.250 dm3 Solve 0.0444 mol/0.250 dm3 = 0.178 M CsBr

Molarity calculations cont… Those three steps can be combined into one continuous chain 9.46 g 1 mol 1000 cm3= 2.50 x 102 cm3 213 g 1 dm3 = 0.178 M CsBr

Making a solution How would you prepare 5.0 x 102 cm3 of a 0.133 M solution of MnSeO4? 5.0 x 102 cm3 1 dm3 0.133 mol 198 g = 1000 cm3 1 dm3 1 mol = 13.2 g So, you would need to dissolve 13.2 g MnSeO4 in enough water to make 5.0 x 102 cm3 of solution

Assignment Complete: Problems 9-16 on page 85 Due by end of class

Percent composition The percentage composition of a compound is a statement of the relative mass each element contributes to the mass of a compound as a whole Calculations Find the mass of each element Divide each by the formula mass Multiply each by 100 to get a percentage

Empirical Formulas The empirical formula is the simplest ratio of atoms in a compound H2O2  HO Calculations Determine the moles of each element in the compound Divide the number of moles by the smallest one to get a ratio

Empirical Formula from Percentage Composition Example – see page 88 Change % to grams Change g to moles Find ratio

Assignment Complete: 17-22 page 86-87 23-26 page 89 10 points Due tomorrow

Molecular Formulas A molecular formula shows the actual number of atoms of each element in a molecule Problems The molecular mass of benzene is 78.0 u and its empirical formula is CH. What is its molecular formula? Molecular mass/empirical mass 78.0/13 = 6 C6H6

Hydrates Hydrates are crystals that contain water molecules NiSO3•6H20 means the one molecule of NiSO3 is being adhered to by 6 molecules of water Hydrate calculations

Assignment Complete: 27-31 page 90 and 32-35 page 92 10 points Due tomorrow

Chapter Review Complete practice exam