Transcript moles
The Mole and Stoichiometry Chemistry gets Real…. Tough that is The “mole” A term for a certain number of something. Brainstorm other counting words! Dozen = 12 Pair = 2 Gross = 144 A “mole” of something is 6.02 x 1023 of something. 602, 000, 000, 000, 000, 000, 000, 000 Molecular Weight M.W. = the weight (in grams) of a mole of substance On your periodic tables Round to the nearest tenth Hydrogen is 1.00797 1.0 g/mol Mole Weight is an INTENSIVE property— doesn’t depend on amount Try these MW’s Ca H2 g 40.1 mol g 2 (1.0) = 2.0 mol BaF2 1 mole of Ca weighs 40.1 grams 1 mole of H2 weighs 2.0 grams g [137.3 + 2(19.0)] = 175.3 mol g MW of 2BaF2 is still 175.3 mol g 1 penny = 2.68 coin 6 pennies = 2.68 X 6 = 16.08 g 6 pennies = 2.68 coin g Avogadro’s Number NA = 6.02 x anything 1023 of Avogadro (1776-1856) 1 mole K = 39.10 grams MW of potassium = 39.1 g mol 1 dozen K = 12 atoms 1 mole K = 6.02 x 1023 atoms MW of CO2 = 44.0 3 moles of CO2 = g mol g 3moles 44.0 132.00 grams mol 3 moles of CO2 = ____ g/mol MW of nitrogen gas = N2 (g) = 44.0 g 2 ( 14.0) = 28.0 mol g mol Which elements exist as diatomic molecules? H2 N2 O2 F2 Cl2 Br2 I2 How Big Is The Mole? One mole of marbles would cover the entire Earth to a depth of fifty miles One mole of hockey pucks would equal the mass of the moon. One mole of rice grains is more than the number of grains of all crops grown since the beginning of time. If one mole of pennies was divided up equally between all the people on Earth, you would have enough money to spend a million dollars every hour, 24 hours a day, for your entire life. When you died, you would have spent less than half of your riches. ÷MW Lab 11 Formula Mass (g) MW g mol X NA Moles Molecules X#atoms Atoms AgNO3 15.00 169.9 0.088 5.3 x 1022 2.7 x 1023 KOH CO Na2SO4 18.98 47.00 185.00 56.1 0.34 28.0 1.68 142.1 1.30 2.0 x 1023 6.0 x 1023 1.0 x 1024 2.0 x 1024 7.8x 1023 5.4 x 1024 H2 1.00 2.0 0.50 Na2S NaOH 13.76 214.75 78.1 0.18 40.0 5.37 1.1 x 1023 3.3 x 1023 3.2 x 1024 9.6 x 1024 Pb Pb3(PO4)2 6.50 18.75 207.2 0.031 811.6 0.023 1.8 x 1022 1.8 x 1022 1.4 x 1022 1.8 x 1023 NaCl 62.25 58.5 1.06 6.6 x 1023 1.3 x 1024 3.0 x 1023 6 x 1023 Percent Composition A. Determined from Formulas (“Accepted Value”) Is NaCl 50.0% Na by weight? No, Na is 23.0 g/mole and Cl is 35.5 g/mole To Prove, % Na = MW Na X 100 MW NaCl 23 X 100 39.3% (35.5 23) Percent Composition from Formula % oxygen in CaCO3? 3(16) (48) X 100 47.9520% 48.0%O [40.1 12.0 3(16)] (100.1) Grams of Mg in 4.00 grams of MgO? First: Calculate % Mg in MgO 24.3 60.2977% 60.3%Mg (24.3 16) Second: Calculate g Mg in 4.00 g MgO 0.603(4.00 g ) 2.41gMg B. Experimental Percent Composition FROM DATA (“Experimental Value”) 4.00g of Ag2O is decomposed to yield 3.65g Ag. The Experimental % = ? The Accepted % = ? Your Experimental Error? Experimental % Ag Equation: 2 Ag2O 4 Ag 4.00 g 3.65 g + O2 Experimental % Ag: 3.65 g 91.25% 91.3% 4.00 g True (Accepted) %Ag MW Ag X 100 MW Ag 2O 2(107.9) (215.8) X 100 93.097% 93.1% [2(107.9) 16] 231.8 Percent Error? (experiment al value - accepted value) 91.3 93.1 X 100 X 100 1.9333% 1.9% accepted