Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Mass Relationships By Doba Jackson, Ph.D. Copyright © 2010 Pearson Prentice Hall, Inc.

Balancing Chemical Equations Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Balancing Chemical Equations A balanced chemical equation shows that the law of conservation of mass is adhered to. In a balanced chemical equation, the numbers and kinds of atoms on both sides of the reaction arrow are identical. 2NaCl(s) 2Na(s) + Cl2(g) A chemical reaction can be thought of as a rearrangement of the atoms to form new compounds. left side: 2 Na 2 Cl right side: 2 Na 2 Cl Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Symbols on a Different Level Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Symbols on a Different Level 2H2O(l) 2H2(g) + O2(g) microscopic: 2 molecules of hydrogen gas react with 1 molecule of oxygen gas to yield 2 molecules of liquid water. Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Symbols on a Different Level Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Symbols on a Different Level 2H2O(l) 2H2(g) + O2(g) microscopic: 2 molecules of hydrogen gas react with 1 molecule of oxygen gas to yield 2 molecules of liquid water. macroscopic: 0.56 kg of hydrogen gas react with 4.44 kg of oxygen gas to yield 5.00 kg of liquid water. Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Arithmetic: Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Arithmetic: Stoichiometry How many grams of each reactant is needed and how many grams of the product are expected? Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Arithmetic: Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Arithmetic: Stoichiometry Molecular Mass: Sum of atomic masses of all atoms in a molecule. Formula Mass: Sum of atomic masses of all atoms in a formula unit of any compound, molecular or ionic. C2H4: 2(12.0 amu) + 4(1.0 amu) = 28.0 amu HCl: 1.0 amu + 35.5 amu = 36.5 amu Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Arithmetic: Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Arithmetic: Stoichiometry One mole of any substance is equivalent to its molecular or formula mass. 1 mole = 28.0 g C2H4: 6.022 x 1023 molecules = 28.0 g 1 mole = 36.5 g 6.022 x 1023 molecules = 36.5 g HCl: Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Arithmetic: Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Arithmetic: Stoichiometry How many moles of chlorine gas, Cl2, are in 25.0 g? 25.0 g Cl2 1 mol Cl2 x = 0.353 mol Cl2 70.9 g Cl2 Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Arithmetic: Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Arithmetic: Stoichiometry How many grams of sodium hypochlorite, NaOCl, are in 0.705 mol? 0.705 mol NaOCl 74.5 g NaOCl x = 52.5 g NaOCl 1 mol NaOCl Na = 22.99 amu O = 15.99 amu Cl = 35.45 amu Copyright © 2010 Pearson Prentice Hall, Inc.

Law of Constant Composition Chemical Formula 2Hg 2HgO O2 + Chemical Equation HgO Joseph Priestly isolated oxygen in 1774 by heating mercury(II) oxide. Mass percentage of mercury Mass percentage of oxygen

Empirical and Molecular Formula’s Mass percentage of mercury Mass percentage of oxygen HgO contains one mole of Hg per mole of oxygen Empirical formula- a formula that shows the ratio of each element repective to each other. Does not always represent the actual formula.

Analysis of a 12.04-g sample of a liquid compound composed of carbon, hydrogen, and nitrogen showed it contain 7.34 g C, 1.85 g H, and 2.85 g N. What is the percent composition of this compound?

Aspirin is a compound with the molecular formula C9H8O4 Aspirin is a compound with the molecular formula C9H8O4. What is the percent composition of each element ?

Determining Empirical formula’s

A sample of the black mineral hematite, an oxide of iron found in many iron ores, contains 34.97 g of iron and 15.03 g of oxygen. What is the empirical formula of hematite?

What is the empirical formula of a compound if a sample contains 0 What is the empirical formula of a compound if a sample contains 0.130 g of nitrogen and 0.370 g of oxygen?

