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The Mole

The Mole. Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second?. Measuring the Amount of “Stuff”. Suppose you needed to measure the amount of sand in a child’s sandbox… You could count each grain of sand (the number of particles)

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The Mole

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  1. The Mole Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second?

  2. Measuring the Amount of “Stuff” • Suppose you needed to measure the amount of sand in a child’s sandbox… • You could count each grain of sand (the number of particles) • You could weigh the sand (mass) • You could measure how many bucket-fulls of sand there are (volume) • You could use moles to convert the number of particles to mass or to volume and vice versa

  3. 1 Mole = 6.02 x 1023 particles • Defining particles… • Elements have particles called Atoms • Compounds have particles called Molecules • Moles are like measuring cups

  4. Mollionaire Q: how long would it take to spend a mole of $1 coins if they were being spent at a rate of 1 billion per second? A: $ 6.02 x 1023 / $1 000 000 000 = 6.02 x 1014 payments = 6.02 x 1014 seconds 6.02 x 1014 seconds / 60 = 1.003 x 1013 minutes 1.003 x 1013 minutes / 60 = 1.672 x 1011 hours 1.672 x 1011 hours / 24 = 6.968 x 109 days 6.968 x 109 days / 365.25 = 1.908 x 107 years A: It would take 19 million years

  5. Comparing sugar (C12H22O11) & H2O Same 1 gram each 1 mol each volume? No, they have dif. densities. No, molecules have dif. sizes. mass? Yes, that’s what grams are. No, molecules have dif. masses # of moles? No, they have dif. molar masses Yes. # of molecules? No, they have dif. molar masses Yes (6.02x1023 in each) # of atoms? No, sugar has more (45:3 ratio) No

  6. Example: How many moles of magnesium is 1.25 x 1023 atoms of magnesium? • 1 mole Mg = 6.02 x 1023 atoms Mg • Use as a conversion factor in a t-table = 2.08 x 10-1 mol Mg

  7. Round Table Practice • What is Avogadro’s Number? • How many moles of sodium is 6.482 x 1023 atoms of sodium? • If there are 1.03 x 105 mol cesium, then how many atoms are there? • If there are 8.925 x 10-3 mol of sulfur, then how many atoms are there? • How many atoms are in 2.12 mol of propane (C3H8)? • You have 1.14 mol SO3. a)What is the name of this compound. b) How many atoms are there? • a) How many moles are there in 4.65 x 1024 molecules of NO2 b)What is the name of this compound?

  8. Answers to Round Table Practice • 6.02 x 1023 particles of a substance • 1.08 x 1010 mol Na • 6.20 x 1028 atoms Cs • 5.37 x 1021 atoms S • 1.40 x 1025 atoms in this sample of propane • a) sulfur trioxide, b) 2.75 x 1024 atoms • a) 7.72 mol NO2 b) nitrogen dioxide

  9. Homework Assignment • Section 10.1 wksht, • 9-14 pg. 296 • 3-4 pg. 291 • 5-6 pg. 292 • Finish Naming Compounds Review

  10. Molar Mass – Use the Periodic Table • The mass of one mole is called “molar mass” • Example: 1 mol Li = 6.94 g Li • This is expressed as 6.94 g/mol • What are the following molar masses? S SO2 Cu3(BO3)2 32.06 g/mol 64.06 g/mol 308.27 g/mol Calculate molar masses (to 2 decimal places) CaCl2 (NH4)2CO3 O2 Pb3(PO4)2 C6H12O6 Cu x 3 = 63.55 x 3 = 190.65 B x 2 = 10.81 x 2 = 21.62 O x 6 = 16.00 x 6 = 96.00 308.27

  11. Molar mass • The mass of one mole is called “molar mass” • E.g. 1 mol Li = 6.94 g Li • This is expressed as 6.94 g/mol • What are the following molar masses? S SO2 Cu3(BO3)2 32.06 g/mol 64.06 g/mol 308.27 g/mol Calculate molar masses (to 2 decimal places) CaCl2 (NH4)2CO3 O2 Pb3(PO4)2 C6H12O6 110.98 g/mol (Cax1, Clx2) 96.11g/mol(Nx2, Hx8, Cx1, Ox3) 32.00 g/mol (Ox2) 811.54 g/mol (Pbx3, Px2, Ox8) 180.18 g/mol (Cx6, Hx12, Ox6)

  12. Molar Mass – Don’t be fooled by other names! • Gram Atomic Mass (GAM) – molar mass of an element (all atoms are identical) • Gram Molecular Mass (GMM) – molar mass of a compound (atoms that are covalently bonded) • Gram Formula Mass (GFM) molar mass of an ionic compound (ions bound in specific simple mole ratios)

  13. Formula g/mol g mol (n) HCl 0.25 H2SO4 53.15 NaCl 3.55 Cu 1.27 Converting between grams and moles • If we are given the # of grams of a compound we can determine the # of moles, & vise-versa • In order to convert from one to the other you must first calculate molar mass • Use a t-table to decide which conversion factor to use. 36.46 9.1 98.08 0.5419 58.44 207 63.55 0.0200

  14. Homework Assignment • 10.2 wksht (mole mass problems – we’ll finish the rest tomorrow) • 7,8,15 pg. 296 • 18-19 pg. 299 • 24, 26, 27 pg. 303

  15. Mole Mass Practice Problems • How many moles are represented by 16.0 g of ethanol, C2H5OH? • How many grams of glucose are in 6.63 x 1023 molecules of glucose, C6H12O6? • How many moles of methanol, CH3OH, are in 6.53 x 1023 molecules of methanol? • How many moles of sodium chloride are in 16.0 g of sodium chloride? • How many molecules, of potassium hydroxide are in 40.6 g? • How many grams of chromic chloride are in 7.14 moles of chromic chloride?

