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The Mole

The Mole. The mole is the "counting unit" used by chemists to indicate the number of atoms, ions, molecules, or formula units present in a particular sample. The mole is similar to other counting units that you've used before....pair (2), dozen (12), and gross (144).

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The Mole

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  1. The Mole

  2. The mole is the "counting unit" used by chemists to indicate the number of atoms, ions, molecules, or formula units present in a particular sample. • The mole is similar to other counting units that you've used before....pair (2), dozen (12), and gross (144). • One mole of a compound contains Avogadro's number (6.022 x 1023) of molecules (molecular compound) or formula units (ionic compound).

  3. Owing to their tiny size, atoms and molecules cannot be counted by direct observation.

  4. A mole is always the same number but a mole of different substances will have different masses.

  5. A Mole of ParticlesContains 6.02 x 1023 particles 1 mole C 1 mole H2O 1 mole NaCl = 6.02 x 1023 C atoms = 6.02 x 1023H2O molecules = 6.02 x 1023NaCl formula units 2 x 6.02 x 1023 ions

  6. Measuring Moles • One-mole quantities of three substances are shown, each with a different representative particle. • The representative particle in a mole of water is the water molecule.

  7. The representative particle in a mole of sodium chloride is the formula unit.

  8. The representative particle in a mole of copper is the copper atom.

  9. 1.1.2 • Video • http://www.youtube.com/watch?v=qLHUTTtIE7A&list=PL5D32AAD026FB786F

  10. Atomic Mass • The mass of an atom is very very small: • oxygen atom 2.66 x 10-23 grams • hydrogen atom 1.67 x 10-24 grams

  11. Relative Atomic Mass • Although it is possible to measure the actual mass of an atom, it is more convenient to use relative masses. • The relative mass of an atom is a comparison of the atom’s mass to the mass of a carbon-12 atom. • Carbon-12 was chosen as the standard for measuring relative atomic masses.

  12. Atomic Mass Unit • The mass of a carbon-12 atom = exactly 12 u • One atomic mass unit (amu or u) =1/12 the mass of a carbon-12 atom.

  13. Molecular Mass • The sum of the atomic masses of all the atoms in a chemical formula. • Molecular mass of CO2 is: 12.01 + 2 x 16.00 = 44.01 u

  14. moles to particles Suppose you want to determine how many molecules of glucose (C6 H12O6 ) are in 3.50 moles of glucose. You know that one mole contains 6.02 x 1023 representative particles: 1 mole _______ 6.02 x 1023 molecules 3.5 _______ x

  15. Suppose you want to determine how many atoms of hydrogen are in of 3.50 moles of glucose (C6 H12O6 ). 1 mole _______ 6.02 x 1023x 12 hydrogen atoms 3.5 _______ x

  16. Calculate the number of moles that contain 4.50 x 1024 atoms of zinc (Zn):

  17. mass to moles • A roll of copper wire has a mass of 848 g How many moles of copper are in the roll? 1 mol Cu _____ 63.5g x _____ 848 g

  18. Calculate the mass of 0.625 moles of calcium nitrate.

  19. Calculate the number of molecules in 15.7 mol carbon dioxide.

  20. Molar Volume, V Avogadro’s Law states that: 1 mole of every gas occupies the same volume, at the same temperature and pressure. There are two standards, commonly used in schools: STP (standard temperature and pressure) which is 0 ºC and 1 atmosphere. RTP (room temperature and pressure) which is 20 ºC and 1 atmosphere. • The molar volume of a gas is 22.4 liters at STP (standard temperature and pressure). • The molar volume of gas is 24 dm3 at RTP (room temperature and pressure).

  21. Example: Calculate the volume of carbon dioxide gas, CO2, occupied by (a) 5 moles and (b) 0.5 moles of the gas occupied at STP.

  22. Calculate the number of moles of ammonia gas, NH3, in a volume of 80 L of the gas measured at STP.

  23. Gas Volume from Equations • http://www.onlinemathlearning.com/molar-volume.html

  24. Mole Ratio: • http://www.files.chem.vt.edu/RVGS/ACT/notes/The_Mole.html

  25. n= m/MM the unit for MM isgmol-1

  26. Learning Check

  27. Learning Check! • Molar Mass of K2O = ? Grams/mole B. MolarMass of antacid Al(OH)3 = ? Grams/mole

  28. Converting Moles and Grams Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?

  29. Learning Check! The artificial sweetener aspartame (Nutra-Sweet) formula C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame?

