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the MOLE…

the MOLE…. Counting Atoms. Everything we’ve done so far in chemistry has dealt with individual atoms or molecules However, it isn’t practical to work with 1 atom or 1 molecule or even 1,000,000 atoms or molecles They are just too small!

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the MOLE…

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  1. the MOLE…

  2. Counting Atoms • Everything we’ve done so far in chemistry has dealt with individual atoms or molecules • However, it isn’t practical to work with 1 atom or 1 molecule or even 1,000,000 atoms or molecles • They are just too small! • Therefore, chemists don’t work with 1 atom or even 1,000,000 atoms, they work with a huge collection of atoms

  3. Counting Atoms • It is impractical to get caught up into working with 1 atom or 1 atom’s mass. • It makes more sense to work with a collection of atoms rather than individually • Scientists were challenged to figure out a way to define a universal collection of particles • And which could still be described in terms of a relative mass

  4. Oxygen: Counting Atoms • We’ve already got the periodic table with masses for each element • So how many atoms are in that collection (assuming gram masses) • That number of atoms would immediately connect all other atoms and give us measurable amounts

  5. Counting Atoms Hydrogen: Carbon:

  6. Counting Atoms • The number of atoms that are in the gram mass on the PT is called Avogadro’s Number • And is defined as 1 mole • The mole becomes a counting unit much like the dozen. • 1 dozen eggs = 12 eggs • 1 mole of eggs = 602,000,000,000,000,000,000,000 eggs

  7. Counting Atoms • The word “mole” was introduced by Wilhelm Oswald, who derived the term from the word moles meaning a “heap” or “pile.” • We are just defining the pile as con-taining 6.02x1023 items • Any time we are counting how many we have and we want to describe it in terms of moles than… 1 mole is always = 6.02 x 1023 items

  8. Counting Atoms • The mole, whose abbreviation is “mol”, is the SI base unit for measuring amount of a pure substance. • It’s used exclusively for counting atoms, molecules, ions, or other things that are extremely small • It’s the chemist’s six-pack or dozen. Many objects in our everyday lives come in similar counting units. • 1 ream = 500 sheets of paper • 1 pair of socks = 2 socks • 1 cube = 24 cans

  9. Counting Atoms • We will learn in the near future that when a chemist reasons through a chemical reaction (recipe) they think in terms of X number of mols of this compound reacts with Y number of mols of this compound. • So we need to know how to calculate the number of molecules or atoms are involved in that X number of mols

  10. Counting Atoms How many moles is equivalent to 1.355x1024 atoms of Au? Using the mole in calculations #1 unit equality: 1 mol Au = 6.02 x 1023 atoms Au

  11. Counting Atoms The desired conversion is: atoms moles 1 mole Au 1.355x1024 atoms Au 6.02x1023atoms Au = 2.251 mol Au

  12. Counting Atoms How many molecules of carbon dioxide is 0.0357 mols? Using the mole in calculations #2 unit equality: 1 mol CO2 = 6.02x1023 molecules of CO2

  13. Counting Atoms The desired conversion is: moles atoms 6.02x1023molecules CO2 0.0357 mols CO2 1 mole CO2 = 2.15x1022 molecules CO2

  14. Your Turn: • Make the following mole conversions using dimensional analysis • 0.0753 mols of Na to atoms • 2.55x1025 molecules of CO2 to mols • 1.89x1019 molecules of H2O to mols • 1.25 mols of O2 to molecules

  15. Counting Atoms • Now suppose you want to determine how many atoms are in a mol of a compound or molecule • To do this you must know how many atoms are involved in the molecule. • To determine the number of atoms represented in a molecule requires knowing the chemical formula • Eg, each molecule of Carbon Dioxide (CO2) is composed of 3 atoms

  16. Counting Atoms How many atoms of Carbon are in 2.12 mols of Propane (C3H8)? Using the mole in calculations #3 unit equalities: 1 mol C3H8 = 6.02x1023 molecules C3H8 1 molecule C3H8 = 3 atoms C

  17. The desired conversions are: Counting Atoms moles molecules  atoms 6.02x1023 molecules C3H8 3 atoms C 2.12 mols C3H8 1 molecule C3H8 1 mole C3H8 =3.83x1024 atoms C

  18. Your Turn: • Make the following mole conversions using dimensional analysis • How many atoms of Oxygen are there in 0.118 mols of CO2 • How many atoms of Oxygen are there in 1.223 Ca(NO3)2.

  19. Counting Atoms • We can’t literally count the number of atoms in a sample, but we can count them by mass • So, there needs to be a connection between the mass of a sample and the number of moles in that sample • If we weigh out a particular mass of a substance, that can represent a particular number of mols • If we weighed out 12.011 g of Carbon • It will represent 1 mole of Carbon and/or 6.02x1023 Carbon atoms

  20. 23 18.99g F atoms=1 mol F atoms=6.02x10 F atoms Counting Atoms • This allows us to use the mass off of the periodic table to represent the mass of 1 mole (or 6.02x1023 atoms) of that element • 1 mol of C atoms weighs 12.01 g • 1 mol of H atoms weighs 1.008 g • 1 mol of W atoms weigh 183.8 g

  21. Counting Atoms • This new understanding of mass from the periodic table is known as the gram molar mass, or molar mass. • Molar Mass = mass of 1 mole of atoms in grams • We have a list of every possible molar mass for any given element on the periodic table • This mass can be used as a conversion factor…1 mole = 1.0079 g H, etc.

