Chapter 3 Notes 3-1 - 1 Section 3.1-3.3 AP Chemistry 6.022...

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Unformatted text preview: 1 Section 3.1-3.3 AP Chemistry 6.022 X 6.022 23 2 S C OMETRY TOI HI - the study of the the quantitative aspects of chemical reactions. reactions. 3 Why are the atomic masses on the periodic table a decimal? You can’t have parts of atoms? 4 AVERAGE atomic mass • AAM: Average of the atomic masses of all the chemical element's isotopes as found in a particular environment, weighted by isotopic abundance. • AAM = (Mass A)(% abundance of A) + (Mass B)(% abundance of B) + etc… Atomic mass is the average of all the naturally occurring isotopes of that element Isotope . Symbol % in nature Mass Mass Carbon-12 Carbon-12 Carbon-13 Carbon-14 12C 13C 14C X X X 98.89% 1.11% <0.01% = = = 11.866 0.1443 0.1443 0.0014 Average Atomic Masses Average Carbon = 12.011 AAM Examples: • An element consists of 1.40% of an isotope with mass 203.973 amu, 24.10% of an isotope with mass 205.9745 amu, 22.10% of an isotope with mass of 206.9759 and 52.40% of an isotope with mass 207.9766 amu. Calculate the aam and identify the element. 6 7 AAM Example #2: • There are two isotopes of nitrogen , one with an atomic mass of 14.0031 amu and one with a mass of 15.0001 amu. What is the percent abundance of each? 8 The Mole • A counting unit • Similar to a dozen, except instead of 12, it’s 602 billion trillion 602,000,000,000,000,000,000,000 • 6.022 X 1023 (in scientific notation) • This number is named in honor of Amedeo Avagadro (1776 – 1856), who studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present. Just How Big is a Mole? 9 • Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles. • If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles. • If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole. The Mole • 1 dozen cookies = 12 cookies • 23 10 10 1 mole of cookies = 6.022 X 10 cookies 23 • 1 dozen cars = 12 cars • 1 mole of cars = 6.022 X 10 cars • 1 dozen Al atoms = 12 Al atoms 23 • 1 mole of Al atoms = 6.022 X 10 atoms Note that the NUMBER is always the same, but the MASS is very different! 11 11 Learning Check Learning Suppose we invented a new collection unit called a rapp. One rapp contains 8 objects. 1. How many paper clips in 1 rapp? a) 1 b) 4 c) 8 2. How many oranges in 2.0 rapp? a) 4 b) 8 c) 16 3. How many rapps contain 40 gummy bears? a) 5 b) 10 c) 20 12 12 1 mole C 1 mole H2O 1 mole NaCl 23 = 6.022 x 10 C atoms 23 2 = 6.022 x 10 H O molecules 23 = 6.022 x 10 NaCl “formula units” (technically, ionics are compounds not molecules so they are called formula units) Avogadro’s Number as Avogadro’s Conversion Factor Conversion 23 13 13 6.022 x 10 particles 1 mole or 1 mole 23 6.022 x 10 particles 14 14 Learning Check 1. Number of atoms in 0.500 mole of Al 0.500 mole of Al 6.022 x 10 atoms Al 1 mole of Al 23 23 = 3.011 x10 2.Number of moles of S in 1.8 x 1024 Satoms of Al atoms 1.8 x 1024 S atoms 1 mole of S =3.0 mol S 6.022 x 1023 atoms S 15 15 Molar Mass • The Mass of 1 mole (in grams) • Equal to the numerical value of the average atomic mass (get from periodic table) 1 mole of C atoms 1 mole of Mg atoms 1 mole of Cu atoms = = = 12.0 g 24.3 g 63.5 g 16 16 Learning Check! Find the molar mass (usually we round to the tenths place) A. 1 mole of Br atoms = B. 1 mole of Sn atoms = 79.9 g/mole 118.7 g/mole 17 17 Molar Mass of Molecules and Compounds Compounds Mass in grams of 1 mole equal numerically to the sum of the atomic masses 1 mole Ca x 40.1 g/mol + 2 moles Cl x 35.5 g/mol = 111.1 g/mol CaCl2 Learning Check! A. Molar Mass of K2O = ? Grams/mole 18 18 B. Molar Mass of antacid Al(OH)3 = ? Grams/mole 19 19 Learning Check Prozac, C17H18F3NO, is a widely used antidepressant that inhibits the uptake of serotonin by the brain. Find its molar mass. 20 20 Calculations with Molar Mass Calculations Grams Moles molar mass 21 21 Converting Moles and Grams Converting Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al? 3.00 moles Al ? g Al 22 22 1. Molar mass of Al 1 mole Al = 27.0 g Al 2. Conversion factors for Al 27.0g Al or 1 mol Al 1 mol Al 27.0 g Al 3. Setup 3.00 moles Al 27.0 g Al 1 mole Al Answer = 81.0 g Al 23 23 Learning Check! The artificial sweetener aspartame (Nutra-Sweet) formula C14H18N2O5 is used to sweeten diet foods, coffee and soft drinks. How many moles of aspartame are present in 225 g of aspartame? 