Concentrations of Reactants in Solution: Molarity Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Concentrations of Reactants in Solution: Molarity Molarity (M): The number of moles of a substance dissolved in each liter of solution. In practice, a solution of known molarity is prepared by weighing an appropriate amount of solute, placing it in a container called a volumetric flask, and adding enough solvent until an accurately calibrated final volume is reached. Solution: A homogeneous mixture. Solute: The dissolved substance in a solution. Solvent: The major component in a solution. It’s the volume of solution that’s needed and not simply the volume of water (assuming water is the solvent). Copyright © 2010 Pearson Prentice Hall, Inc.

Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Copyright © 2010 Pearson Prentice Hall, Inc.

Concentrations of Reactants in Solution: Molarity Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Concentrations of Reactants in Solution: Molarity Molarity converts between mole of solute and liters of solution: Moles of solute Liters of solution Molarity = 1.00 mol of sodium chloride placed in enough water to make 1.00 L of solution would have a concentration equal to: 1.00 mol mol = 1.00 or 1.00 M 1.00 L L Copyright © 2010 Pearson Prentice Hall, Inc.

Concentrations of Reactants in Solution: Molarity Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Concentrations of Reactants in Solution: Molarity How many grams of solute would you use to prepare 1.50 L of 0.250 M glucose, C6H12O6? Molar mass C6H12O6 = 180.0 g/mol 1.50 L 0.250 mol x = 0.275 mol 1 L 0.275 mol 180.0 g x = 49.5 g 1 mol Copyright © 2010 Pearson Prentice Hall, Inc.

Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Copyright © 2010 Pearson Prentice Hall, Inc.

Diluting Concentrated Solutions Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Diluting Concentrated Solutions dilute solution concentrated solution + solvent initial final Mi x Vi = Mf x Vf Since the number of moles of solute remains constant, all that changes is the volume of solution by adding more solvent. Molarity x Volume (in liters) = moles Since the conversion between liters and milliliters is multiplicative, the volume units do not have to be liters. All that is necessary is that the volume units are the same. Copyright © 2010 Pearson Prentice Hall, Inc.

Diluting Concentrated Solutions Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Diluting Concentrated Solutions Sulfuric acid is normally purchased at a concentration of 18.0 M. How would you prepare 250.0 mL of 0.500 M aqueous H2SO4? Mi = 18.0 M Mf = 0.500 M Vi = ? mL Vf = 250.0 mL Add acid to water! Mi Mf Vf 0.500 M 250.0 mL Vi = x = x = 6.94 mL 18.0 M Add 6.94 mL 18.0 M sulfuric acid to enough water to make 250.0 mL of 0.500 M solution. Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Arithmetic: Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Arithmetic: Stoichiometry Stoichiometry: The relative proportions in which elements form compounds or in which substances react. aA + bB cC + dD Grams of A Moles of A Moles of B Grams of B Definition from the Oxford Dictionary of Chemistry, Oxford University Press, 2000. Its origin is Greek for “element” “measure.” “grams-to-moles-to-moles-to-grams” You need the coefficients from the balanced chemical equation. You can relate any of the substances in the chemical equation to each other. Molar Mass of A Mole Ratio Between A and B (Coefficients) Molar Mass of B Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Arithmetic: Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Arithmetic: Stoichiometry Aqueous solutions of sodium hypochlorite (NaOCl), best known as household bleach, are prepared by reaction of sodium hydroxide with chlorine gas: 2NaOH(aq) + Cl2(g) NaOCl(aq) + NaCl(aq) + H2O(l) How many grams of NaOH are needed to react with 25.0 g Cl2? Grams of Cl2 Moles of Cl2 Moles of NaOH Grams of NaOH Molar Mass Mole Ratio Molar Mass Copyright © 2010 Pearson Prentice Hall, Inc.

