Chemistry 11 INTRODUCTION TO UNIT TWO THE MOLE

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1 Chemistry 11 INTRODUCTION TO UNIT TWO THE MOLE What is a dozen? Consider: the mass of 12 donuts does not equal the mass of 12 timbits OR, consider: 150 g donuts vs. 150 g timbits. You will need a lot more timbits to reach this mass than donuts. Definition of the mole: the number of particles in exactly 12 g of the isotope Carbon -12. OR The number of carbon-12 atoms in 12 grams of unbound carbon in the ground state. That number is 6.02 x ( Avogadro's number ) Lorenzo Romano Amedeo Carlo Avogadro di Quaregna e di Cerreto 9 August 1776, Turin, 9 July 1856 For example: B 5 (atomic number 5) The mass of one Boron atom is 10.8 amu. atomic mass units This mass is compared to the Carbon-12 isotope. AMU is our standard to compare to! It is 1/12 of the C-12 atom. This is equivalent to 1.66 x kg x atoms of Boron are contained in 10.8 g of Boron. We say that the atomic mass is 10.8 g / mole. ( g / mole is a much more use-able unit to use than amu, especially when we have to do unit cancelling calculations) For example. The ionic compound, Calcium Sulphide. Chemical Formula CaS. 1 mole sulphur = 32.1 g That s 6.02 x sulphur atoms having a mass of 32.1g But we also say 1 sulphur atom = 32.1 amu 1 mole Ca = 40.1 g That s 6.02 x calcium atoms having a mass of 40.1g 1 Ca atom = 40.1 amu BUT, we can't work with amu, because this is only 1 molecule or compound or atom or element! Therefore it is more practical to talk about 1 mole of CaS molecules (or 6.02 x CaS molecules) = 72.1 g. So we would say that the molar mass of CaS is 72.1 g/mole. Also stated as molecular mass.

2 The Mole and History of The Term "Mole" Avogadro's number, the number of particles in a mole, can be experimentally determined by first "counting" the number of atoms in a smaller space and then scaling up to find the number of particles that would have a mass equal to the atomic or molecular mass in grams. The History of the Term"Mole" The Avogadro constant is named after the early nineteenth century Italian scientist Amedeo Avogadro, who is credited (1811) with being the first to realize that the volume of a gas (strictly, of an ideal gas) is proportional to the number of atoms or molecules. The French chemist Jean Baptiste Perrin in 1909 proposed naming the constant in honor of Avogadro. Real World Moles Given that the volume of a grain of sand is approximately m 3, and given that the area of the United States is about m 2, it therefore follows that a mole of sand grains would cover the United States in approximately one centimeter of sand. A human body contains very roughly one hundred trillion cells; there are roughly six billion people on Earth; so the total number of human cells on the planet is approximately * = , which is very close to one mole. Since the Earth has a radius of about 6400 km, its volume is approximately m 3. Since about 500 large grapefruit will fit in one cubic meter, it therefore follows that a mole of grapefruit would have approximately the same volume as the Earth. If you had a mole of pennies, you could give out enough money to everyone in the world so that they could spend a million dollars every hour, day and night, for the rest of their lives. ONE DOZEN can be: 12 dinner rolls 12 eggs 12 roses 12 blood cells (microscopic things too!) 12 of anything!!!!! Similarily, ONE MOLE Can be: x atoms x molecules x protons x ions x of anything!!!!

3 Check each of the following, to be sure that you understand how these molar masses were arrived at: SUBSTANCE Cu Sn H 2 O Copper sulphate MOLAR MASS 63.5 g / mole g / mole 18 g / mole 159 g / mole 1 mole Cu, 1 mole S, 4 moles O, but only 1 mole CuSO4!!! potassium chromate ammonium carbonite Chlorine gas Bromine liquid Phosphorus crystals Copper (I) phosphide 194 g / mole 96 g/ mole Cl 2!!! 71 g / mole Br 2!!! 1598 g / mole P 4!!! 124 g / mole 221 g/ mole (Not P 4 this time!)

4 COUNTING ATOMS Complete the following table. The first one is done for you. Molecular formula Name # of Molecules # of atoms 3 H 2 O water 3 6H 3O Ag 2 CO 3 Silver carbonate 1 2Ag 1C 3O 4 CuSO 4 Copper (II) nitrate 1 Ammonium sulphide 1 3 CaCl 2 2 H 2 O Calcium Chloride 3 Dihydrate chloride gas 1 Zinc acetate 1 Magnesium Phosphate 1 6 SnCl 2 5 H 2 O 7 LiH 2 PO 4 Aluminum Oxide Dihydrate 1