value 93.1 Empirical Formula Definition: The simplest formula indicating the mole ratio of elements in a compound Examples: H2O2 HO C6H6CH N2O4? NO2 CO2 ? CO2 Empirical Formula STEPS 1. Change grams to moles 2. Divide by the least # moles for a RATIO 3. Apply ratio to the formula Solving Empirical Formula— determined from gram composition A compound contains 0.90 g Ca and 1.60 g Cl 1.60 0.90 0.045 moles Cl 0.022 moles Ca 35.5 40.1 0.045 moles Cl 2 0.022 moles Ca CaCl2 Try This… 0.556 g Carbon and 0.0933 g Hydrogen 0.0933 0.0556 0.0933molesH 0.046molesC 1 12.0 0.0933 moles H 2 0.046 moles C CH2 Why is the Empirical Formula a ratio of small WHOLE numbers? Can’t have half of an atom Atoms combine as whole units Shows the simplest way that atoms can pair What formula would this ratio give? K = 0.26 moles N = 0.25 moles O = 0.78 moles Yields an Empirical Formula of… KNO3 Try This: 70.5 % Fe and 29.5 % O 1.26 moles Fe, 1.84 ___ ___ moles O Assume 100g of substance: 70.5 gof Iron 1.26moles Fe g 55.9 iron 1.26 moles mol FeO1.5 X2 29.5 gof Oxygen 1.84moles O g 16.0 oxygen 1.26 moles mol Fe2O3 Try This: 40.0% C 6.7% H 53.3% O 3.3 moles C, ___ 6.7 moles H, ___ 3.3 moles O ___ Assume 100g of substance: 40.00 gofcarbon 3.3molesC g 12.0 carbon mol After dividing by the least moles yields: CH2O Why doesn’t the ratio of the % give the empirical formula? Must account for differing masses of elements. Why does the ratio of the moles give the empirical formula? The ratio of the # of atoms normalizes for mass differences. Molecular Formulas Definiton: Formula of an actual compound as it exists in molecules. Benzene exists as C6H6 not CH. Hydrogen Peroxide exists as H2O2 not HO. Empirical Formula MW Empirical MW Molecular Molecular Formula HO 17 g/mol 34 g/mol H2O2 CHOCl2 100 g/mol 200 g/mol CClN2 X2 226.5 75.5 g/mol X 2 g/mol C2H2O2Cl4 C3Cl3N6 Why is the M.W. needed to determine the molecular formula? Need M.W. of actual compound to find how many each type of atom is in a molecule. Stoichiometry – The Big Leagues A. Define: Problem Solving involving mass-mass relationships in chemical changes Ex. How many grams of rust are formed when 12.00 g of Fe reacts with oxygen. B. Must use balanced equations for the correct mole ratios C. Coefficients yield the mole ratio!!! 2 H2 + O2 2 H2O 2 : 1 : 2 D. Example 4 Fe + 3 O2 2 Fe2O3 4 : 3 : 2 If 4 moles of iron rust, 2 moles of Fe2O3 will form If 8 moles of iron rust, 4 moles of Fe2O3 will form 1) Determine the mole ratio (from the balanced equation) Solving Mass-Mass Problems 2) Convert grams to moles 3) Apply the mole ratio 4) Convert moles to grams 28.00 g of iron yields ? g of rust? 0.50 moles 2:1 0.25 moles 4 Fe + 3 O2 2 Fe2O3 28.00 g g 55.8 mol 160.0 28.00 g Fe g 0.25moles mol 40.00 g2Fe ? g Fe O32O3 36.00 g of water resulted from ? g of methane? 1.00 moles 1:2 2.00 moles Balance CH4 + 2 O2 1mole 16.0 g 16.00 g mol ? g CH 16.00g of4methane CO2 + 2 H2O 36.00 g 2moles g 18.0 mol 36.00 g H2O Variation: 12 moles of oxygen combusting will yield how many grams of CO2? 2:1 12 moles CH4 + 2 O2 6 moles CO2 + 2 H2O 44.0 g 6moles mol ? g COg2CO2 264.00