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“THE MOLE” Counting Quantities 1.) You can count how many of something you have…… 12 doughnuts in a dozen 10 pins knocked down for a strike 2.) You can measure the mass of what you have……. buying candy by the pound gold is priced by the gram 3.) You can measure matter by volume….. gasoline by the liter medicine in mL “THE MOLE” (Molar Mass = 1 MOLE) A convenient standard quantity of a substance For solids, liquids, gases…..you can convert weight to moles, or moles to weight The amount of a substance = in grams to the sum of the atomic weights 1 mole =6.02 x 1023 particles • What do I mean when I say particles? –Can be atoms, molecules, formula units, or ions. ELEMENT use atoms COVALENT COMPOUND use molecules IONIC COMPOUND use formula units ION use ions Examples • Na – I mole of Na = 6.02 x 1023 atoms of Na • H 2O – 1 mole of H2O = 6.02 x 1023 molecules of H2O • NaCl – 1 mole of NaCl = 6.02 x 1023 formula units of NaCl • Cl– 1 mole of Cl- = 6.02 x 1023 ions of Cl- MOLAR MASS AND NUMBER OF PARTICLES Substance Carbon (C) Sodium (Na) Molar Mass Number of Particles in One Mole 12.0 g 6.02 x 1023 C atoms 23.0 g 6.02 x 1023 Na atoms CaCO3 (antacid) formula 100.1 g 6.02 x 1023 CaCO3 units C6H12O6 (glucose) 180.0 g 6.02 x 1023 glucose molecules C8H10N4O2 (caffeine) 194.0 g 6.02 x 1023 caffeine molecules Example problems • How many moles is 3.46 x molecules of water? 26 10 • How many moles of hydrogen are in 3.46 x 1026 molecules of water? • How many atoms is 3.46 moles of silver? A dozen… • Will a dozen trucks have the same mass as a dozen chocolates? • Will 6.02 x molecules of water have the same 23 mass as 6.02 x 10 molecules of CO2? 23 10 Atomic Mass Unit (AMU) • AMU = mass of a single atom • AMU are relative values based on the mass of the most common isotope of carbon. Molar Mass • More convenient to use UNITS: g/mol • MM= mass of one mole of a substance ….remember??? Molar Mass Use periodic table to find MM of a compound: 1. Multiply each element’s mass (from the periodic table) by number of atoms present 2. Add all the masses together Practice Problem • Find the molar mass of (NH4)2O Did you get 52 g/mol? • How many grams is 2.35 moles of MgO? Practice Problem • How does the amount of moles of 44 g of CO2 compare to 36.6 g of HCl? –Same amount of moles; therefore, same amount of 23 molecules (6.02 x 10 ) Example • How many moles is 300 g CO2? • 1. Determine the relationship between g CO2 and moles of CO2 (find molar mass) • 2. Cancel out units and solve. Solution 44 g CO2 = 1 mole CO2 300 g CO2 1 mole CO2 44 g CO2 = 6.82 mole CO2 Example • How many molecules is 6.82 moles CO2? • Determine the relationship between moles of CO2 and molecules CO2 (Avogadro’s number) • 2. Cancel out units and solve. Solution 23 molecules 6.02 x 10 6.82 mole CO2 1 mole CO2 = 4.11 x 1024 molecules CO2 • NOTICE: to get from grams to molecules you have to go through the MOLE – Remember in chemistry all roads lead to the mole! MOLAR VOLUME • PV=nRT – What is the volume of 1 mole of gas of oxygen at STP? – What is the volume of 1 mole of gas of hydrogen at STP? MOLAR VOLUME • Gases can change volume based on temperature and pressure • BUT at STP 6.02 x 1023 molecules (1 mole) = 22.4 L – This is true of ANY gas! – How many liters are in 12.3 moles of H2SO4 (gas) at STP? 12.3 moles H2SO4 22.4 Liters 1 mole H2SO4 = 276 liters H2SO4 Mole Road Map Example • What volume is occupied by 90 g CO2 at STP? • 1. Determine conversion factors • 2. Use factor label 1 mole CO2 = 44 g CO2 1 mole CO2 (at STP) = 22.4 L CO2 90 g CO2 1 mole CO2 22. 