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Chemical Quantities

Chemical Quantities. Chapter 7. How Do You Measure Matter?. By Counting By Measuring Mass Volume In Chemistry, we use a measuring unit called a mole. What is a Mole?. Well….not exactly!. What is a mole and how big is it?. Mole is abbreviated mol

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Chemical Quantities

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  1. Chemical Quantities Chapter 7

  2. How Do You Measure Matter? • By Counting • By Measuring • Mass • Volume • In Chemistry, we use a measuring unit called a mole. www.brainybetty.com

  3. What is a Mole? www.brainybetty.com

  4. Well….not exactly! What is a mole and how big is it? • Moleis abbreviatedmol • 1 mole = 6.02 x 1023 representative particles(atoms, particles, molecules, or formula units--ions) akaAvogadro’s number www.brainybetty.com

  5. How many moles of Mg is 1.25 x 1023 atoms of Mg? atoms moles 1.25 x 1023 atoms Mg x 1 mol Mg 6.02 x 1023 atoms Mg = 2.08 x 10-1 mol Mg

  6. How many atoms are in 2.12 mol of propane (C3H8)? Moles molecules atoms 2.12 mol C3H8 x 6.02 x 1023 molecules x 11 atoms 1 mol C3H81 molecule C3H8 = 1.40 x 1025 atoms

  7. The Molar Mass of a Substance • MOLAR MASS: the mass (in grams) of one mole of the substance • What is the molar mass of SO3? 1-S = 1 x 32.1 g = 32.1 g 3-O = 3 x 16.0 g = 48.0 g = 80.1 g • SO3 = 80.1 g/mol www.brainybetty.com

  8. How many grams are in 9.45 mol of N2O3? molesgrams 9.45 mol N2O3 x 76.0 g N2O3 = 718.2 g N2O3 1 mol

  9. What about a mole of gas? • One moleof anygasoccupies22.4 litersat STP • STP = Standard Temperature & Pressure • 273 K • 101.3 kPa • Examples of gases: O2, CO2, N2, H2 www.brainybetty.com

  10. Determine the volume, in liters, of 0.60 mol SO2 gas at STP. moles liters 0.60 mol SO2 x 22.4 L SO2 = 13 L SO2 1 mol

  11. The Mole Road Map Volume Mass MOLE Periodic Table 22.4 liters Gas @STP g/mol 6.02 x 1023 particles (atoms, molecules, formula units, etc.) Avogadro’s Number Rep. Particles

  12. Percent Composition of a Compound • PERCENT COMPOSITION: the percent by mass of each element in a compound % mass of element E = grams of element E x 100% grams of compound

  13. An 8.20 g piece of Mg combines completely with 5.40 g of oxygen to form a compound. What is the percent composition of this compound? % Mg = 8.20 g x 100 % = 60.3% 13.6 g % O = 5.40 g x 100 % = 39.7% 13.6 g

  14. Calculate the percent composition of C3H8. % C = 36.0 g x 100 % = 81.8% 44.0 g % H = 8.0 g x 100 % = 18.2 % 44.0 g www.brainybetty.com

  15. Calculating Empirical Formulas • EMPIRICAL FORMULA:lowest whole number ratio of the atoms of the elements in a compound H2O2 HO N2H4 NH2 CO2 CO2 www.brainybetty.com

  16. What is the empirical formula of a compound that is 25.9% nitrogen and 74.1% oxygen? STEP 1: Convert to moles. 25.9 g N x 1 mol N = 1.85 mol N 14.0 g N 74.1 g O x 1 mol O = 4.63 mol O 16.0 g O

  17. STEP 2: Determine the lowest whole-number ratio 1.85 mol N = 1 mol N 1.85 4.63 mol O = 2.50 mol O 1.85 STEP 3: Convert any fractions to whole numbers. N2O5

  18. Calculating Molecular Formulas • MOLECULAR FORMULA:Multiple of the empirical formula • Calculate the molecular formula of the compound whose molar mass is 60.0 g and empirical formula is CH4N. www.brainybetty.com

  19. Empirical formula mass = 30.0 g/mol (efm) Molar mass = molecular formula efm 60.0 g = 2 C2H8N2 30.0 g www.brainybetty.com

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