Warm-up If aluminum cans weigh 20.g each, how many cans are in a 150 kg truckload of cans? (solve using conversion factors) 1
THE MOLE 2
Measuring Matter How do chemists determine amounts of chemicals that react? C + O 2 CO 2 How much oxygen will react with 200. g of C? 3
Measuring Matter C + O 2 CO 2 1 atom of C 1 molecule of O 2 Atoms and molecules react particle-by-particle, not by mass. THUS: need to count particles!! 4
Counting GEDANKEN: How would you count a pail of pennies or a beaker of beans? 5
Counting by Mass Recycling centers do it all the time! If aluminum cans weigh 20.g each, how many cans are in a 150 kg truckload of cans? 150 kg 1 x 1000 g kg 1can x = 7500 cans 20 g 6
The Mole Chemists count atoms & molecules using the mole. 1 mole = 6.02 x 10 23 particles = Avogadro s number 7
Where did Avogadro stay when he was on vacation? A Mole-tel 8
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The Mole 1 mole = 6.02 x 10 23 particles 602 000 000 000 000 000 000 000. 1 mole = # grains of sand on all the earth s beaches! 10
The Mole: Chemists Dozen The mole is a number, just like dozen is a number 11
The Mole Why use such a huge number for counting atoms and molecules? What does a mole look like? Sulfur Lead Water 12
The Mole Abbreviation? mol 1 mole = 6.02 x 10 23 particles particle atom ion molecule atom ion mlc formula unit 13 fu
Representative Particle Substance Particle atomic nitrogen atom N nitrogen (gas) molecule N 2 water molecule H 2 O sodium ion ion Na + calcium fluoride formula unit CaF 2 14
1 mole = 6.02 x 10 23 particles The Mole I ll do 2 problems. 1. How many molecules in 1.14 mol SO 3? 2. How many moles in 1.86 x 10 24 mlc SO 3? 15
Calculating Atoms Some problems have an extra step, requiring the number of atoms in one molecule. Example: In one molecule of H 2 O, there are three atoms, one O and 2H. 1 mlc H 2 O = 3 atoms = 1 atom O = 2 atom H 16
Calculating Atoms How many atoms are in 1.52 mol H 2 O? 1.52 mol 1 x 6.02x1023 mlc 1 mol x 3 atom 1 mlc = 2.75 x 10 24 atom 17
Gram Atomic Mass (GAM) GAM = atomic mass expressed in grams rather than atomic mass units (u). Atomic mass of carbon is 12.011 u so, GAM of carbon = 12.011 g 18
Gram Atomic Mass How many atoms are there in one GAM of C? Recall: 1 u = 1.66 x 10-24 g 12.0 g C 1 1 u x 1.66 x 10-24 g x 1 atom C 12.0 u = 6.02 x 10 23 atoms C Try it for a GAM of sulfur. 19
Gram Atomic Mass How many atoms are there in 1 GAM of any element? (count by mass) 20
The Mole Carbon: 1 mole = 12.0 g = 6.02 x 10 23 atom Iron: 1 mole = 55.8 g = 6.02 x 10 23 atom http://www.youtube.com/watch?v=tel4jeetvmg 21
Be Careful with Units The mass of one carbon atom is 12.0 u (atomic mass units) 1 atom =12.0 u 1 mole = 12.0 g The mass of one mole of carbon atoms is 12.0 g. 22
Compounds What is the mass of one mole of a compound? Just add up the GAM s of the atoms. Let s use H 2 O as an example. 23
GMM of Water: H 2 O H O + H + H = O 16.0 g + 1.0 g + 1.0 g = 18.0 g per mol gram molecular mass H 24
Gram Molecular Mass Thus for water 1 mole = 18.0 g = 6.02 x 10 23 molecules 25
Gram Molecular Mass Calculate the GMM for: N 2 O 5 26
What about Ionic Compounds? Calculate the GFM for: (gram formula mass) (NH 4 ) 2 SO 4 27
Terms GAM GMM Molar Mass GFM (the mass of one mole) 28
Conversion Factors particle 6.02 x10 23 part. = 1 mol mole mass molar mass (g) = 1 mol look it up 29