Chemical Arithmetic: Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Chemical Arithmetic: Stoichiometry Aqueous solutions of sodium hypochlorite (NaOCl), best known as household bleach, are prepared by reaction of sodium hydroxide with chlorine gas: 2NaOH(aq) + Cl2(g) NaOCl(aq) + NaCl(aq) + H2O(l) How many grams of NaOH are needed to react with 25.0 g Cl2? 25.0 g Cl2 Remind students about significant figures. 1 mol Cl2 2 mol NaOH 40.0 g NaOH x x x 70.9 g Cl2 1 mol Cl2 1 mol NaOH = 28.2 g NaOH Copyright © 2010 Pearson Prentice Hall, Inc.

Yields of Chemical Reactions Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Yields of Chemical Reactions Actual Yield: Theoretical Yield: The amount actually formed in a reaction. The amount predicted by calculations. Actual yield of product Theoretical yield of product Percent Yield = x 100% Maximum percent yield is 100%. Copyright © 2010 Pearson Prentice Hall, Inc.

Reactions with Limiting Amounts of Reactants Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Reactions with Limiting Amounts of Reactants Limiting Reactant: The reactant that is present in limiting amount. The extent to which a chemical reaction takes place depends on the limiting reactant. Excess Reactant: Any of the other reactants still present after determination of the limiting reactant. C2H4O(aq) + H2O(l) C2H6O2(l) Copyright © 2010 Pearson Prentice Hall, Inc.

Reactions with Limiting Amounts of Reactants Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Reactions with Limiting Amounts of Reactants At a high temperature, ethylene oxide reacts with water to form ethylene glycol, which is an automobile antifreeze and a starting material in the preparation of polyester polymers: C2H4O(aq) + H2O(l) C2H6O2(l) Copyright © 2010 Pearson Prentice Hall, Inc.

Problem: Reactions with Limiting Amounts of Reactants Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Problem: Reactions with Limiting Amounts of Reactants Lithium oxide is used aboard the space shuttle to remove water from the air supply according to the equation: Li2O(s) + H2O(g) 2LiOH(s) If 80.0 g of water are to be removed and 65.0 g of Li2O are available, which reactant is limiting? How many grams of excess reactant remain? How many grams of LiOH are produced? Copyright © 2010 Pearson Prentice Hall, Inc.

Reactions with Limiting Amounts of Reactants Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Reactions with Limiting Amounts of Reactants Li2O(s) + H2O(g) 2LiOH(s) Which reactant is limiting? Amount of H2O that will react with 65.0 g Li2O: 65.0 g Li2O 1 mol Li2O 1 mol H2O x x = 2.17 moles H2O 29.9 g Li2O 1 mol Li2O Amount of H2O given: 80.0 g H2O 1 mol H2O x = 4.44 moles H2O 18.0 g H2O Li2O is limiting Copyright © 2010 Pearson Prentice Hall, Inc.

Reactions with Limiting Amounts of Reactants Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Reactions with Limiting Amounts of Reactants Li2O(s) + H2O(g) 2LiOH(s) How many grams of excess H2O remain? 2.17 mol H2O 18.0 g H2O x = 39.1 g H2O (consumed) 1 mol H2O 80.0 g H2O - 39.1 g H2O = 40.9 g H2O initial consumed remaining Copyright © 2010 Pearson Prentice Hall, Inc.

Reactions with Limiting Amounts of Reactants Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Reactions with Limiting Amounts of Reactants Li2O(s) + H2O(g) 2LiOH(s) How many grams of LiOH are produced? 2.17 mol H2O 2 mol LiOH 23.9 g LiOH x x = 104 g LiOH 1 mol H2O 1 mol LiOH Copyright © 2010 Pearson Prentice Hall, Inc.

Solution Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Solution Stoichiometry aA + bB cC + dD Volume of Solution of A Moles of A Moles of B Volume of Solution of B Molarity of A Mole Ratio Between A and B (Coefficients) Molar Mass of B These problems still come back to moles. Copyright © 2010 Pearson Prentice Hall, Inc.

