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The MOLE

The MOLE. Describing Chemical Equations. Balanced chemical equations give us a ratio of particles 4 Fe + 3 O 2  2 Fe 2 O 3 A ratio of particles is not practical from our perspective. Describing Chemical Equations.

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The MOLE

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  1. The MOLE

  2. Describing Chemical Equations • Balanced chemical equations give us a ratio of particles • 4 Fe + 3 O2 2 Fe2O3 • A ratio of particles is not practical from our perspective

  3. Describing Chemical Equations • Atoms and molecules are very, very small, but we still need to “count” them. • Scientists instead weigh out an approximate number atoms

  4. The Mole • The mole is a quantity; it is used to “count” atoms and molecules. • A mole contains 6.02 x 1023 things • This is Avogadro’s number = 6.02214199 × 1023

  5. 1 mole of Al atoms = 6.02 x 1023 Al atoms • 1 mole H2O molecules = 6.02 x 1023 H2O molecules • 1 mole jelly donuts = 6.02 x 1023 jelly donuts • 1 mole of = 6.02 x 1023

  6. 6.02 x 1023 is a VERY large number

  7. 602,000,000,000,000,000,000,000

  8. Avogadro’s Number facts • Avogadro's number of inches is 1,616,434 light years, or across our galaxy and back 8 times. • Avogadro's number of seconds is about 19 quadrillion years, 4,240,666 times the age of the earth, or 954,150 times the age of the universe itself. • Avogadro's number of cents could repay the United States National Debt 86 million times. • Avogadro's number of kilograms is just over 20 times the mass of the earth

  9. Measuring Numbers of Atoms • We cannot count 6.02 x 1023 Al atoms. • We can, however, measure 26.98 grams of Al. • 26.98 grams of Al contains 6.02 x 1023 Al atoms • 26.98 grams of Al contains 1 mole of Al atoms

  10. Molar Mass • Molar mass of any element or compound = mass of 1 mole of that element or compound. • 26.98 grams is the molar mass of Al • The molar mass of any element is its atomic mass expressed in grams • Units are grams per mole (g/mol) • 26.98 is also the atomic mass of Al in amu.

  11. What’s the molar mass of? • Co • U • Pb • O2

  12. Molar Mass of a Compound • The molar mass of any compound is the sum of the atomic masses of the all the atoms in that compound • Expressed in grams per mole (g/mol). • The molar mass of H2O • 18.0 grams per mole.

  13. What’s the molar mass of? • Sodium Chloride • Magnesium Hydroxide • Iron (III) Oxide • Sulfuric Acid • Glucose

  14. Describing Chemical Equations • The ratio of particles remains the same if we substitute moles for molecules • 4 Fe + 3 O2 2 Fe2O3 • But what is the mass of the reactants and products in moles?

  15. Molar conversions: • Use dimensional analysis to convert • Moles to mass multiply by molar mass • Mass to moles divide by molar mass • Check to make sure units are correct • The magic formula: n = g / M

  16. Practice Molar Conversions • How many grams are in 15.5 moles of water ? • Find the mass of 0.650 moles of P2O5 • A large box of baking soda (sodium hydrogen carbonate) has a mass of 1.81 kg. How many moles are in the box?

  17. Solving Problems • How many grams are in 15.5 moles of water ? • Set up the formula: n = g / M where n = 15.5 g - ? and M = 18 • 18 is the formula weight of water. • So 15.5 = g / 18 • So g = 279 grams

  18. Particle and Mole Conversions: • Moles to Particles multiply by Avogadro’s number. • Particles to moles divide by Avogadro’s Number • Check units and use significant digits

  19. Practice Particle and Mole Conversions: • How many formula units are in 2.4 moles of methane? • A piece of marble (calcium carbonate) contains 8.47 x 1023 molecules. How many moles is this?

  20. Multi-step Conversions • Grams to Particles conversions are multi-step • Grams  Moles  Particles • How many particles are in an iron nail with a mass of • Particles to grams • Particles  Moles  Grams

  21. Practice Multi-step Converstions • There are approximately 8.27 x 1023 formula units of glucose in the human body. How much mass does this have? • How many particles are contained in in a 500.0 mL bottle of water?

  22. Molarity of Gases • To determine moles of gases it is difficult measure mass. • Instead chemists measure volume. • 1 Mole of gas has a volume of 22.4 Liters at standard temperature and pressure (STP).

  23. Practice • A 1.0 Liter bottle is filled with carbon dioxide at STP. How many moles is this? • A chemical reaction requires 1.7 moles of nitrogen gas. How many liters should be used at STP?

  24. Percent Composition • Percent that each part of a substance is of the whole, by mass • %part = (mass of part/mass of whole)x100

  25. Percent Composition Practice • Hydrochloric acid • Glucose • Decomposition results in 2.30 g Na, 1.60 g O, and 0.10 g H

  26. Empirical Formula • Empirical formula found by calculating the moles of each element in the compound. • If given a percent convert the percent to grams. • Divide each element in moles by the element with the least amount of moles

  27. Find the Empirical Formula • A compound is found to be 20% hydrogen and 80% carbon. • 7.30 g Na, 5.08 g S, 7.62 g O • 36.0 g C, 8.0 g O, 6.0 g H

  28. Molecular Formula • Formula expressing the true (actual) number of atoms in the compound. • True formula • A multiple of empirical formula • C6H6 = (CH)n where n = 6 • n = molar mass of molecule molar mass of empirical formula

  29. Find the Molecular Formula • The empirical formula for b-carotene is C5H7. The molar mass is 536 g/mol. Determine the molecular formula of b-carotene. • Ribose is 40.0% carbon, 6.67% hydrogen, and 53.3% oxygen. It has a molar mass of 150 g/mol. Determine the empirical and molecular formulas.

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