Chapter 3 Stoichiometry

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1 Chapter 3 Sep 22 1:45 PM Average atomic mass: The weighted average of all isotopes of a specific element. Takes into consideration abundance of each isotope. (% x M 1 ) + (% x M 2 ) +... Sep 22 1:45 PM 1

2 Copper has two isotopes: 69.2% of all copper has a mass of 63 amus and 30.8% of all copper has a mass of 65 amus. What is copper's atomic mass? Notice which isotope the average atomic mass is closest to!!! Sep 22 1:45 PM Mass Spectroscopy: A separation technique used to separate substances in a mixture based on their mass. Oct 1 3:41 PM 2

3 Oct 1 3:41 PM Avogadro's Number: 6.022x10 23 particles in 1 mole Molar Mass: The addition of the atomic mass of each atom (go out to the hundredth place!) (Sand is just SiO 2 ) Oct 4 1:52 PM 3

4 Percent composition: Compares the mass of one element in 1 mole of a compound C 2 H 5 OH Molar mass = g/mol % comp of carbon: 2 carbons = 2 x = % comp = x 100 = 52.13% Oct 24 1:41 PM Calculate the mass percent for all of the elements present in Penicillin F. C 14 H 20 N 2 SO 4 Oct 24 2:06 PM 4

5 Empirical Formula: Chemical compound with the lowest whole number ratio. C 3 H 8 Molecular Formula: chemical compound with the same ratio as the empirical or a multiple of the empirical C 3 H 8, C 6 H 16 Oct 24 2:14 PM Let's say we know that a compound has the following Mass Percents: 71.65% Cl, 24.27% C, 4.07% H Oct 24 2:22 PM 5

6 A white powder is analyzed and found to contain 43.64% phosphorus and 56.36% oxygen by mass. The compound has a molar mass of g/mole. what are the compound's empirical and molecular formulas? Oct 24 2:38 PM Caffeine contains 49.48% carbon, 5.15% hydrogen, 28.87% nitrogen, and 16.49% oxygen by mass and has a molar mass of g/mole. determine the molecular formula for caffeine. Oct 24 3:05 PM 6

7 A sample of indium chloride weighing g is found to contain g of chlorine. What is the empirical formula of the indium compound? Rubbing alcohol was found to contain 60.0 % carbon, 13.4 % hydrogen. What is the empirical formula of rubbing alcohol? Oct 29 8:12 AM An unknown compound was found to have a percent composition as follows: 47.0 % potassium, 14.5 % carbon, and 38.5 % oxygen. What is its empirical formula? If the true molar mass of the compound is g/mol, what is its molecular formula? Oct 29 8:13 AM 7

8 What mass of oxygen will react with 96.1 grams of propane? C 3 H 8 + O 2 CO 2 + H 2 O 1. Balance the equation first C 3 H 8 + 5O 2 3CO 2 + 4H 2 O 2. Convert the grams of propane into moles 96.1 g C 3 H 8 1 mol C 3 H 8 = mol C 3 H g C 3 H 8 3. Convert the moles of Propane into moles oxygen mol C 3 H 8 5 mol O 2 = mol O 2 1 mol C 3 H 8 4. Convert the moles of Oxygen into grams of oxygen mol O g O 2 1 mol O 2 = g O 2 Oct 24 3:08 PM Solid Lithium Hydroxide is used in space vehicles to remove exhaled carbon dioxide from the living environments by forming solid lithium carbonate and liquid water. What mass of gaseous carbon dioxide can be absorbed by 1.00kg of lithium hydroxide? Oct 24 3:28 PM 8

9 Baking soda (sodium bicarbonate) is often used as an antacid. It neutralizes excess hydrochloric acid secreted by the stomach. Milk of Magnesia, which is an aqueous suspension of magnesium hydroxide, is also used as an antacid. Which is the more effective antacid per gram? Oct 24 3:32 PM Limiting Reactant: The reactant that is consumed first and that limits the amounts of products that can be formed Nitrogen gas can be prepared by passing gaseous ammonia over solid copper (II) oxide at high temperatures. the other products of the reaction are solid copper and water vapor. If a sample containing 18.1g of ammonia is reacted with 90.4 g of CuO, which is the limiting reactant? How many grams of N 2 will be formed. 2NH 3 + 3CuO N 2 + 3Cu + 3H 2 O 18.1g 90.4 g Oct 24 3:35 PM 9

10 2NH 3 + 3CuO N 2 + 3Cu + 3H 2 O 18.1g 90.4 g 28.01g N g NH 3 1 mol NH 3 1 mol N g NH 3 2 mol NH 3 1 mol N 2 = 14.90g N g CuO 1 mol CuO 79.55g CuO 1 mol N g N 2 3 mol CuO 1 mol N 2 = 10.61g N 2 Copper (II) oxide makes the smaller amount of Nitrogen, therefore copper (II) oxide is the limiting reagent and only 10.61g of Nitrogen gas is made Oct 24 3:42 PM Theoretical yield: The amount of product formed when the limiting reactant is completely consumed Percent Yield: The actual yield of product divided by the theoretical yield times 100 Oct 24 3:49 PM 10

11 A 50.6 g sample of Mg(OH) 2 is reacted with 45.0 g of HCl What is the theoretical yield of MgCl 2? Mg(OH) HCl > MgCl H 2 O 50.6 g Mg(OH) 2 1 mol Mg(OH) 2 1 mol MgCl g Mg(OH)2 1 mol Mg(OH)2 1 mol MgCl2 95.3g MgCl g MgCl g HCl 1 mol HCl 36.5 g HCl 1 mol MgCl g MgCl 2 2 mol HCl 1 mol MgCl g MgCl 2 If only grams of MgCl 2 is formed, what is the percent yield for this reaction? Oct 29 8:18 AM Dilutions: Adding water to decrease concentration M 1 V 1 = M 2 V 2 Concentration: A measurement of how much solute is dissolved in a specific solvent or solution Percent by mass = Mass of the solute mass of the solution x 100 Percent by volume = Molarity (M) = Molality (m) = Volume of the solute Volume of the solution x 100 moles of solute liters of solution moles of solute kg solvent Sep 22 9:47 AM 11

12 You are combining 8.40 grams of barium hydroxide with 50.0 ml of M hydrofluoric acid, how much barium fluoride will be formed? What is the concentration of the other product. Sep 22 9:57 AM Oct 1 3:39 PM 12

Chapter 9: Stoichiometry The Arithmetic ti Of Equations

Chapter 9: Stoichiometry The Arithmetic of Equations Chemical Calculations Limiting Reagent and Percent Yield The Arithmetic ti Of Equations -- The Arithmetic of Equations -- Using Everyday Equations Stoichiometry