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The Mole: Avogadro’s number

The Mole: Avogadro’s number. How much is:. A dozen? 12 A century? 100 A mole? 6.02 x 10 23 (602,000,000,000,000,000,000,000). Can you count a mole of pennies?. If you could count 5 per second, it would take you

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The Mole: Avogadro’s number

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  1. The Mole: Avogadro’s number

  2. How much is: • A dozen? • 12 • A century? • 100 • A mole? • 6.02 x 1023 (602,000,000,000,000,000,000,000)

  3. Can you count a mole of pennies? • If you could count 5 per second, it would take you • 6.02 x 10 23 ÷ 5 pennies/second ÷ 60 sec/min ÷ 60 min/hr ÷ 24hrs/day ÷ 365 days/yr = • 3,800,000,000,000,000 years!

  4. Can you spend a mole of dollars? • If you could spend $1,000,000 every second it would take you • 6.02 x 10 23 ÷ $1,000,000/sec ÷ 60 sec/min ÷ 60 min/hr ÷ 24hrs/day ÷ 365 days/yr = • 19,000,000,000 years!

  5. When measuring amounts, you can count or you can mass them. If I want 2 dozen baseballs, I can count 24 baseballs Or I can mass 16 kg of baseballs.

  6. How many tennis balls are in 6 kg? 24 ( 2 dozen)

  7. How many tennis balls are in a mole? 6.02 x 10^23 in a mole 12 in a dozen

  8. Since we can’t count a mole of atoms, we MUST mass chemicals to measure moles 6.02 x 10 23 atoms of sulfur 32.07 grams of sulfur 6.02 x 10 23 atoms of carbon 12.01 grams of carbon

  9. How do we measure moles? • mole = number of particles equal to the number of atoms in 12 g of C-12 • 1 atom of C-12 weighs exactly 12 amu • 1 mole of C-12 weighs exactly 12 g • The number of particles in 1 mole is called Avogadro’s Number = 6.0221421 x 1023 • 1 mole of C atoms weighs 12.01 g and has 6.022 x 1023 atoms • the average mass of a C atom is 12.01 amu

  10. How do we measure moles? • The atomic mass on your periodic table is the mass of a mole of atoms of that element. • What is the mass of a mole of copper atoms? • 63.55 g • So, to count 6.02 x 1023 copper atoms, we mass out 63.55 g on the scale.

  11. 1 mole Sulfur 32.06 g 1 mole Carbon 12.01 g Mole and Mass Relationships

  12. Find the mass of: • A mole of silicon atoms • 28.09 g • 6.02 x 1023 atoms of nitrogen • 14.01 g • 6.02 x 1023 atoms of sodium • 22.99g • 2 moles of sodium atoms • 45.98 g

  13. How many atoms are in: • A mole of silicon • 6.02 x 1023 • 14.01 g of nitrogen • 6.02 x 1023 • 2 moles of sodium • 12.04 x 1023 • 45.98 g of sodium • 12.04 x 1023

  14. How many things are in: • A mole of footballs • 6.02 x 1023footballs • A mole of water • 6.02 x 1023 molecules • 2 moles of pencils • 12.04 x 1023 • ½ mole of lead • 3.01 x 1023 atoms

  15. Molar mass is the mass of one mole of a substance • To find the molar mass of an element, look on the periodic table. • To find the molar mass of a compound, add all the masses of its elements

  16. Chemical Formulas as Conversion Factors • 1 spider  8 legs • 1 chair  4 legs • 1 H2O molecule  2 H atoms  1 O atom

  17. Molar Mass of Compounds • the relative weights of molecules can be calculated from atomic weights Formula Mass = 1 molecule of H2O = 2(1.0 amu H) + 16.0 amu O = 18.0 amu • since 1 mole of H2O contains 2 moles of H and 1 mole of O Molar Mass = 1 mole H2O = 2(1.01 g H) + 16.00 g O = 18.02 g

  18. Find the molar mass of: • Ammonium phosphate • NH4+ PO43- • (NH4)3PO4 • =42.03 +12.12 +30.97 +64.00 • =149.12g • Carbon dioxide • CO2 • = 12.01 + 32.00 • = 44.01 g

  19. Find the molar mass of: • Hydrogen gas • H2 • = 2.02 g • Elemental hydrogen • H • = 1.01 g

  20. Find the molar mass of: • Iron • Fe • = 55.85 g • Iron (III) hydroxide • Fe3+ OH- • Fe(OH)3 • = 55.85 + 48.00 + 3.03 • =106.88 g