4 L CO2 44 g CO2 1 mole CO2 = 45.8 L CO2 HAPPY VALENTINE’S DAY • Make a poem!!! ROSES ARE RED VIOLETS ARE BLUE MOLAR MASS SURE IS SWEET AND MOLAR VOLUME IS TOO MOLE MOVIE • http://www.learner.org/resources/series61.ht ml# BELLWORK 2-16 • Convert 3.49 x 1029 ions of PbCl2 to moles. • What is the mass of hydrogen in 50.0 grams of C3H8? PERCENT COMPOSITION • Relative amounts of elements in a compound are expressed as PERCENT COMPOSITION. % composition steps • Step 1: Find the total mass of the compound • Step 2: Divide the total mass of each element by the total mass of the compound • Step 3: Multiply by 100 Example • K2CrO4 • Total mass = 2 K (39.1 x 2) + Cr (52) + 4 O (16 x 4) 194.2 g • K: 78.2 g/ 194.2 g = .403 x 100 = 40.3% K • Cr: 52 g/ 194.2 g = .268 x 100 = 26.8 % Cr • O: 64 g/ 194.2 g = .329 x 100 = 32.9 % O 32.9 % + 26.8 % + 40.3% = 100% CAFFEINE: C8H10N4O2 ELEMENT Carbon 12(8)= 96 grams 96/194= .4948 x100 Hydrogen 1(10)= 10 grams 10/194= .052 x100 Nitrogen 14(4)= 56 grams 56/194= .289 x100 Oxygen 16(2)= 32 grams 32/194= .165 x100 PERCENT COMPOSITION 49.5% 5.2% 28.9% 16.5% EMPIRICAL FORMULAS • The lowest whole-number ratio of the atoms of the elements in a compound • Is C2O4 an empirical formula? • CO2 1:2 ratio between Carbon and Oxygen • Is H2SO4 an empirical formula? – Yes, because you can’t reduce the subscripts any further. (2:1: 4 ratio) • A compound is analyzed and found to contain 25.9% nitrogen and 74.1% oxygen. What is the empirical formula of the compound? STEPS FOR EMPIRICAL FORMULA PROBLEMS • sTeP 1: change all percents of elements to grams • sTeP 2: divide grams of each element by molar mass of each element- this will give you moles of each element • sTep 3: divide moles of each element by the smallest amount of moles • sTeP 4: if the ratios are not in whole numbers multiply each by the smallest whole number that will convert both subscripts to whole numbers Example Problem • Step 1: 25.9 grams of Nitrogen 74.1 grams of Oxygen • Step 2: 25.9 g x 1 mol = 1.85 mol N 14 g 74.1 g x 1mol = 4.63 mol O 16 g • Step 3: 1.85 mol N/ 1.85 = 1 mol N 4.63 mol O/ 1.85 = 2.5 mol O • Step 4: multiply mol N and mol O by 2 to get whole numbers: 2 mol N and 5 mol O • Empirical formula equals N2O5 Class work • What is the empirical formula of a compound that is 52.5% Phosphorus and 47.5% Oxygen? • What is the empirical formula of a compound that is 10.0% C, .80% H, and 89.1% Cl? • What is the empirical formula of a compound that is 7.8% C and 92.2% Cl? Did you get these answers? • P4O7 • CHCl3 • CCl4 Bellwork 2/20 • #1: Which of the following can be classified as an empirical formula? a) SCl2 b) C6H10O4 c) Na2SO3 • #2: What is the empirical formula of a compound that is 60.0 % Magnesium and 40.0% oxygen? SOLUTION • #1: a and c are empirical formulas • #2: Change % to grams • 60.0% Magnesium= 60.0 g Magnesium • 40.0 % Oxygen = 40.0 g Oxygen • 2. Convert the grams of each element to moles (using the molar mass) 60.0 g Magnesium 1 mole Magnesium 24.3 g Magnesium = 2.46 moles Magnesium Solution Continued • Oxygen: 40.0 g Oxygen 1 mole Oxygen 16.0 g Oxygen = 2.50 moles Oxygen Solution Continued • 3. Now divide the number of moles for each element by the smallest number of moles. • 2.46 moles Magnesium • 2.50 moles Oxygen • Magnesium has the smallest number of moles {2.46 moles} • So divide the number of moles of Magnesium and Oxygen by 2.46 Solution Continued • Magnesium = 2.46 moles / 2.46 moles = 1 Mg • Oxygen = 2.50 moles / 2.46 moles = 1.02 O • Mg1O1 •MgO is the empirical formula MOLECULAR FORMULAS • Is a simple whole-number multiple of the empirical formula – Can be the same as its experimentally determined empirical formula. – EXAMPLE: C8H16 is the molecular formula CH2 would be the empirical formula STEPS FOR FINDING MOLECULAR FORMULA • Step 1: First find the empirical formula following the steps given previously (sometimes it may be given to you) • Step 2: Divide