  30. Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? = 3.4 X 1023 atoms Cu

  31. Learning Check! How many atoms of K are present in 78.4 g of K?

  32. Learning Check! What is the mass (in grams) of 1 molecule of glucose (C6H12O6)?

  33. Learning Check! How many atoms of O are present in 78.1 g of oxygen?

  34. Volume of GasesAvogadro’s Law • http://www.chemistry.co.nz/avogadro.htm

  35. 2 liters of CO gas react with 1 liter of O2 gas to yield 2 liters of CO2 gas. 2 CO(g) + 1 O2(g)2 CO2(g) HOW CAN THIS BE POSSIBLE? Avogadro's Law : EQUAL VOLUMES OF DIFFERENT GASES CONTAIN EQUAL NUMBERS OF MOLECULES WHEN MEASURED AT THE SAME TERMPERATURE AND PRESSURE.

  36. One mole of any gas occupies 22.41L at 0oC and 1 atm(stp) and contains the same number of particles - atoms - molecules. 22.41L is know as molar volume. Molar Volume = 22.4 dm3 mol at s.t.p. And 24.0 dm3 mol at r.t.p.

  37. 1. What volume of carbon dioxide, measured at s.t.p. will be liberated from 5 g of calcium carbonate, by the action of an excess of dilute hydrochloric acid? 2. 120 cm3 of hydrogen gas is released at S.T.P. when a small amount of Magnesium is placed in excess dilute hydrochloric acid. What mass of Magnesium was added.

  38. Problems • 1. Calculate the molar volume of each of the following: a. 46.00 grams of nitrogen gas b. 200.0 grams of carbon monoxide c. 3.01 x 1023 molecules of ethane (C2H6)

  39. If the amount of gas in a container is increased, the volume increases. • If the amount of gas in a container is decreased, the volume decreases. • V1/n1 = V2/n2

  40. 5.00 L of a gas is known to contain 0.965 mol. If the amount of gas is increased to 1.80 mol, what new volume will result (at an unchanged temperature and pressure)? Answer: V1n2 = V2n1 (5.00 L) (1.80 mol) = (x) (0.965 mol)

  41. Percent Composition What is the percent carbon in C5H8NO4 (the glutamic acid used to make MSG (monosodium glutamate), a compound used to flavor foods and tenderize meats? a) 8.22 %C b) 24.3 %C c) 41.1 %C

  42. Chemical Formulas of Compounds • Formulas give the relative numbers of atoms or moles of each element in a formula unit - always a whole number ratio (the law of definite proportions). NO2 2 atoms of O for every 1 atom of N 1 mole of NO2 : 2 moles of O atoms to every 1 mole of N atoms • If we know or can determine the relative number of moles of each element in a compound, we can determine a formula for the compound.

  43. Types of Formulas(HONORS only) • Empirical Formula The formula of a compound that expresses the smallest whole number ratio of the atoms present. Ionic formula are always empirical formula • Molecular Formula The formula that states the actual number of each kind of atom found in one molecule of the compound.

  44. To obtain an Empirical Formula (HONORS only) 1. Determine the mass in grams of each element present, if necessary. 2. Calculate the number of moles of each element. 3. Divide each by the smallest number of moles to obtain the simplest whole number ratio. • If whole numbers are not obtained* in step 3), multiply through by the smallest number that will give all whole numbers *Be careful! Do not round off numbers prematurely

  45. A sample of a brown gas, a major air pollutant, is found to contain 2.34 g N and 5.34g O. Determine a formula for this substance. require mole ratios so convert grams to moles moles of N = 2.34g of N = 0.167 moles of N 14.01 g/mole moles of O = 5.34 g = 0.334 moles of O 16.00 g/mole Formula: (HONORS only)

  46. Calculation of the Molecular Formula(HONORS only) A compound has an empirical formula of NO2. The colourless liquid, used in rocket engines has a molar mass of 92.0 g/mole. What is the molecular formula of this substance?

  47. Empirical Formula from % Composition(HONORS only) A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; 10.60 % H What is the empirical formula of the substance?

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