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THE MOLE

THE MOLE. How Scientists Keep Track of Atoms. One way to measure how much substance available is to count the # of particles in that sample However, atoms & molecules are extremely small Also, the # of individual particles in even a small sample is very large

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THE MOLE

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  1. THE MOLE

  2. How Scientists Keep Track of Atoms • One way to measure how much substance available is to count the # of particles in that sample • However, atoms & molecules are extremely small • Also, the # of individual particles in even a small sample is very large • Therefore, counting the # of particles is not a practical measure of amount • To solve this problem, scientists developed the concept of the mole • It’s the “chemical counting unit”

  3. Just as a dozen eggs equals 12 eggs, a mole = 602,000,000,000,000,000,000,000 • It is equal to that number no matter what kind of particles you’re talking about • It could be represent marbles, pencils, or bikes • usually deals with atoms and molecules • The word “mole” was introduced about 1896 by Wilhelm Oswald, who derived the term from the latin word moles meaning a “heap” or “pile.” • The mole, whose abbreviation is “mol”, is the SI base unit for measuringamount of a pure substance.

  4. The mole, as a unit, is only used to count very small items • Represents a # of items, so, we can know exactly how many items are in 1 mole • The experimentally determined number a mole is called, Avogadro’s Number. • Or6.02x1023 • The term representative particle refers to the species present in a substance • Usually atoms • Molecules • Or formula units(ions)

  5. CHEMICAL REP. PARTICLE REPRESENTATIVE SUBTANCE FORMULA PARTICLE IN 1 MOL

  6. How Do We Use The Mole? • We’d never use the mole to describe macroscopic or real world objects. • 1 mole (6.02x1023) of watermelon seeds would be found inside a watermelon the size of the moon. • 1 mole (6.02x1023) of donut holes would cover the earth and would be 5 miles deep. • Since the mole is such a huge number of items, it is only used to describe the amount of things that are very, very small. • 1 mole (6.02x1023) of water molecules would barely fill a shot glass

  7. x Using the mole in calculations #1 *Remember* 1 mol Mg = 6.02x1023 atoms Mg What number of moles of Mg is equivalent to 1.806x1024 atoms of Mg? 1.806x1024 atoms Mg 1 mole Mg 6.02x1023 atoms Mg (1.806x1024 atoms Mg)/(6.02x1023 atoms Mg) = 0.3x101 X = 3.0 moles

  8. x Using the mole in calculations #2 *Remember* 1 mol sugar = 6.02x1023 molecules sugar If we had 2.5 moles of sugar, how many molecules of sugar is that equal to? 2.5 moles sugar 6.02x1023 molec sugar 1 mole sugar (2.5 ) (6.02x1023 molec sugar) = X = 1.51x1024 molecules of sugar

  9. What if I asked you how many atoms are in a mole of a compound? • you must know how many atoms are in arepresentative particleor clusterof the compound. • To do this you must know the chem formula • For example, each molecule of CO2 is composed of1 C + 2 O’s = 3 atoms • 1 mole of carbon dioxide molecules contains avogadro’s number of carbon dioxide molecules. • Thus a mole of CO2 containsthree timesavogadro’s number of atoms

  10. To find the # of atoms in a mole of a compound, • You 1st determine the # of atoms in a representative particle of that compound • In a compound of water H2O • There are two water molecules for every one oxygen • That means if you have 1 mole of water • You have one mole of oxygen atoms • And two moles of hydrogen atoms • 1 mole of NH3(amonia) • Contains one mole of nitrogen and three moles of hydrogen

  11. Using the mole in calculations #3 • To find the # of atoms in a mol of a compound, • You 1st determine the # of atoms in a representative particle of that compound • And thenmultiplythat # of atoms by avogadro’s # How many atoms of carbon are in 2.12 mols of propane molecules (C3H8)? Useful Info: 1 mol C3H8 = 6.02x1023 molecules C3H8 1molecule C3H8 = 3 atoms of C

  12. x x Always start your dimensional analysis with what is given. In this case start with the 2.12 moles of C3H8 2.12 moles C3H8 6.02x1023molec C3H8 1 mole C3H8 3 atoms of C 1 molec C3H8 X = 3.83x1024 atoms of Carbon

  13. Do you know how to measure out 3 moles of sugar or salt or water? • The mole is a counting unit, so we would have to count out 6.02x1023 particles of each substance. (no thank you) • There are 2 ways we can use to measure out a number of moles of a substance. • Measure it in grams (a mass) • Or measure it in liters (a volume) How we measure moles…

  14. Using mass to measure moles… • One of the units we can use to measure out a particular amount of moles is to weigh it out in grams? • The only problem with this method is that 1 mol of books will weigh more than 1 mol of pencils, since each book is heavier. • What if 1 mol of pencils weighs 500Gtons and 1 mol of books weighs 1x106Gtons. • How much would 3.0 mols of pencils and 3 mols of books weigh? • 500 Gtons * 3 mols = 1500 Gtons pencils • 1x106 Gtons * 3 mols = 3x106 Gtons

  15. Using mass to measure moles… • To be able to measure out 1 mol of a substance we would need access to the known mass in grams of 1 mol of any substance in question • We would need a data table that provided all of these masses since every substance involved would have its own mass. • Remember, we don’t use the mole to count anything but atoms, molecules, etc. • So we need a table that provides the mass 1 mole would weigh for every combination of atoms known to man.