Solution Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Solution Stoichiometry What volume of 0.250 M H2SO4 is needed to react with 50.0 mL of 0.100 M NaOH? H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l) Volume of Solution of H2SO4 Moles of H2SO4 Moles of NaOH Volume of Solution of NaOH Note that the method is very similar to that for mass stoichiometry. Molarity of H2SO4 Mole Ratio Between H2SO4 and NaOH Molarity of NaOH Copyright © 2010 Pearson Prentice Hall, Inc.

Solution Stoichiometry Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Solution Stoichiometry H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l) Moles of NaOH available: 50.0 mL NaOH 0.100 mol 1 L x x = 0.00500 mol NaOH 1 L 1000 mL Volume of H2SO4 needed: 0.00500 mol NaOH 1 mol H2SO4 1 L solution 1000 mL x x x 2 mol NaOH 0.250 mol H2SO4 1 L 10.0 mL solution (0.250 M H2SO4) Copyright © 2010 Pearson Prentice Hall, Inc.

Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Titration Titration: A procedure for determining the concentration of a solution by allowing a carefully measured volume to react with a solution of another substance (the standard solution) whose concentration is known. HCl(aq) + NaOH(aq) NaCl(aq) + 2H2O(l) Once the reaction is complete you can calculate the concentration of the unknown solution. How can you tell when the reaction is complete? Copyright © 2010 Pearson Prentice Hall, Inc.

Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Titration standard solution (known concentration) buret Erlenmeyer flask unknown concentration solution An indicator is added which changes color once the reaction is complete Copyright © 2010 Pearson Prentice Hall, Inc.

Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Phenolphthalein is commonly used for HCl-NaOH titrations. It turns red (pink) in slightly basic solutions. Copyright © 2010 Pearson Prentice Hall, Inc.

Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Titration 48.6 mL of a 0.100 M NaOH solution is needed to react with 20.0 mL of an unknown HCl concentration. What is the concentration of the HCl solution? HCl(aq) + NaOH(aq) NaCl(aq) + 2H2O(l) Volume of Solution of NaOH Moles of NaOH Moles of HCl Volume of Solution of HCl Molarity of NaOH Mole Ratio Between NaOH and HCl Molarity of HCl Copyright © 2010 Pearson Prentice Hall, Inc.

Chapter 6: Mass Relationships in Chemical Reactions 9/12/2018 Titration HCl(aq) + NaOH(aq) NaCl(aq) + 2H2O(l) Moles of NaOH available: 48.6 mL NaOH 0.100 mol 1 L x x = 0.00486 mol NaOH 1 L 1000 mL Moles of HCl reacted: 0.00486 mol NaOH 1 mol HCl x = 0.00486 mol HCl 1 mol NaOH Concentration of HCl solution: 0.00486 mol HCl 1000 mL x = 0.243 M HCl 20.0 mL solution 1 L Copyright © 2010 Pearson Prentice Hall, Inc.

Problem: What is the molecular mass of table sugar (sucrose, C12H22O11), and what is its molar mass in g/mol?

Problem: How many moles of sucrose are in a tablespoon of sugar containing 2.85 g?

Problem: How many grams are in 0 Problem: How many grams are in 0.0626 mol of NaHCO3, the main ingredient of Alka-Seltzer tablets?

Problem: Aqueous solutions of sodium hypochlorite (NaOCl, household bleach) are prepared by reaction of sodium hydroxide with chlorine. How many grams of NaOH are needed to react with 25.0 g of Cl2?

Problem: Cisplatin, an anticancer agent used for the treatment of solid tumors, is prepared by the reaction of ammonia with potassium tetrachloroplatinate. Assume that 10.0 g of K2PtCl4 and 10.0 g of NH3 are allowed to react.       (a) Which reactant is limiting, and which is in excess? (b) How many grams of the excess reactant are consumed, and how many grams remain? (c) How many grams of cisplatin are formed?