Chapter 4: Reactions in Aqueous Solution Chemistry: McMurry and Fay, 6th Edition Chapter 3: Mass Relationships in Chemical Reactions 2/23/2019 5:59:27 AM Chapter 4: Reactions in Aqueous Solution Copyright © 2011 Pearson Prentice Hall, Inc.

4.1-4.2 Concentrations of Reactants in Solution: Molarity Chapter 3: Formulas, Equations, and Moles 2/23/2019 4.1-4.2 Concentrations of Reactants in Solution: Molarity Molarity: 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). Either pictures or showing a volumetric flask might be helpful.

Concentrations of Reactants in Solution: Molarity Chemistry: McMurry and Fay, 6th Edition Chapter 3: Mass Relationships in Chemical Reactions Concentrations of Reactants in Solution: Molarity 2/23/2019 5:59:27 AM Copyright © 2011 Pearson Prentice Hall, Inc.

Concentrations of Reactants in Solution: Molarity Chapter 3: Formulas, Equations, and Moles 2/23/2019 Concentrations of Reactants in Solution: Molarity Molarity converts between mole of solute and liters of solution: molarity = moles of solute liters of solution 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 © 2008 Pearson Prentice Hall, Inc.

Concentrations of Reactants in Solution: Molarity Chapter 3: Formulas, Equations, and Moles 2/23/2019 Concentrations of Reactants in Solution: Molarity What is the molarity of a solution made by dissolving 2.5 g of NaCl in enough water to make 125 ml of solution? How many grams of solute would you use to prepare 1.50 L of 0.250 M glucose, C6H12O6? Calculate the volume of a 0.80M potassium bromide solution containing 23.6 g of potassium bromide. Copyright © 2008 Pearson Prentice Hall, Inc.

Dilution

Diluting Concentrated Solutions Chapter 3: Formulas, Equations, and Moles 2/23/2019 Diluting Concentrated Solutions dilute solution concentrated solution + solvent initial final Mi Vi = Mf Vf Or M1V1 = M2V2 Since the number of moles of solute remains constant, all that changes is the volume of solution by adding more solvent. Copyright © 2008 Pearson Prentice Hall, Inc.

Diluting Concentrated Solutions Chapter 3: Formulas, Equations, and Moles 2/23/2019 Diluting Concentrated Solutions 1. 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? 2. To what volume should you dilute 0.200 L of a 15.0 M NaOH solution to obtain a 3.00 M NaOH solution? Add acid to water! Copyright © 2008 Pearson Prentice Hall, Inc.

4.8-4.9 Solution Stoichiometry Chapter 3: Formulas, Equations, and Moles 4.8-4.9 Solution Stoichiometry 2/23/2019 In aqueous reactions, quantities of reactants and products are often specified in terms of volume and concentrations. We can use the stoichiometric coefficients in the chemical equation to convert to the amount of another reactants of products in moles. aA + bB cC + dD Volume of Solution of A Moles of A Moles of B Volume of Solution of B These problems still come back to moles. Molarity of A Mole Ratio Between A and B (Coefficients) Molarity of B Dang Copyright © 2008 Pearson Prentice Hall, Inc.

Solution Stoichiometry Chapter 3: Formulas, Equations, and Moles Solution Stoichiometry 2/23/2019 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 NaOH Moles of NaOH Moles of H2SO4 Volume of Solution of H2SO4 Molarity of NaOH Molarity of H2SO4 Mole Ratio Between NaOH and H2SO4 Dang Copyright © 2008 Pearson Prentice Hall, Inc.

Example What volume of 0.150 M KCl is required to completely react with 0.150 L of 0.175 M Pb(NO3)2 in the reaction 2 KCl(aq) + Pb(NO3)2(aq)  PbCl2(s) + 2 KNO3(aq) Dang

Example What is the minimum amount (L) of 6.0 M H2SO4 necessary to produce 25.0 g of H2 . Assumed H2SO4 is limited 2 Al(s) + 3 H2SO4(aq)  Al2(SO4)3(aq) + 3 H2(g)

Titration The base solution is the titrant in the burette. As the base is added to the acid, the H+ reacts with the OH– to form water. But there is still excess acid present so the color does not change. At the titration’s endpoint, just enough base has been added to neutralize all the acid. At this point the indicator changes color. Dang

Example The titration of 10.00 mL of HCl solution of unknown concentration requires 12.54 mL of 0.100 M NaOH solution to reach the end point. What is the concentration of the unknown HCl solution? Dang

Examples A 30.00 mL sample of an unknown H3PO4 solution is titrated with a 0.100 M NaOH. The equivalence point is reached when 26.38 mL of NaOH solution is added. What is the concentration of the unknown H3PO4 solution? The neutralization reaction is H3PO4(aq) + 3 NaOH(aq)  3H2O(l) + Na3PO4(aq) Dang

Electrolytes and Nonelectrolytes materials that dissolve in water to form a solution that will conduct electricity are called electrolytes materials that dissolve in water to form a solution that will not conduct electricity are called nonelectrolytes

Electrolytes in Aqueous Solution Chapter 4: Reactions in Aqueous Solution 2/23/2019 Electrolytes in Aqueous Solution Strong Electrolytes: Compounds that dissociate to a large extent into ions when dissolved in water. KCl(aq) K1+(aq) + Cl1-(aq) Weak Electrolytes: Compounds that dissociate to a small extent into ions when dissolved in water. H1+(aq) + CH3CO21-(aq) CH3CO2H(aq) For a 0.10 M solution, KCl is approximately 98% dissociated while CH3CO2H (acetic acid) is a little more than 1% dissociated. The size of the arrows indicate which side of the chemical equation the equilibrium lies on. The use of the equilibrium arrows is minimal until later chapters on kinetics and chemical equilibrium. Nonelectrolytes: Substances which do not produce ions in aqueous solutions. H2O C12H22O11(aq) C12H22O11(s) Copyright © 2008 Pearson Prentice Hall, Inc.