  22. Counting Atoms • So what if we have a compound instead of an element? • How do we figure out the mass of a mole of a compound? • This would be called a molecular mass, formula mass, or still can be called a molar mass • All we need is the formula for a representative particle of the compound and the periodic table.

  23. Counting Atoms • For instance how do we calculate the mass of 1 mole of Ca(OH)2? • You can calculate the mass of a mol-ecule of Ca(OH)2 by breaking it up into individual pieces • We can start with Calcium, then 2 O’s, then 2 H’s…until we run out of pieces 40.09 Ca: (1)(40.09 g/mol) = + 31.98 O: (2)(15.99 g/mol) = H: (2)(1.008 g/mol) = + 2.016 74.09 g/mol

  24. Counting Atoms What is the MM of glucose (C6H12O6)? (6C’S)(12.011g/mol) = 72.066g/mol (12H’S)(1.008 g/mol) = 12.096g/mol 95.94g/mol (6O’S)(15.99 g/mol) = 180.1g/mol 1 mole of C6H12O6 or 6.02x1023 molecules of the compound –weighs 180.1 grams

  25. Practice Time: • Calculate the molar mass of each of the formulas • C9H20 • (NH4)2CO3 • Zn(C2H3O2)2 • CCl4

  26. Counting Atoms How many grams are in 9.45 mol of Dinitrogen Trioxide (N2O3) Using the molar mass in calculations: The only connection to N2O3 and its mass is how much 1 mol of the compound weighs. But, using it as a comparison we can calculate the mass of 9.45 mol.

  27. Counting Atoms Step 1: Determine the mass of 1 mol of N2O3 28.02g (2N’s)(14.01g) = (3O’s)(15.99g) = 47.97g 75.99g If 1 mole of N2O3 weighs 75.99g than how much will 9.45 mols of N2O3 weigh?

  28. Counting Atoms Step 2: Convert the given moles to grams using the Molar mass equality. 75.99 g N2O3 9.45 mol N2O3 1 mol N2O3 =718 g N2O3

  29. Counting Atoms Find the number of moles of 92.2g of Iron (III) Oxide (Fe2O3) The only connection to the mass of Fe2O3 and how that corresponds to mols is how that 1 mol of the compound weighs a certain # of grams. Using that we can figure out how many moles weigh 92.2 g

  30. Counting Atoms Step 1: Determine the mass of 1 mol of Fe2O3 111.7g (2Fe’s)(55.85g) = (3O’s)(15.99g) = 47.97g 159.67g If 1 mole of Fe2O3 weighs 157.67g than how many mols will weigh 92.2 g of Fe2O3?

  31. Counting Atoms Step 2: Convert the given mass to mols using the Molar mass equality 1 mol Fe2O3 92.2 g Fe2O3 159.67 g Fe2O3 =.577mol Fe2O3

  32. Practice Time: • Determine the number of mols of CO2 in 454 grams. • What is the mass of 1.488 mols of propane gas, C3H8? • How many mols of methane molecules, CH4, are in 80.45 grams of methane? • How many grams does 3.40x10-5mols of Na2CO3 weigh?

  33. Counting Atoms • Another generality about the mole is that with matter in the gas phase we can develop another equality. • Under the same conditions, equal volumes of gases contain equal numbers of particles. • 1 mol of a gas will occupy the same volume as 1 mol of any other gas under the same conditions.

  34. Molar Volume of a Gas 22.4 L 22.4 L 1 mole of any gas under the specific conditions of 0°C and 1 atm (STP) will occupy a volume of 22.4 L. 6.02x1023 molecules of CO2 6.02x1023 molecules of O2

  35. Counting Atoms What volume, in Liters, does 0.60 mol of SO2 gas occupy at STP? The only connection to the volume of any gas and how that corresponds to mols is that 1 mol of a gas occupies 22.4 Liters of space. Using that we can figure out the volume of 0.60 mols of a gas at STP.

  36. Counting Atoms Step 1: Use the equality 1 mol = 22.4 L to do the conversion 22.4 L SO2 0.60 moles SO2 1 mole SO2 = 13 L SO2

  37. Practice Time: • What volume is occupied by 12.5 mols of nitrogen gas at STP? • How many moles of gas would be in 15,000 L of air?

  38. Counting Atoms Aspartame is an artificial sweetener that is 160 times sweeter than sugar when dissolved in water. It is marketed as Nutra-Sweet (C14H18N2O5). • What number of molecules are in 5.0 mg of aspartame? • What number of atoms of nitrogen are in 1.2 g of aspartame? • What is the mass in g of 1 molecule of aspartame?

  39. Counting Atoms

  40. Your Turn: • What is the mass of 7.21x1021 molecules of silver acetate (AgC2H3O2)? • How many grams of neon gas will fill a room with a volume of 4000L at STP? • How many molecules are there in 122 g of Cu(NO3)2? • Which has the greater mass? • a. 9.5x1024 atoms of C • b. 2.1 mol Br2 • c. 1.86x1022 molecules of CCl4 • d. 59.5g Hg

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