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Measuring Chemical Quantities: Moles, Mass, and Volume

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  1. Chapter 6 Chemical Quantities

  2. How you measure how much? • You can measure mass, • or volume, • or you can count pieces. • We measure mass in grams. • We measure volume in liters. • We count pieces in MOLES.

  3. Moles • Defined as the number of carbon atoms in exactly 12 grams of carbon-12. • 1 mole is 6.02 x 1023 particles. • Treat it like a very large dozen • 6.02 x 1023 is called Avagadro’s number.

  4. Representative particles • The smallest pieces of a substance. • For a molecular compound it is a molecule. • For an ionic compound it is a formula unit. • For an element it is an atom.

  5. Types of questions • How many oxygen atoms in the following? • CaCO3 • Al2(SO4)3 • How many ions in the following? • CaCl2 • NaOH • Al2(SO4)3

  6. Types of questions • How many molecules of CO2 are the in 4.56 moles of CO2 ? • How many moles of water is 5.87 x 1022 molecules? • How many atoms of carbon are there in 1.23 moles of C6H12O6 ? • How many moles is 7.78 x 1024 formula units of MgCl2?

  7. Measuring Moles • Remember relative atomic mass? • The amu was one twelfth the mass of a carbon 12 atom. • Since the mole is the number of atoms in 12 grams of carbon-12, • the decimal number on the periodic table is also the mass of 1 mole of those atoms in grams.

  8. Gram Atomic Mass • The mass of 1 mole of an element in grams. • 12.01 grams of carbon has the same number of pieces as 1.008 grams of hydrogen and 55.85 grams of iron. • We can right this as 12.01 g C = 1 mole • We can count things by weighing them.

  9. Examples • How much would 2.34 moles of carbon weigh? • How many moles of magnesium in 24.31 g of Mg? • How many atoms of lithium in 1.00 g of Li? • How much would 3.45 x 1022 atoms of U weigh?

  10. What about compounds? • in 1 mole of H2O molecules there are two moles of H atoms and 1 mole of O atoms • To find the mass of one mole of a compound • determine the moles of the elements they have • Find out how much they would weigh • add them up

  11. What about compounds? • What is the mass of one mole of CH4? • 1 mole of C = 12.01 g • 4 mole of H x 1.01 g = 4.04g • 1 mole CH4 = 12.01 + 4.04 = 16.05g • The Gram Molecular mass of CH4 is 16.05g • The mass of one mole of a molecular compound.

  12. Gram Formula Mass • The mass of one mole of an ionic compound. • Calculated the same way. • What is the GFM of Fe2O3? • 2 moles of Fe x 55.85 g = 111.70 g • 3 moles of O x 16.00 g = 48.00 g • The GFM = 111.70 g + 48.00 g = 159.70g

  13. Molar Mass • The generic term for the mass of one mole. • The same as gram molecular mass, gram formula mass, and gram atomic mass.

  14. Examples • Calculate the molar mass of the following and tell me what type it is. • Na2S • N2O4 • C • Ca(NO3)2 • C6H12O6 • (NH4)3PO4

  15. Using Molar Mass Finding moles of compounds Counting pieces by weighing

  16. Molar Mass • The number of grams of 1 mole of atoms, ions, or molecules. • We can make conversion factors from these. • To change grams of a compound to moles of a compound.

  17. For example • How many moles is 5.69 g of NaOH?

  18. For example • How many moles is 5.69 g of NaOH?

  19. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles

  20. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH

  21. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g

  22. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g • 1 mole NaOH = 40.00 g

  23. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g • 1 mole NaOH = 40.00 g

  24. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g • 1 mole NaOH = 40.00 g

  25. Examples • How many moles is 4.56 g of CO2 ? • How many grams is 9.87 moles of H2O? • How many molecules in 6.8 g of CH4? • 49 molecules of C6H12O6 weighs how much?

  26. Gases and the Mole

  27. Gases • Many of the chemicals we deal with are gases. • They are difficult to weigh. • Need to know how many moles of gas we have. • Two things effect the volume of a gas • Temperature and pressure • Compare at the same temp. and pressure.

  28. Standard Temperature and Pressure • 0ºC and 1 atm pressure • abbreviated STP • At STP 1 mole of gas occupies 22.4 L • Called the molar volume • Avagadro’s Hypothesis - at the same temperature and pressure equal volumes of gas have the same number of particles.

  29. Examples • What is the volume of 4.59 mole of CO2 gas at STP? • How many moles is 5.67 L of O2 at STP? • What is the volume of 8.8g of CH4 gas at STP?

  30. Density of a gas • D = m /V • for a gas the units will be g / L • We can determine the density of any gas at STP if we know its formula. • To find the density we need the mass and the volume. • If you assume you have 1 mole than the mass is the molar mass (PT) • At STP the volume is 22.4 L.

  31. Examples • Find the density of CO2at STP. • Find the density of CH4 at STP.

  32. The other way • Given the density, we can find the molar mass of the gas. • Again, pretend you have a mole at STP, so V = 22.4 L. • m = D x V • m is the mass of 1 mole, since you have 22.4 L of the stuff. • What is the molar mass of a gas with a density of 1.964 g/L? • 2.86 g/L?

  33. All the things we can change

  34. We have learned how to • change moles to grams • moles to atoms • moles to formula units • moles to molecules • moles to liters • molecules to atoms • formula units to atoms • formula units to ions

  35. Mass Moles

  36. Mass PT Moles

  37. Mass Volume PT Moles

  38. Mass Volume 22.4 L PT Moles

  39. Mass Volume 22.4 L PT Moles Representative Particles

  40. Mass Volume 22.4 L PT Moles 6.02 x 1023 Representative Particles

  41. Mass Volume 22.4 L PT Moles 6.02 x 1023 Representative Particles Atoms

  42. Mass Volume 22.4 L PT Moles 6.02 x 1023 Representative Particles Ions Atoms

  43. Percent Composition • Like all percents • Part x 100 % whole • Find the mass of each component, • divide by the total mass.

  44. Example • Calculate the percent composition of a compound that is 29.0 g of Ag with 4.30 g of S.

  45. Getting it from the formula • If we know the formula, assume you have 1 mole. • Then you know the pieces and the whole.

  46. Examples • Calculate the percent composittion of C2H4? • Aluminum carbonate.

  47. Empirical Formula From percentage to formula

  48. The Empirical Formula • The lowest whole number ratio of elements in a compound. • The molecular formula the actual ration of elements in a compound. • The two can be the same. • CH2 empirical formula • C2H4 molecular formula • C3H6 molecular formula • H2O both

  49. Calculating Empirical • Just find the lowest whole number ratio • C6H12O6 • CH4N • It is not just the ratio of atoms, it is also the ratio of moles of atoms. • In 1 mole of CO2there is 1 mole of carbon and 2 moles of oxygen. • In one molecule of CO2 there is 1 atom of C and 2 atoms of O.

  50. Calculating Empirical • Means we can get ratio from percent composition. • Assume you have a 100 g. • The percentages become grams. • Can turn grams to moles. • Find lowest whole number ratio by dividing by the smallest.

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