  21. Converting to and from moles. • To convert between moles and particles, simply multiply or divide by Avogadro’s number. • 2.0 mol x (6.02 x 1023 particles/mol) = 1.2 x 1024 particles • 3.1 x 1024 particles x (1 mol/ 6.02 x 1023 particles) = 5.0 mol

  22. Remember unitfactors?

  23. Converting to and from moles. • Converting between moles and mass requires the molar mass of the substance from the periodic table. • Element: Ag = 107.97g/mol • Ionic compound: CaCl2 = 110.98 g/mol • Covalent compound: NO2 = 46.01 g/mol • Always keep at least two decimal places on all values taken from the periodic table.

  24. Converting to and from moles. • To convert from moles to grams, multiply by molar mass: • 0.500 mol H2O x (18.02g/mol) = 9.01g H2O • To convert from grams to moles, divide by molar mass: • 54g H2O x (1mol/18.02g) = 3.0 mol H2O

  25. Converting to and from moles. • For gases, use the fact that at STP, 1 mol of any gas has a volume of 22.4 Liters. • What is STP? Standard Temperature and Pressure • Standard Temperature = 273K or 0.0°C • Standard Pressure = 1 atmosphere = 760 mm Hg (barometric) = 101.325 kPa.

  26. Converting to and from moles. • To go from moles to volume, multiply by 22.4L. • 3.00 mol x (22.4L/mol) = 67.2L of gas • To go from volume to moles, divide by 22.4L • 44.8L x (1mol/22.4L) = 2.00 moles of gas

  27. Converting to and from moles. • A convenient tool for making these conversions is called a “mole map.” • With the mole at the center, we can put all of the aforementioned calculations together into one simple picture.

  28. The Mole Map Gas Volume @ STP # Particles  x 22.4L 6.02 x 1023  x Mole  Molar Mass x Mass

  29. Percent Composition • Percentage of each element in a compound • By mass • Can be determined from • the formula of the compound • the experimental mass analysis of the compound • the total mass of each element • The percentages may not always total to 100% due to rounding

  30. What percentage of water is Oxygen? • Formula of the compound * H2O • Mass of the compound * 2 (1.01 g/mol) + 16.00 g/mol = 18.02 g/mol • Mass of each element * H is 1.01 g/mol, O is 16.00 g/mol

  31. Mass Percent as a Conversion Factor • the mass percent tells you the mass of a constituent element in 100.0 g of the compound • the fact that NaCl is 39.0% Na by mass means that 100.0g of NaCl contains 39.0g Na • this can be used as a conversion factor • 100.0 g NaCl  39.0 g Na

  32. 100g MMA % A mass A (g) moles A moles A moles B 100g MMB % B mass B (g) moles B Empirical Formulas • The simplest, whole-number ratio of atoms in a molecule is called the Empirical Formula • can be determined from percent composition or combining masses • The Molecular Formula is a multiple of the Empirical Formula

  33. Hydrogen Peroxide Molecular Formula = H2O2 Empirical Formula = HO Empirical Formulas

  34. Benzene Molecular Formula = C6H6 Empirical Formula = CH Glucose Molecular Formula = C6H12O6 Empirical Formula = CH2O

  35. Finding an Empirical Formula • convert the percentages to grams • skip if already grams • convert grams to moles • use molar mass of each element • divide all by smallest number of moles • round or multiply all mole ratios by number to make all whole numbers • if ratio ?.5, multiply all by 2; if ratio ?.33 or ?.67, multiply all by 3, etc. • skip if already whole numbers

  36. Determine the empirical formula of a compound containing 80.0 grams of carbon and 20.0 grams hydrogen.

  37. Grams to moles

  38. Divide by smallest

  39. Write Empirical Formula CH3

  40. All these molecules have the same Empirical Formula. How are the molecules different?

  41. All these molecules have the same Empirical Formula. How are the molecules different?

  42. Molar Massreal formula Molar Massempirical formula = factor used to multiply subscripts Molecular Formulas • The molecular formula is a multiple of the empirical formula • To determine the molecular formula you need to know the empirical formula and the molar mass of the compound

  43. What is the molecular formula for ethane if it has a molar mass of 30.06 g/mol? CH3= 15.04 g/mol Molecular formula = 2 x the empirical formula C2H6

  44. Determine the Molecular Formula of Cadinene if it has a molar mass of 204 g and an empirical formula of C5H8

  45. Mole Day is October 23!

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