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6.01 Atomic Vs. Macroscopic Scale Chemical Composition Atoms, Molecules, Moles and Grams Dr. Fred O. Garces Chemistry 152 Miramar College 1 Chemical Composition 05.2015 Atomic Mass Unit What is the mass of an object that cannot be seen ? What scale / units of mass is used for such small objects ? Unit of mass that is comparable to object of that size. atomic mass unit (amu) has been used as a standard for a mass of an atom. 1 amu = 1.66 • 10-27 Kg = 1/12 mass of 12C Atoms: Atomic mass one atom of potassium 39K weighs 39 amu. one atom of zinc 65Zn weighs 65 amu. Molecule: Molecular mass (or Formula Weight or Molecular Weight) one water (H2O) molecule 2-H, 1-O = 2amu + 16amu = 18 amu one glucose (C6H12O6) molecule: 6C, 12H, 6O = [6 C •12amu] + [12 H • 1 amu] + [6 O • 16amu] = 180 amu 2 Chemical Composition 05.2015 Isotopic Distribution Isotopic Distribution: Question comes to mind: Why is the mass of carbon 12.011 according the periodic table ? Why is the mass of chlorine 35.453 ? That of copper 63.546 ? Is not the mass of an atom reflected on the number of protons and neutrons an atom possesses? If so, is there such a thing as 0.011 amu of subatomic proton or neutron for carbon or 0.453 in chlorine and 0.546 in copper? Atomic mass, as shown in the periodic table, is the average of all isotope found in nature. Atomic mass is the weighted average mass for the isotropic distribution (found in nature) for that element. Weighted atomic mass average for the copper atom: Copper has two stable isotope: 63Cu - 72.70 %, and 65Cu - 27.30 % 63 amu • (0.7270) + 65 amu • (0.2730) = 63.546 amu 3 Chemical Composition 05.2015 Weighted Average The mass of the elements from the periodic table is actually the weighted average. Consider the following: 8 : 7 : 6 : 6 8 + 7 + - What is the average ? (Four points each rep 25%) 6 + 6 = 27 ! 27 / 4 = 6.75 or 8 (.25) + 7(.25) + 6(.25) + 6(.25) = 2 + 1.75 +1.5 + 1.5 = 6.75 (Also called a weighted average) Now what is the atomic mass for chlorine which exist in the following abundance: Cl-35 (75.53 % ) & Cl-37( 24.47 %) At. Wt = 35(.7553) + 37(.2447) = 26.44 + 4 9.05 Chemical Composition = 35.49 g/mol 05.2015 The Mole: A rice story The mole (a story of numbers) Moral of story: Rufus favorite food is rice. But he rarely eats it even though it is economical and easily prepared. He knows it is healthy for him and he was told once that it takes one serving is 12000 grains. So every time Rufus wants to eat rice he has to prepare 3 hr ahead of time and count out 12000 grains. How can we help my friend Rufus? 1 grain of rice weights an average of 19 mg. Count rice by weighing Mass = 12000 grains ∗ 19 mg ∗ 1g 1 grain 1000mg Mass rice for 1 serving = 8.0 oz ∗ 16 oz 454 g Weighs out 8.0 oz. hand –full rice = 1 cup € 5 Chemical Composition 05.2015 Counting by mass Method of Counting by mass In chemistry we deal with such small particles we need a way to count these particles. Like in Rufus case, the most efficient way of counting very small items is by counting by mass. As it turns out if we take 6.02•1023 atoms of carbon-12, 12C and weight this amount, it weights exactly 12 grams. Similarly, 6.023•1023 35Cl atoms weighs exactly 35 g. 6.023•1023 16O atoms weighs exactly 16 g. It follows that if we take 6.023•1023 O2 molecules made from oxygen-16, that weighs 32 g