5 CONVERSION CALCULATIONS Complete the following. You MUST show all of your work in the conversions!!! Show your work on a separate piece of paper. 1) 540 Megabytes of ram = Gigabytes of ram 2) 18fg = Mg 3) 36 pencils = dozen 4) 5 pencils = dozen 5) 6.02 X pencils = moles 6) X pencils = moles 7) 41.0 g N = moles 8) 41.0 g N = atoms 9) The mass of 1 atom of nitrogen 10) X ammonia molecules = moles 11) The # of nitrogen atoms in #10: 12) The # of hydrogen atoms in #10: 13) The # of TOTAL atoms in #10: 14) 0.86 moles of ammonia = molecules

6 Starting to draw the mole map: PARTICLES MASS 6.02 x particles / mole g / mole (Avogadro's number) (molar mass) MOLE Sample calculations WHAT IS THE MASS in grams of one mole of lead? mass = 207 g mole WHAT IS THE MASS in grams of one atom of lead? mass = 207 g x 1 mole X 1 atom = mole 6.02 x atoms WHAT IS THE MASS in grams of 5.8 x atoms of lead? mass = 207 g x 1 mole X 5.8 x atoms = mole 6.02 x atoms 1

7 Mole Practice Worksheet #1 1. What is the atomic mass of a) rubidium b) astatine c) manganese 2. What is the molar mass of a) gallium manganate b) triiodine heptafluoride c) zinc carbonate 3. How many moles are there in a) 86 g of chlorine gas b) 258 g of tellurium dioxide gas c) g of carbon tetrafluoride gas 4. What is the mass in grams of a) 8 moles of ammonia b) 5.0 moles of nitric acid c) moles of hydrogen chloride 5. How many molecules/atoms are there in a) 4.5 moles of neon gas b) 1.50 moles of nitrogen dioxide gas c) 35.0 g of sulphur difluoride gas 6. What would be the mass in grams of a) 6.02 x atoms of osmium b) 1.53 x molecules of silicon tetrabromide c) 1 molecule of water Answers 1. atomic mass means the mass of a single atom a) 85.5 a.m.u. b) 210 a.m.u. c) 54.9 a.m.u. 2. molar mass means mass of 1 mole of the substance in grams a) 378 g/mole Ga(MnO 3 ) 3 b) 514 g/mole I 3 F 7 c) 125 g/mole ZnCO 3 3. a)? moles = (1 mole / 71.0 g) (86 g) = 1.2 moles Cl 2 (2 sig. figs.) b) 1.62 moles TeO 2 c) moles CF 4 4. a)? g = (17.0 g / mole) (8 moles) = 100 g NH 3 (1 sig. fig.) b) 320 g HNO 3 c) 1.8 g HCl 5. a)? molecules = (6.02 x atoms / mole) (4.5 moles) = 2.7 x atoms Ne b) 9.03 x molecules NO 2 c) 3.01 x molecules SF 2 6. a)?g = (190.2 g / mole)(1 mole / 6.02 x atoms)(6.02 x atoms) = 1.90 x 10 4 g b) 8.84 g SiBr 4 c) 2.99 x g H 2 O

8 Mole Calculations Worksheet #2 1. How many moles of Na are in 42 g of Na? 2. How many moles of O are in 8.25 g of O? 3. How much does 2.18 mol of Cu weigh? 4. What is the mass of 0.28 mol of iron? 5. How many atoms are in 7.2 mol of chlorine? 6. How many atoms are in 36 g of bromine? 7. How many moles are in 1.0 x 10 9 atoms? 8. What is the mass of 1.20 x atoms of sulfur? 9. How many moles of CO molecules are in 52 g of CO? 10. How many moles of C 2 H 6 are in 124 g? 11. How many moles of CCl 4 are there in 56 g? 12. What is the mass of 2.50 mol of H 2 SO 4? 13. What is the mass of 0.25 mol of Fe 2 O 3? 14. How many molecules are there in 52 g of CO? 15. How many formula units are in 22.4 g SnO 2? 16. How many molecules are in 116 g CCl 4? 17. What is the mass of 3.01 x formula units of Fe 2 O 3? 18. What is the mass of 1.2 x molecules of CO? 19. How many O atoms are in 1.25 mol of SO 2? 20. How many moles of O atoms do you have when you have 1.20 x N 2 O 5 molecules? 21. How many formula units are in 5.33 mol of CuCl 2? 22. How many copper atoms are in 5.33 mol of CuCl 2? 23. How many moles of Cl atoms are in 5.33 mol of CuCl 2? 24. How many moles of CuCl 2 contain 1.2 x atoms of Cl? 25. How many O atoms are in 3.15 mol of SnO 2? 26. How many H atoms are in 17.5 g (NH 4 ) 2 C 2 O 4? Answers mol Na mol O g Cu g Fe x Cl atoms x Br atoms x mol g S mol mol mol g g x molecules x formula units x molecules g Fe 2 O x 10 2 g CO x O atoms mol O x formula units x Cu atoms mol of Cl atoms mol CuCl x O atoms x H atoms