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The Mole

The Mole. General Chemistry Fall 2009. 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

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The Mole

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  1. The Mole General ChemistryFall 2009

  2. 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.

  3. 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?

  4. 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!

  5. How fast can you count? • Do you think we can count to 6.02x1023? • Let’s try and figure out how long it would take us to count to 6.02x1023 • Who’s the fastest counter? • How should we do this task?

  6. 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

  7. 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 • 6.02x1023 atoms H = 1.001 g • 6.02x1023 atoms Fe = 55.8 g

  8. 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 • How many atoms are in a molecule of ammonia (NH3)? • 4 atoms • 1 N atom and 3 H atoms • Each molecule has 4 atoms • So 1 mole of ammonia gas contains 1 mole of NH3 molecules, but four times as many atoms, or 4 moles of atoms (1 mol N atoms and 3 mol H atoms)

  9. Mole Conversions • Chemists measure amounts of substances by volume or mass. • Because the mole measures both a mass and a number of particles (and volume, but that’s later), it is the central unit in converting the amount of substance from one type of measurement to another.

  10. 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

  11. 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!

  12. 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

  13. Discuss in your team • Make sure everyone understands how to convert from moles to particles (atoms + molecules) and vice versa. • You MUST come up with a question in your group about moles to particles conversions.

  14. 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

  15. 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

  16. 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)

  17. 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.

  18. 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 

  19. Moles to Grams Conversions MASS • How many moles are in 14 g LiOH? • How many moles are in 15 g N2? moles x g = g mol Molar Mass g x mol = moles g 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

  20. 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

  21. Discuss in your Team • Make sure everyone understands how to convert from moles to grams and vice versa. • You MUST come up with a question in your group about moles to grams conversions.

  22. 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

  23. 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

  24. Moles and Gases • At the same temperature and pressure, equal volumes of gases contain the same number of gas particles. • 1 mole of any gas at 0oC and 1 atm (Standard Temperature and Pressure; STP) has a volume of 22.4 L. • This volume, 22.4 L/mol, is called molar volume.

  25. Moles and Gases MASS PARTICLES • A student fills a 1.0-L flask with CO2 at STP. How many molecules of gas are in the flask? • Plan: 1) Convert from volume to moles using molar volume. 2) Then convert from moles to molecules using Avogadro’s number. Molar Mass Avogadro’s Number MOLES Molar Volume(22.4 L/mol) VOLUMEof gases at STP

  26. Moles and Gases • Let’s see how you did… • A chemical reaction produces 0.82 mole of oxygen gas. What volume will that gas occupy at STP? 1.0-L CO2 1 1 mol CO2 22.4 L CO2 6.02 x 1023 molec CO2 1 mol CO2 2.7 x 1022 molec. CO2 0.82 mol O2 1 22.4 L O2 1 mol O2 18 L O2

  27. Percent Composition • In your team discuss… • How many hours of sleep do you get a night? • What percentage of the day do you spend asleep? • As a team, write out how you figured out the percentage of each day you spend sleeping.

  28. Percent Composition • You can determine what part of the total mass of a compound is made up by each element in that compound. • Percent Composition- the mass of each element in a compound compared to the entire mass of the compound and multiplied by 100 percent.

  29. Determining % Composition • First method: Calculate from a given formula • Example: Water • 1 mole of water (H2O) • Molar mass= 18 grams • 2 moles of hydrogen atoms • 1 mole of oxygen atoms • To determine percent composition you need to determine what part of the total mass, 18 g, is made up of hydrogen atoms and what part is made up of oxygen atoms.

  30. Determining % Composition % of element = total mass of element in compound 100 total mass of compound • % of hydrogen= 2.0 g H x 100 = 11% 18.0 g H2O • % of oxygen = 16 g O x 100 = 89% 18.0 g H2O

  31. Determining % Composition • Second method: Experimental analysis (mass the whole sample, separate into parts through decomposition, mass the parts, follow same method as before) • A sample of an unknown compound with a mass of 0.2370 g was extracted from the roots of a plant. Decomposition produced 0.09480 g of carbon, 0.1264 g of oxygen, and 0.0158 g of hydrogen. What is the percent composition of the compound? • Plan: Determine the % of each element in the compound by dividing the mass of each element by the total mass of the sample, then multiply by 100. • % C = (0.0948 g / 0.2370 g) x 100% = 40.00% C • % O = (0.1264 g / 0.2370 g) x 100% = 53.33% O • % H = (0.0158 g / 0.2370 g) x 100% = 6.67% H

  32. Your Turn • Find the percent composition of a compound that contains 2.30 g of sodium, 1.60 g of oxygen, and 0.100 g of hydrogen in a 4.00-g sample of the compound. • % Na = (2.30 g / 4.00 g) x 100% = 57.5% Na • % O = (1.60g / 4.00 g) x 100% = 40.0% O • % H = (0.100 g / 4.00 g) x 100% = 2.50% H

  33. B D Moles of substance Number of particles Mass of substance • Use N as a unit factor: multiply by 1 mol/6.02x1023 • Use N as a unit factor: multiply by 6.02x1023/1 mol • Use molar mass as a unit factor: multiply by 1 mol/#g • Use molar mass as a unit factor: multiply by #g/1 mol • Use molar volume as a unit factor: multiply by 1 mol/22.4L • Use molar volume as a unit factor: multiply by 22.4L/1 mol A C E F Volume of gas (STP)

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