Electrolytes in Aqueous Solution Hydroxides are also ionic compounds.

Conceptual question Three different substances, A2X, A2Y, and A2Z, are dissolved in water, with the following results. (Water molecules are omitted for clarity.) (a) Which of the substances is the strongest electrolyte, and which is the weakest? Explain. (b) What is the molar concentration of A ions and Y ions in a 0.350 M solution of A2Y? (c) What is the percent ionization of A2X indicated in the graphical representation?

Calculating the Concentration of Ions in a Solution at is the total molar concentration of ions in a 0.350 M solution of the strong electrolyte Na2SO4, assuming complete dissociation? What is the molar concentration of Br– ions in a 0.225 M aqueous solution of FeBr3, assuming complete dissociation?

Some Ways That Chemical Reactions Occur Chapter 4: Reactions in Aqueous Solution 2/23/2019 Some Ways That Chemical Reactions Occur Precipitation Reactions: Processes in which soluble reactants yield an insoluble solid product that falls out of solution. NaNO3(aq) + AgCl(s) AgNO3(aq) + NaCl(aq) Copyright © 2008 Pearson Prentice Hall, Inc.

Some Ways That Chemical Reactions Occur Acid-Base Neutralization Reactions: Processes in which an acid reacts with a base to yield water plus a salt. H2O(l) + NaCl(aq) HCl(aq) + NaOH(aq) Acid + Base  Water + Salt

Some Ways That Chemical Reactions Occur Chapter 4: Reactions in Aqueous Solution 2/23/2019 Some Ways That Chemical Reactions Occur Oxidation-Reduction (Redox) Reactions: Processes in which one or more electrons are transferred between reaction partners (atoms, molecules, or ions). MgCl2(aq) + H2(g) Mg(s) + 2HCl(aq) Element + Compound  Compound + Element Neutral state: (s), (l), (g) Copyright © 2008 Pearson Prentice Hall, Inc.

Precipitation Reactions and Solubility Guidelines Write the chemical formulas of the products (use proper ionic rules). CB + AD AB + CD double replacement reaction *Remember that metal cation does not bond to another metal cation

Aqueous Reactions and Net Ionic Equations Chapter 4: Reactions in Aqueous Solution 2/23/2019 Aqueous Reactions and Net Ionic Equations Molecular Equation: All substances in the chemical equation are written using their complete formulas as if they were molecules. NaNO3(aq) + AgCl(s) AgNO3(aq) + NaCl(aq) strong electrolytes indicated as (aq) soluble Precipitate insoluble Granted, all of the substances in the chemical equation are ionic compounds but it’s common to call this the molecular equation. Pictures are useful especially with this reaction. Solutions of lead(II) nitrate and potassium iodide are colorless while the precipitate of lead(II) iodide is yellow. Copyright © 2008 Pearson Prentice Hall, Inc.

Aqueous Reactions and Net Ionic Equations Chapter 4: Reactions in Aqueous Solution 2/23/2019 Aqueous Reactions and Net Ionic Equations Ionic Equation: All of the strong electrolytes are written as ions. AgNO3(aq) NaCl(aq) Ag2+(aq) + NO31- (aq) + Na1+(aq) + Cl1-(aq) Na1+(aq) + NO31- (aq) + AgCl(s) Note the proper charges (as learned previously when writing ionic compound formulas). NaNO3(aq) Copyright © 2008 Pearson Prentice Hall, Inc.

Aqueous Reactions and Net Ionic Equations Chapter 4: Reactions in Aqueous Solution 2/23/2019 Aqueous Reactions and Net Ionic Equations Spectator Ions: Ions that undergo no change during the reaction and appear on both sides of the reaction arrow. Ag2+(aq) + NO31- (aq) + Na1+(aq) + Cl1-(aq) Na1+(aq) + NO31- (aq) + AgCl(s) Copyright © 2008 Pearson Prentice Hall, Inc.

Aqueous Reactions and Net Ionic Equations Chapter 4: Reactions in Aqueous Solution 2/23/2019 Aqueous Reactions and Net Ionic Equations Net Ionic Equation: Only the ions undergoing change are shown. AgCl2(s) Ag+(aq) + Cl1-(aq) This doesn’t suggest that you can actually have a solution of iodide ion. The corresponding cations and anions are present but they are spectator ions. An aqueous solution that contains lead(II) ion when mixed with another one that contains iodide ion will typically produce a precipitate of lead(II) iodide. Copyright © 2008 Pearson Prentice Hall, Inc.

Example Write the molecular, ionic, and net ionic equations for the reaction that occurs when aqueous solutions of PbCl2 and Na2SO4 are mixed

Example Write the molecular, ionic, and net ionic equations for the reaction that occurs when Aqueous solution of Mg(NO3)2 and NH4OH are mixed