  16. Using mass to measure moles… • It just so happens that the periodic table provides us with some of that information. • The masses of each atom on the table is the equivalent to the mass of 1 mole of that atom • Every type of atom known to humankind is on that table. • The mass on the periodic table is called the molar mass (units of g/mol), because it represents the mass of 1 mol of that atom • 1 mole of Mg atoms weighs 24.305 g • 1 mole of C atoms weighs 12.011 g

  17. Using mass to measure moles… • That works well for atoms off of the periodic table, but how do we deal the molar masses of molecules and compounds? • Each of those compounds and molecules is composed of a combination of atoms • We have the molar masses for all of the atoms on the periodic table • We need to be able to add up the total weight of all of the atoms in the compound or molecule given its formula. • For ex, what is the molar mass of H2O?

  18. We just add the molar masses of each of the atoms that make up the molecule • From the PT, we find that the molar mass of 1 mole of Hydrogen atoms is 1.0079 g. • We have 2 Hydrogen atoms per molecule of H2O, so our Hydrogen atoms total 2 * 1.0079 g or 2.0158 g per mole • The mass of 1 mole of oxygen atoms is 15.999 g. • We have only 1 atom of oxygen per mole-cule of H2O so our total mass of oxygen is 1 * 15.999 g or just 15.999 g per mol • Therefore 1 mole of H2O molecs would weigh, 2.0158g+15.999g= 18.0148g

  19. Ex #2: Calculating molar masses using chemical formulas What is the mass of 1 mole of C6H12O6? • The overall mass of 1 mole of C6H12O6 will be the molar mass of 6 Carbons + the molar mass of 12 Hydrogens + the molar mass of 6 Oxygens. 6 Carbons = 6 * 12.011 g = 72.066 g 12 Hydrogens = 12 * 1.0079 g = 12.095 g 6 Oxygens = 6 * 15.999 g = 95. 994 g 180.16 g/mole

  20. Even though for compounds and molecules we have to calculate a molar mass using the periodic table, they are considered given or known values. • We can use these molar masses in calculations in which we are either give moles and asked for its mass equivalent or given mass and asked for its mole equivalent. • If we are given an element we just use the mass from the periodic table • If we are given a formula instead we just calculate the molar mass of the molecule using the masses from the periodic table.

  21. x Using the mole in calculations #4 How much would 9.45 moles of N2O3 weigh? So where do we start??? We always start with what is given in the problem (2 x 14.007) + (3 x 15.999) 9.45 moles N2O3 76.011 g N2O3 = 1 mole N2O3 X = 718 grams of N2O3

  22. x Using the mole in calculations #5 We have 92.2g of FeO, how many moles is the equivalent of the given mass? 1 mole FeO 92.2 g FeO 71.846 g FeO X = 1.28 moles of FeO

  23. Using volume to measure moles… • The other unit we can use to measure out mols is to measure a gas in Liters • There is a standard volume that 1 mol of any gas will occupy called molar volume. • If we had 1 mol of Ne and 1 mol of CO2 they would each contain 6.02x1023 particles, and occupy the same volume under standard conditions (0°C, 1 atm). • At STP or standard temp & press; 1 mol of any gas occupies 22.4 Liters of space • 1 mol of He = 22.4 L of space • 1 mol of N2 = 22.4 L of space

  24. x Using the mole in calculations #6 *Remember* 1 mol CO = 22.4 L CO What volume, in Liters, would .500 mols of CO gas occupy at STP? 22.4 L CO .500 mol CO 1 mole CO X = 12.2 L of CO

  25. Volume of Gas at STP Volume of Gas at STP Representative Particles Representative Particles 1 mole 1 mole Mole Mole 1 mole 1 mole 22.4 L 22.4 L 23 23 6.02x10 6.02x10 atomic atomic 22.4 L 22.4 L 1 mole 1 mole 1 mole 1 mole mass mass 23 23 atomic atomic 1 mole 1 mole 6.02x10 6.02x10 mass mass 1 mole 1 mole Mass Mass

  26. Using the mole in calculations #7 If you have a 35.67g piece of Chromium metal on your car, how many atoms of Chromium are in this piece of metal? • You are given mass and asked fornumber of particles • Let’s get some strategy

  27. Volume of Gas at STP Volume of Gas at STP Representative Particles Representative Particles 1 mole 1 mole Mole Mole 1 mole 1 mole 22.4 L 22.4 L 23 23 6.02x10 6.02x10 atomic atomic 22.4 L 22.4 L 1 mole 1 mole 1 mole 1 mole mass mass 23 23 atomic atomic 1 mole 1 mole 6.02x10 6.02x10 mass mass 1 mole 1 mole Mass Mass

  28. Volume of Gas at STP Volume of Gas at STP Representative Particles Representative Particles 1 mole 1 mole Mole Mole 1 mole 1 mole 22.4 L 22.4 L 23 23 6.02x10 6.02x10 atomic atomic 22.4 L 22.4 L 1 mole 1 mole 1 mole 1 mole mass mass 23 23 atomic atomic 1 mole 1 mole 6.02x10 6.02x10 mass mass 1 mole 1 mole We are given a mass Mass Mass

  29. Volume of Gas at STP Volume of Gas at STP Representative Particles Representative Particles 1 mole 1 mole Mole Mole We are asked for atoms 1 mole 1 mole 22.4 L 22.4 L 23 23 6.02x10 6.02x10 atomic atomic 22.4 L 22.4 L 1 mole 1 mole 1 mole 1 mole mass mass 23 23 atomic atomic 1 mole 1 mole 6.02x10 6.02x10 mass mass 1 mole 1 mole We are given a mass Mass Mass • It’s going to take us 2 conversions, we just need to follow the arrows

  30. x x • 1st we must use our mole map to convert from grams to moles then from moles to particles (atoms) • So we need to use the periodic table to calculate the mass of 1 mole of Chromium • One mole of chromium has a molar mass of 51.996g 35.67 g atoms Cr 1 mole Cr 51.996 g Cr 6.02x1023 atoms Cr X = 4.13x1023 atoms Cr = 1 mole Cr

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