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Slide 2 IIIIIIIV Chapter 10 Chemical Quantities Slide 3 What is the Mole? n A unit of measurement used in chemistry. n A counting number like a dozen eggs, a ream of paper, a bushel of apples, etc. n A mole describes an amount of matter. Slide 4 Definition: n A mole of any element is defined as the number of atoms of that element equal to the number of atoms in exactly 12.0 grams of carbon-12. Slide 5 Atomic Mass n Mass of a single atom 10 -23 grams n Atomic Mass Unit (amu) is used to describe the atomic mass of an atom. n A scale was devised to express the mass of all the different atoms. n Based on the mass of an atom relative to carbon-12. Slide 6 n Atomic Masses are listed in the periodic table. Slide 7 n 1 atom of 12 C has a mass of 12.01 amu n 1 mole of 12 C has a mass of 12.01 grams What it means: Slide 8 n 1 atom of 35 Cl has a mass of 35.45 amu n 1 mole of 35 Cl has a mass of 35.45 grams What it means: Slide 9 Formula Mass n Is calculated using the atomic mass of each element in the compound, times how many atoms of each element are in the compound. Slide 10 Example: n Find the formula mass of H 2 O H = 2 x 1.0 = 2.0 grams O = 1 x 16.0 = 16.0 grams 18.0 grams/mole Slide 11 Example: n Find the formula mass of NaOH Na = 1 x 23.0 = 23.0 grams O = 1 x 16.0 = 16.0 grams 40.0 grams/mole H = 1 x 1.0 = 1.0 grams Slide 12 The Atomic Mass or Formula Mass n Tells the mass in grams of 1 mole of a substance Slide 13 n There are 6.02 x 10 23 objects in one mole. n 602,000,000,000,000,000,000,000 Slide 14 n 1 mole of hockey pucks would equal the mass of the moon! A. What is the Mole? n 1 mole of pennies would cover the Earth 1/4 mile deep! n 1 mole of basketballs would fill a bag the size of the earth! Slide 15 A mole of sugar A mole of water A mole of copper Slide 16 Example: 16.0 g of oxygen 1 mole of oxygen 6.02 x 10 23 atoms of oxygen = = Slide 17 Example: 18.0 g of water 1 mole of water 6.02 x 10 23 molecules of water = = Slide 18 Example: 40.0 g of NaOH dissolved in water 1 mole of Na + ions and 1 mole of OH - ions 6.02 x 10 23 Na + ions and 6.02 x 10 23 OH - ions = = Slide 19 Molar Mass n Mass in grams of 1 mole of a substance. Slide 20 Molar Mass Examples n water n sodium chloride H2OH2O 2(1.01) + 16.00 = 18.02 g/mol NaCl 22.99 + 35.45 = 58.44 g/mol Slide 21 Molar Mass Examples n sodium bicarbonate n sucrose NaHCO 3 22.99 + 1.01 + 12.01 + 3(16.00) = 84.01 g/mol C 12 H 22 O 11 12(12.01) + 22(1.01) + 11(16.00) = 342.34 g/mol Slide 22 Molar Conversions molar mass (g/mol) MASS IN GRAMS MOLES NUMBER OF PARTICLES 6.02 10 23 (particles/mol) x x Slide 23 Molar Conversion Examples n How many moles of carbon are in 26 g of carbon? 26 g C 1 mol C 12.01 g C = 2.2 mol C Slide 24 Molar Conversion Examples n How many molecules are in 2.50 moles of C 12 H 22 O 11 ? 2.50 mol 6.02 10 23 molecules 1 mol = 1.51 10 24 molecules C 12 H 22 O 11 Slide 25 Molar Conversion Examples n Find the mass of 2.1 10 24 molecules of NaHCO 3. 2.1 10 24 molecules 1 mol 6.02 10 23 molecules = 293 g NaHCO 3 84.01 g 1 mol Slide 26 IIIIIIIV Suggested Reading: Pages 305 - 313 Chapter 10 % Composition, Empirical and Molecular Formulas Slide 27 Percentage Composition n the percentage by mass of each element in a compound Slide 28 100 = Percentage Composition %Cu = 128g Cu 160 g Cu 2 S 100 = %S = 32 g S 160 g Cu 2 S 80% Cu 20% S n Find the % composition of Cu 2 S. Slide 29 %Fe = 28 g 36 g 100 = 78% Fe %O = 8.0 g 36 g 100 = 22% O n Find the percentage composition of a sample that is 28 g Fe and 8.0 g O. Percentage Composition Slide 30 n How many grams of copper are in a 38.0-gram sample of Cu 2 S? (38.0 g Cu 2 S)(0.80) = 30.4 g Cu Cu 2 S is 80% Cu Percentage Composition Slide 31 100 = %H 2 O = 36 g 146 g 25% H 2 O n Find the mass percentage of water in calcium chloride dihydrate, CaCl 2 2H 2 O? Percentage Composition Slide 32 Empirical Formula C2H6C2H6 CH 3 reduce subscripts n Smallest whole number ratio of atoms in a compound Slide 33 Empirical Formula 1. Find mass (or %) of each element. 2. Find moles of each element. 3. Divide moles by the smallest # to find subscripts. 4. When necessary, multiply subscripts by 2, 3, or 4 to get whole #s. Slide 34 Empirical Formula Song (to help you remember steps) 1. Percent to Mass 2. Mass to Mole 3. Divide by Small 4. Multiply til Whole Slide 35 Empirical Formula n Find the empirical formula for a sample of 25.9% N and 74.1% O. 25.9 g 1 mol 14 g = 1.85 mol N 74.1 g 1 mol 16 g = 4.63 mol O 1.85 mol = 1 N = 2.5 O Slide 36 Empirical Formula N 1 O 2.5 Need to make the subscripts whole numbers multiply by 2 N2O5N2O5 Slide 37 Molecular Formula n True Formula - the actual number of atoms in a compound CH 3 C2H6C2H6 empirical formula molecular formula ? Slide 38 Molecular Formula 1. Find the empirical formula. 2. Find the empirical formula mass. 3. Divide the molecular mass by the empirical mass. 4. Multiply each subscript by the answer from step 3. Slide 39 Molecular Formula n The empirical formula for ethylene is CH 2. Find the molecular formula if the molecular mass is 28.1 g/mol? 28.1 g/mol 14 g/mol = 2.00 empirical mass = 14.03 g/mol (CH 2 ) 2 C 2 H 4