O2. This 6.02•1023 is call 1 mole. It is a chemist dozen. (NAv) 1 mole of substance is equal to its formula weight (molar mass) in grams 6 Chemical Composition 05.2015 Size of a mole Size of one mole; 1 mole of sand fill city of SD 5 miles deep. Take 1 moles of pennies, distribute these to all 5 billion humans, we'd all be trillionaire. If placing these pennies end to end, it would stretch... (how far?) 1 penny = 2.0 cm Length of 1 mole of penny = = 2.0 cm ∗ 6.02• 1023 ∗ s ∗ 1 hr ∗ day ∗ yr 3• 1010 cm 3600s 24 hr 365 day = 1, 268, 391.7 light - years = 1.3 million light - years € A mole is a quantity 7 http://www.rhysy.net/Science/GChart1.jpg Chemical Composition 05.2015 Atomic Vs Macroscopic Scale What path relates the atomic scale to our Macroscopic scale ? Atomic Magnifier Macroscopic (amu) Atoms Molecules formula unit 8 (grams) Nav Nav Nav moles moles moles Chemical Composition Atomic Wt Molar mass Formula wt grams grams grams 05.2015 Questions Relating Atomic to Macroscopic Scale How many Carbon atoms (or molecules) in a certain mass of sample? 12 g C " 1mole " 6.02•1023 atoms 6 g C " 0.5 mole " 3.01•1023 atoms 200 g C " ? mole " ? Atoms Calculation- 1mole 6.02 • 1023 200g C • • = 1.0 • 1025 C atoms 12g C 1mole C € 9 Chemical Composition 05.2015 Atomic Scale Vs. Macroscopic Scale Atomic Scale " Atoms Magnifier Molecules 10 Macroscopic Scale Grams pounds 12C 1-atoms 12amu 12C 1-mole 12 grams H2O 1-molecule 18.0 amu H2O 1-mole 18.0 grams NaCl 1-Formula Unit 58.5 amu NaCl 1-mole 58.5 grams Chemical Composition 05.2015 Defining the “MOLE” What is a mole ? … SI base unit for amount. … 6.02•1023 anything. … a magnifier between the atomic scale and macroscopic scale. … a conversion factor. … a chemist dozen. … the sum of the atomic mass of all elements in a substance when the mass is expressed in grams. (Molar Mass) … the ratio of elements in a substance as indicated by its chemical formula. C7H5N3O6 … the ratio of elements combining in a chemical reaction as indicated by the balance equation. 4 KOH (aq) + 11 3 O2 (g) ! 4 KO2 (s) Chemical Composition + 1 H2 O 05.2015 Questions RelatingNumber of Molecules to Mass How much will 5.0•1026 molecules of H2O weight (g) ? Data: MW: 18.0 gH 2O = 1mole H 2O Nav: 1mole H 2O = 6.02·1023 molecules H 2O 5.0·1026 molecule H 2O 5.0·1026 molecule H 2O ∗ 1mole H 2O ∗ 18.0 gH 2O 6.02·10 molecules H 2O 1 mole H 2O 23 = 14,950 g ="15"kg What volume is this (L)? Data: Density : 14, 950 g H 2O ∗ 12 1.0 g = 1 mL , 1000ml = 1ml 1ml ∗ 1L 1.0 g 1000ml Chemical Composition = 15L 05.2015 Questions Relating Number of Molecules to Mass How much will 5.0•1026 molecules of H2O weight ? Data: MW: 18.0 gH 2O = 1mole H 2O Nav: 1mole H 2O = 1mole H 2O 18.0 gH 2O 6.02·1023 molecules H 2O 5.0·1026 molecule H 2O 5.0·10 molecule H 2O∗ 26 ∗ 6.02·10 molecules H 2O 1 mole H 2O 23 ! = !14,950 g = 15 kg What volume is this? Data: Density : 14, 950 g H 2O ∗ 13 1.0 g = 1L 1ml ∗ 1000ml = 1ml 1L 1.0 g 1000ml Chemical Composition = 15L 05.2015 Mole Relationship to Mass and Elements (p261) Atoms in the compound Compounds* W B Y D X C * Including elemental compounds, i.e., O2, S8, Fe 14 Chemical Composition 05.2015 Question Relating Number of molecules to moles of Substance i. What is the number of molecules in 2.9 moles of TNT ? TNT = C7H5N3O6 Mol.Wt. = 227.0 g/mol g 227.0 g = 1 mol ii How much will this amount of TNT molecules