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Section 3.3 The Mole: A Measurement of Matter

Section 3.3 The Mole: A Measurement of Matter. OBJECTIVES: Describe how Avogadro’s number is related to a mole of any substance. Section 3.3 The Mole: A Measurement of Matter. OBJECTIVES: Calculate the mass of a mole of any substance. What is a Mole?. You can measure mass , or volume ,

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Section 3.3 The Mole: A Measurement of Matter

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  1. Section 3.3The Mole: A Measurement of Matter • OBJECTIVES: • Describe how Avogadro’s number is related to a mole of any substance.

  2. Section 3.3The Mole: A Measurement of Matter • OBJECTIVES: • Calculate the mass of a mole of any substance.

  3. What is a Mole? • You can measure mass, • or volume, • or you can count pieces. • We measure mass in grams. • We measure volume in liters. • We count pieces inMOLES.

  4. Moles (abbreviated: mol) • 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 Avogadro’s number.

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

  6. Types of questions • How many molecules of CO2 are there 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 (gam) • Equals the mass of 1 mole of an element in grams • 12 grams of C has the same number of pieces as 1 gram of H and 56 grams of iron. • We can write this as 12 g C = 1 mole C • We can count things by weighing them.

  9. Examples • How much would 2.34 moles of carbon weigh? • How many moles of magnesium is 24 g of Mg? • How many atoms of lithium is 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 g 4 mole of H x 1 g = 4 g 1 mole CH4 = 12 + 4 = 16 g • The Gram Molecular Mass (gmm) of CH4 is 16 g • this is the mass of one mole of a molecular compound.

  12. Gram Formula Mass (gfm) • The mass of one mole of an ionic compound. • Calculated the same way as gmm. • What is the GFM of Fe2O3? 2 moles of Fe x 56 g = 112 g 3 moles of O x 16 g = 48 g The GFM = 112 g + 48 g = 160 g

  13. Section 3.3Mole-Mass and Mole-Volume Relationships • OBJECTIVES: • Use the molar mass to convert between mass and moles of a substance.

  14. Section 3.3Mole-Mass and Mole-Volume Relationships • OBJECTIVES: • Use the mole to convert among measurements of mass, volume, and number of particles.

  15. Molar Mass • Molar mass is the generic term for the mass of one mole of any substance (in grams) • The same as: 1) gram molecular mass, 2) gram formula mass, and 3) gram atomic mass- just a much broader term.

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

  17. 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.

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

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

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

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

  22. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 23 g 1 mol O = 16 g • 1 mole of H = 1 g

  23. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 23 g 1 mol O = 16 g • 1 mole of H = 1 g • 1 mole NaOH = 40 g

  24. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 23 g 1 mol O = 16 g • 1 mole of H = 1 g • 1 mole NaOH = 40 g

  25. For example • How many moles is 5.69 g of NaOH? • need to change grams to moles • for NaOH • 1mole Na = 23 g 1 mol O = 16 g • 1 mole of H = 1 g • 1 mole NaOH = 40 g

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

  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 • We need to compare them at the same temperature 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 • 1 mole = 22.4 L of any gas at STP

  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 8.8 g 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, then the mass is the molar mass (from PT) • At STP the volume is 22.4 L.

  31. Examples • Find the density of CO2 at 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 1 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. Summary • These four items are all equal: a) 1 mole b) molar mass (in grams) c) 6.02 x 1023 representative particles d) 22.4 L at STP Thus, we can make conversion factors from them.

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