24 24 Atoms/Molecules and Grams • Since 6.02 X 1023 particles = 1 mole AND 1 mole = molar mass (grams) • You can convert atoms/molecules to moles and then moles to grams! (Two step process) • You can’t go directly from atoms to grams!!!! You MUST go thru MOLES. 25 25 Calculations molar mass Grams Avogadro’s number Moles particles molecules Everything must go through Moles!!! 26 26 Atoms/Molecules and Grams How many atoms of Cu are present in 35.4 g of Cu? 35.4 g Cu 1 mol Cu 63.5 g Cu 23 6.02 X 1023 atoms Cu 1 mol Cu = 3.4 X 10 atoms Cu 27 27 Learning Check! How many atoms of K are present in 78.4 g of K? 28 28 Learning Check! What is the mass (in grams) of 1.20 X 1024 molecules of glucose (C6H12O6)? 29 29 Learning Check! How many atoms of O are present in 78.1 g of oxygen? 78.1 g O2 1 mol O2 6.02 X 1023 molecules O2 2 atoms O 32.0 g O2 1 mol O2 1 molecule O2 Mole Island 30 30 Flight 6022 Molar Mass Express Molecules, atoms grams 31 31 Percent Composition What is the percent carbon in C5H8NO4 (the glutamic acid used to make MSG monosodium glutamate), a compound used to flavor foods and tenderize meats? a) 8.22 %C b) 24.3 %C c) 41.1 %C 32 Chemical Formulas of Compounds32 (HONORS only) • Formulas give the relative numbers of atoms or Formulas moles of each element in a formula unit - always a whole number ratio (the law of definite proportions). proportions). NO2 NO 2 atoms of O for every 1 atom of N 1 mole of NO2 : 2 moles of O atoms to every 1 mole mole of N atoms mole • If we know or can determine the relative number If of moles of each element in a compound, we can determine a formula for the compound. determine Types of Formulas (HONORS only) 33 33 • Empirical Formula The formula of a compound that The expresses the smallest whole number ratio of the atoms present. ratio Ionic formula are always empirical formula • Molecular Formula The formula that states the actual The actual number of each kind of atom found in one number molecule of the compound. molecule To obtain an Empirical Formula To (HONORS only) (HONORS 34 34 1. Determine the mass in grams of each Determine element present, if necessary. element 2. Calculate the number of moles of each Calculate moles element. element. 3. Divide each by the smallest number of Divide moles to obtain the simplest whole number ratio. number 1. If whole numbers are not obtained in step 3), multiply through by the smallest number that will give all whole numbers number A sample of a brown gas, a major air pollutant, sample is found to contain 2.34 g N and 5.34g O. Determine a formula for this substance. Determine require mole ratios so convert grams to moles require mole moles of N = 2.34g of N = 0.167 moles of N moles 0.167 14.01 g/mole 14.01 moles of O = 5.34 g = 0.334 moles of O moles 5.34 16.00 g/mole 16.00 N 0.167 O 0.334 = NO 2 Formula: N O Formula: 0.167 0.334 35 35 0.167 0.167 (HONORS only) Calculation of the Molecular Formula (HONORS only) 36 36 A compound has an empirical formula compound of NO2. The colourless liquid, used in of The rocket engines has a molar mass of 92.0 g/mole. What is the molecular formula of this substance? of Empirical Formula from % Composition (HONORS only) (HONORS 37 37 A substance has the following composition by mass: 60.80 % Na ; 28.60 % B ; 10.60 % H What is the empirical formula of the substance? Consider a sample size of 100 grams This will contain 28.60 grams of B and 10.60 grams H Determine the number of moles of each Determine the simplest whole number ratio ...
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This note was uploaded on 01/10/2011 for the course CHEM 103 taught by Professor Filipino during the Spring '10 term at University of Bridgeport.

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