Sample Problems 1. How many molecules are in 3.0 moles of CO 2? 2. How many moles is 81 g of H 2 O? 30
Molar Volume of a Gas Unlike solids and liquids, the volume of 1 mole of any gas at STP is 22.4 L. STP on Table A 1 mol = 22.4 L (gas at STP) (see box) 31
Molar Volume of a Gas 1 mol = 22.4 L (gas at STP) How many moles are there in 6.2 L of NO 2 at STP? 32
Gas Density (Gas density measured in g/l) The density of an unknown gas is 2.87 g/l at STP. What is its molar mass? 2.87 g L x 22.4 L mol 64.3 = mol g 33
Gas Density Try it: What is the density of krypton gas at STP? 34
Mole Road Map particle 6.02 x10 23 part. = 1 mol mole volume 22.4 L = 1 mol (Gas at STP) mass molar mass (g) = 1 mol look it up 35
I ll do one, then it s your turn! 36
Chemical Formula Subscripts H 2 O 2 atoms 1 atom Ratio of 2 atoms H to 1 atom O = 20 atoms H to 10 atoms O = 2 mol H to 1 mol O Always a ratio of 2:1 Not a ratio of masses! 37
Empirical Formulas Lowest whole number ratio of atoms in a compound. Molec. Form. Empirical Form. H 2 O H 2 O N 2 H 4 NH 2 And all ionic compounds 38
Percent Composition (means % by mass of each element in a compound) What is the % (by mass) of each element in carbon dioxide (CO 2 )? First determine molar mass: C: 1 x 12.0 g = 12.0 g O: 2 x 16.0 g = 32.0 g total = 44.0 g per mol 39
Percent Composition CO 2 Then determine % composition: 12g %C = x 100% = 27% C 44g %O = x 100% = 73% O 32g 44g 40
Percent Composition 1. What is the % nitrogen in ammonium chloride? 2. What is the mass of nitrogen in 152 g of ammonium chloride? 41
Chemical Formulas Can be determined from the percent composition of each element in the compound. What is the formula of a compound with 25.9% N and 74.1% O? 42
Solve: 25.9% N and 74.1% O Assume 100 g of compound thus 25.9 g N and 74.1 g O The chemical formula is NOT: N 25.9 O 74.1 Percents or masses are not subscripts. 43
Chemical Formula Must find the ratio of moles 1 mol 25.9 g N x = 1.85 mol N 14.0 g 74.1 g O x 1 mol = 4.63 mol O 16.0 g 44
Chemical Formula N: 25.9 % O: 74.1 % 25.9 g 74.1 g 1.85 mol 4.63 mol N 1.85 O 4.63 1.85 1.85 N 1 O 2.5 N 2 O 5 45
Chemical Formula You Try It! What is the formula of a compound that is 36% calcium and 64% chlorine? 46
Empirical Formula Actually, the formula you get using % composition is an empirical formula, not a molecular formula. Prove it to yourself: a. What is the percent composition of C 2 H 8 N 2? b. Given your answer in part a, calculate the chemical formula. 47
How to Get Molecular Formula Molecular formula was C 2 H 8 N 2 Empirical formula was CH 4 N What one more piece of information is needed to know the molecular formula is C 2 H 8 N 2? Molar mass of the compound! 48
Molecular Formula Can be determined from empirical formula and molar mass. What is molecular formula of a compound with empirical formula of CH 4 N and molar mass of 60 g? 49
Molecular Formula Empirical Mass of CH 4 N: C: 1 x 12.0 = 12.0g H: 4 x 1.0 = 4.0 g N: 1 x 14.0 = 14.0 g total = 30.0 g vs. molar mass of 60 g. Off by factor of 2. compare Thus molecular formula = C 2 H 8 N 2 50
You Try One! What is the empirical formula of a compound that is 71.4% Br and 28.6% O? What is its molecular formula if this compound has a molar mass of 224g? 51
Summary of Calculations 1. Road Map (let units help!) (diagram in problem set) 1 mol = 6.02 x 10 23 particles 1 mol = molar mass (g) 1 mol = 22.4 L (gas at STP) 52