weigh (g) ? iii How many N-atoms are in 1.0 g of TNT ? Note that in TNT has formula C7H5N3O6: 1 mole C7H5N3O6 ≅ 7 mol C ≅ 5 mol H ≅ 3 mol N ≅ 6 mol O Next Slide to demonstrate Stoic Map 15 Chemical Composition 05.2015 Mole Relationship to Mass and Elements (p261) W B i What is the number of molecules in 2.9 moles of TNT ? TNT = C7H5N3O6 Mol.Wt. = 227.0 g/mol D Y D C ii How much will this amount of TNT molecules weigh ? D B iii How many N-atoms are in 1.0 g of TNT ? X C Note that in TNT: 1 mole C7H5N3O6 ≅ 7mol C ≅ 5mol H ≅ 3mol N ≅ 6mol O B X D 16 Chemical Composition Y 05.2015 Question Relating Number of molecules to moles of Substance i. What is the number of molecules in 2.9 moles of TNT ? TNT = C7H5N3O6 D 2.9mol TNT • € 6.02 • 1023 molc' TNT 1 mole TNT D 227.0 gTNT 1 mole TNT 1mole TNT 227g TNT • D € B = 658.3 g TNT = 660 g TNT iii How many N-atoms are in 1.0 g of TNT ? Note that in TNT: 1 mole C7H5N3O6 ≅ 7 mol C ≅ 5 mol H ≅ 3 mol N ≅ 6 mol O 1.0gBTNT • 17 C = 1.75 • 1024 molc' = 1.8 • 1024 molc' ii How much will this amount of TNT molc’ weigh ? 2.9mol TNT • € Mol.Wt. = 227.0 g/mol g 227.0 g = 1 mol 3mol N 1mol TNT • 6.02 • 1023 atoms Y Chemical Composition 1mol N = X = 7.96 •1021 N atoms= 8.0 •1021 N atoms 05.2015 Question Relating Number of molecules to moles of Substance i. What is the number of molecules in 2.9 moles of TNT ? TNT = C7H5N3O6 Mol.Wt. = 227.0 g/mol 6.02 • 1023 molc' TNT 2.9mol TNT • 1 mole TNT = 1.75 • 1024 molc' = 1.8 • 1024 molc' ii How much will this amount of TNT weigh ? € 2.9mol TNT • 227.0 gTNT iii How many N-atoms are in 1.0 g of TNT ? Note that in TNT: 1 mole C7H5N3O6 ≅ 7 mol C ≅ 5 mol H ≅ 3 mol N ≅ 6 mol O € 1.0g TNT • € 18 1 mole TNT = 658.3 g TNT = 660 g TNT 1mole TNT 227g TNT • 3mol N 1mol TNT • 6.02 • 1023 atoms 1mol N = = 7.96 •1021 N atoms= 8.0 •1021 N atoms Chemical Composition 05.2015 Moles and Molar Mass: Example #7.61-Ebbing a) Calculate the moles of chloride ions in 1.11 g of magnesium chloride. b) How many chloride ions are present? 1mole MgCl2 ≅ 1mol Mg+2 ≅ 2mol ClMg - 24.3 g/mol = 24.3 g/mol 2 Cl - 35.45 g/mol•2 = 70.9 g/mol Molar Mass (MgCl2) 95.2 g = 1mol D a) ! #∗! B " $ " b) 19 Chemical Composition ! ! #∗ " Y " $ ! " #∗! $ " # = &Answer' $ " Y $ # $ & ' = Answer X $ # " $ State the path 05.2015 Moles and Molar Mass: Example #7.61-Ebbing a) Calculate the moles of chloride ions in 1.11 g of magnesium chloride. b) How many chloride ions are present? 1mole MgCl2 ≅ 1mol Mg+2 ≅ 2mol Cl- 1.1 gBMgCl2 ∗ = 70.9 g/mol Molar Mass (MgCl2) = 95.2 g/mol 95.2g MgCl2 0.0231 Ymol Cl ions • - € 2 Cl - 35.45 g/mol•2 1mole MgCl2 b) 20 = 24.3 g/mol D a) € Mg - 24.3 g/mol ∗ 2mol Cl1mol MgCl2 Y Cl - ions = 0.0231 mol 6.02 •1023 Cl- ions 1mol Cl- ions Chemical Composition = 22 1.39 •10X Cl- ions 05.2015 Summary Counting by Weighing at a Glance: Counting and Weighing Atoms and Molecules Formula Mass Mole The sum of the atomic masses of atoms in a formula. The formula mass of glucose is: (6.0amu •12C) + (1.0amu •12H) + (16.0amu • 6O) = 1.80•102 amu Mole = Avogadro’s number of particles = 6.02•1023 1 Mole glucose = 6.02•1023 molc’ Molar Mass The formula mass of a substance in grams; containing = 6.02•1023 atoms or molecules or formula unit Molar mass of glucose = 180 g / mole. C6H12O6 Glucose 21 Chemical Composition Atomic Mass Unit 1 g = 6.02•1023 atomic mass unit 1 amu = 1/1 the mass of one 12C atom 05.2015