molar mass of compound by empirical formula mass. • Step 3: Multiply each subscript in the empirical formula by the value you got in step 2. • The molar mass of a a compound is 90 g/mol. The empirical formula is CH2O. What is the molecular formula? • Solution: 90/30= 3 – Therefore, molecular formula = C3H6O3 First Previous Next Last List of Slides Notes Text Slide 12 of 26 • What is the molecular formula of the compound if the empirical formula is CO2 and the molecular mass is 132 g? • Nicotine, a component of tobacco, has an empirical formula of C5H7N. The molar mass of nicotine is 162 g. What is its molecular formula? • A compound contain 64.9% C, 13.5% H, and 21.6% O. Its molecular mass is 74 g. Find the molecular formula. • What is the molecular formula of a compound with an empirical formula of CH4N and molecular mass of 60? • The molar mass of CH4N is 30 g. • The molecular mass is 60 g. • Thus, molecular mass of CH4N / empirical gfm • 60 g / 30 g • =2 • You need to multiply each atom in the empirical by a factor “2” • Thus CH4N becomes C2H8N2 • C2H8N2 is the molecular formula HYDRATES • Hydrates are compounds that contain weakly bound water molecules as part of its crystal structure. – Appear dry • The water is not actually part of the chemical substance and this is reflected in the way the formula is written. – BaCl2 . 2 H2O The Nomeclature of Hydrates • Example: CuSO4 . 5 H2O – copper(II) sulfate pentahydrate Try These • Na2SO4 .10H2O – Sodium sulfate decahydrate • Calcium chloride dihydrate – CaCl2 . 2H2O Finding the Empirical Formula Hydrate Style • Example #1: A hydrate of magnesium iodide has a formula MgI2. X H2O. A 1.055 g sample is heated to a constant value of 0.695 g. What is the value of X? • Step 1: Determine from problem the grams of H2O and grams of compound (MgI2) – MgI2 = .695 g – H2O = .36 g SOLUTION • Step 2: Calculate the number of moles of MgI2 in the final sample: – Moles MgI2 = .695 g/ (278.1 g/mol) = .0025 moles • Calculate the number of moles of H2O in the sample using the molar mass of H2O = 18.02, and the mass of the evaporated H2O = 0.36 g. – Moles H2O = .36 g/ (18.02 g/mol) = .020 moles • Step 3: Divide by the lowest number of moles (will always be moles of compound, not water) .02/.0025 = 8 .0025/.0025 = 1 And the molecular formula is: MgI2 . 8 H2O Hydrate Problems • Practice Problems Application of Hydrates? • Methane Hydrate could potentially be a new energy source. If only one percent of the methane hydrate resource could be made technically and economically recoverable, the United States could more than double its domestic natural gas resource. Global Climate Hazard • If global warming occurs, the temperature will rise and decompose some of these methane hydrates in the earth. Methane is one of the most harmful greenhouse gases and this effect could be potentially threatening. Electronic Equipment? • Cameras made in Japan are often shipped to America by ships • A calcium chloride hydrate is often packaged with the camera in the box to absorb moisture so the camera won’t be damaged. Bellwork 2/22 • You have a 35.64 g sample of hydrated barium bromide. The sample is heated to drive off the water. The dry sample has a mass of 30.42 g of barium bromide. What is the formula for the hydrate? ANSWER TO BELLWORK 2/22 • BaBr2 * 3H2O Warm-Up 10-23 • Propane is a gas used for cooking and heating. How many atoms are in 2.12 moles of propane? (Propane = C3H8) • What is the percent composition of C and H in propane? – 1.40 x 1025 atoms Warm-Up 10-24 • Calculate the mass of 7.89 x 1020 atoms of iron (Fe). Warm-Up 10-25-06 • What is the molar mass of NaHCO3? • How many moles is .346 grams of H2SO4? • 12.89 moles of Potassium Chloride equals how many formula units of Potassium Chloride?