Summary of Calculations 2. % Composition (by mass): start with formula molar mass calc. divide mass of each element by molar mass (x 100) 53
Summary of Calculations 3. Empirical Formula: start with % comp. change % sign to grams convert grams to moles moles as subscripts divide by smallest number 54
Summary of Calculations 4. Molecular Formula: divide molar mass by empirical formula molar mass multiply all subscripts by this result 55
Hocus pocus Abracadabra I command my homework to do itself. BE DONE! Flip aaflip aaaaaflip Rats 56
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Warm-up What is Avogadro s number? What is it used for? 58
Warm-up What is Avogadro s number? How many moles is 6.78 x 10 25 molecules of carbon dioxide? 59
Warm-up How many iron atoms are there in one GAM of iron? 60
Warm-up What did Avogadro put on tacos? How many oxygen atoms are in 3.5 mol sodium carbonate? What is GFM of sodium carbonate? How many formula units are in 0.51g of sodium carbonate? (use the map in the problem set) 61
Warm-up How many moles are 4.2E25 fu of sodium carbonate? How many oxygen atoms are in 3.5 mol sodium carbonate? 62
Warm-up How many moles of CO are 2 9.45 x 10 24 molecules of CO? 2 What is GMM of N O? 2 What did Avogadro put on tacos? 63
Warm-up What is GMM of N 2 O? What is GFM of aluminum sulfate? 64
Warm-up How many molecules are in 0.381 L of carbon dioxide? What is the percent of oxygen in sulfuric acid? Honors: What is the density of Xenon gas at STP? 65
Warm-up How many molecules are in 0.381 L of carbon dioxide? What is the volume of 27.8 g of carbon dioxide at STP? What is the percent of oxygen in sulfuric acid? 66
Warm-up You are at Burger King with a friend. She picks up a 0.51g salt packet for her fries and asks What is this stuff and how many thingies are in this packet? What is your answer? Of course you know thingies are formula units since NaCl is an ionic compound. 67
Warm-up You are at Burger King with a friend. She picks up a 0.51g salt packet for her fries and asks What is this stuff and how many thingies are in this packet? What is your answer? What is the volume (@STP) of 8.43 x 10 25 molecules of SO 2? 68
Warm-up What is the volume of 18.5 g of SO 2 at STP? What is the percent of oxygen in barium hydroxide? What is the formula of a compound that is 27.3% carbon & 72.7% oxygen? 69
Warm-up How many grams is 9.3 x 10 24 fu of calcium nitrate? What is the percent of copper in copper(i) oxide? A compound is 87.5% N and 12.5% H. What is its empirical formula? 70
Warm-up How many grams is 9.3 x 10 24 fu of calcium nitrate? A compound is 87.5% N and 12.5% H. What is its empirical formula? If its molar mass is 64 g/mol, what is its molecular formula? 71
Warm-up In a lab experiment, it is found that 0.22 g S reacts with 0.33 g O. What is the mole ratio of oxygen to sulfur? What is the empirical formula of the compound that formed? 72
Lab 9 Empirical Formula Empty crucible 12.53 g Crucible + Mg 12.90 g Crucible + Mg + O 13.11 g 1. mass Mg 3. mass O Conversion factors 2. mass Mg mol Mg 4. mass O mol O use 2 sig figs (0.022 mol) 5. Then ratio of mol Mg to mol O 73
Warm-up A compound is 87.5% N and 12.5% H. What is its empirical formula? If its molar mass is 32 g/mol, what is its molecular formula? What is the % composition of H 2 O? 74