  16. Volume of a Mole of Gas • Volume varies with a change in temperature of pressure • The volume of a gas is usually measured at Standard Temperature and Pressure, STP • Standard Temperature: 0 C • Standard Pressure: 101.3 kPa or 1 atm • At STP, 1 mole of any gas fills 22.4 L (molar volume of a gas) • 22.4 L of a gas at STP has 6.02 x 1023 particles

  17. Molar Density • Density = Mass . = grams . Volume milliliters • Molar Density will always have the same t-table except for the first square

  18. Example Problems • Humans take in oxygen to burn glucose and gain energy. The water and carbon dioxide produced in this reaction, called cellular respiration, are exhaled. • If 28 g of water is produced in this reaction, what volume of water vapor could be exhaled? • How many atoms are exhaled if 44.8 L of CO2 is released? • How many grams of oxygen is consumed in the reaction if the volume of oxygen inhaled was 250.0 mL?

  19. Homework Assignment • Finish 10.2 wksht • 20-21 pg. 301 • 22-23 pg. 302 • 25, 28-31 pg. 303

  20. Percent Composition: The relative amounts of each element in a compound expressed as a percent • Also called “percent by mass” • % means “part over whole” • Example: 8.2 g of Magnesium reacts completely with 5.40 g of Oxygen to form a compound. What is the percent composition of each element in the compound?

  21. Solution • Mass of MgO = 8.2 g + 5.40 g = 13.60 g • (because the law of conservation of mass is ALWAYS true)

  22. If all you are given is the formula or name of a compound, then you must use Molar Mass from the Periodic Table • Example: Calculate the % composition of propane, C3H8. • Molar mass of C3H8 = 44.0 g/mol • Mass of carbon = 3 x 12 = 36 g/mol • Mass of hydrogen = 8 x 1 = 8 g/mol

  23. Percent Composition can also be used as a conversion to solve for mass. • Calculate the mass of carbon in 82.0 g of propane C3H8 • Molar mass of C3H8 = 44 g/mol • Mass of carbon = 3 x 12 = 36 g/mol • %C in propane = 81.8%... So if there were 100 g of propane, 81.8g would be C = 67.1 g of C

  24. H H H H H H Na Na Na Na Cl Cl Cl Cl O O O O O O Empirical and Molecular Formulas Consider NaCl (ionic) vs. H2O2 (covalent) • Chemical formulas are either “simplest” (a.k.a. “empirical”) or “molecular”. Ionic compounds are always expressed as simplest whole number ratios, or formula units. • Covalent compounds can either be molecular formulas (H2O2) or empirical formulas (HO)

  25. Steps to Calculate the Empirical Formula • What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen? • Assume that the % given is equal to the number of grams. N = 25.9 g O = 74.1 g • Convert the number of grams to moles using GAM.

  26. Divide by the lowest number of moles to obtain the simplest whole number ratio • If necessary, multiply by a whole number to obtain a whole-number ratio 1 mol N x 2 = 2 mol N 2.5 mol O x = 5 mol O 5. Write the chemical formula using these whole number ratios N2O5

  27. Q - Write empirical formulas for propene (C3H6), ethene (C2H2), glucose (C6H12O6), octane (C8H14) • Q - Identify these as empirical formula, molecular formula, or both H2O, C4H10, CH, NaCl

  28. Answers Q - Write simplest formulas for propene (C3H6), C2H2, glucose (C6H12O6), octane (C8H14) Q - Identify these as simplest formula, molecular formula, or both H2O, C4H10, CH, NaCl A - CH2 A - H2O is both simplest and molecular C4H10 is molecular (C2H5 would be simplest) CH is simplest (not molecular since CH can’t form a molecule - recall Lewis diagrams) NaCl is simplest (it’s ionic, thus it doesn’t form molecules; it has no molecular formula) CH CH2O C4H7

  29. Determine the Molecular Formula • You must know the empirical formula. • You must also know the molar mass of the compound. • Divide the molar mass of the compound by the empirical formula mass • Example: Calculate the molecular formula of a compound whose molar mass is 60.0 g and empirical formula is CH4N. • CH4N = 30 g/mol (using periodic table) • ? = 60 g/mol • Need twice as much… multiply subscripts in chemical formula by two • C2H8N2

  30. Homework Assignment • 10.3 wksht • 32-33 pg. 306 • 34-35 pg. 307 • 36-37 pg. 310 • 38-39 pg. 312 • Pre-Lab Digenite Lab

  31. Digenite Lab – Choose Your Role • Alchemist – measures out materials, combines them, and heats them up • Mathematician – guides team through the calculations and provides calculator-support • Troubadour – tells the story of the lab through careful and detailed observations • Scribe – records team data on the class data table and ensures accurate information is recorded by each team member

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