Reactions in Solution (Acids and Bases): Chapter 10. Chapter Outline. Chapter Outline

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1 Reactions in Solution (Acids and Bases): Chapter 10 Chapter utline Properties of Aqueous Solutions of Acids and Bases The Arrhenius Theory The ydronium Ion (ydrated ydrogen Ion) The BrØnsted-Lowry Theory The Autoionization of Water Amphoterism Strengths of Acids Chapter utline Acid-Base Reactions in Aqueous Solutions Acidic Salts and Basic Salts The Lewis Theory The Preparation of Acids 1

2 Strengths of Acids Ternary acid strength usually increases with: an increasing number of atoms on the central atom and an increasing oxidation state of central atom. Effectively, these are the same phenomenon. Every additional atom increases the oxidation state of the central atom by 2. Strengths of Acids or ternary acids having the same central atom: the highest oxidation state of the central atom is usually strongest acid. or example, look at the strength of the Cl ternary acids. Cl < Cl 2 < Cl 3 < Cl 4 weakest strongest Acid-Base Reactions in Aqueous Solution There are four acid-base reaction combinations that are possible: Strong acids strong bases Weak acids strong bases Strong acids weak bases Weak acids weak bases 2

3 Acid-Base Reactions in Aqueous Solution Strong acids - strong bases forming soluble salts This is one example of several possibilities hydrobromic acid calcium hydroxide The molecular equation is: 2 Br (aq) Ca() 2(aq) CaBr 2(aq) 2 2 () Acid-Base Reactions in Aqueous Solution Strong acids-strong bases forming insoluble salts There is only one reaction of this type: sulfuric acid barium hydroxide The molecular equation is: 2 S 4(aq) Ba() 2(aq) BaS 4(s) 2 2 () Acid-Base Reactions in Aqueous Solution Weak acids - strong bases forming soluble salts This is one example of many possibilities: nitrous acid sodium hydroxide The molecular equation is: N 2(aq) Na (aq) NaN 2(aq) 2 () 3

4 Acid-Base Reactions in Aqueous Solution Weak acids - weak bases forming soluble salts This is one example of many possibilities. acetic acid ammonia The molecular equation is: C 3 C (aq) N 3(aq) N 4 C 3 C (aq) The Lewis Theory Developed in 1923 by G.N. Lewis. This is the most general of the present day acid-base theories. Emphasis on what the electrons are doing as opposed to what the protons are doing. Acids are defined as electron pair acceptors. Bases are defined as electron pair donors. Neutralization reactions are accompanied by coordinate covalent bond formation. The Lewis Theory ne Lewis acid-base example is the ionization of ammonia. N N 4 base acid N N - 4

5 The Lewis Theory A second example is the ionization of Br. Br 2 3 Br - acid base _ Br Br Acid - it accepts the electron pair Base- it donates the electron pair covalent coordinate bond formed The Lewis Theory The reaction of sodium fluoride and boron trifluoride provides an example of a reaction that is only a Lewis acid-base reaction. It does not involve at all, thus it cannot be an Arrhenius nor a Brønsted-Lowry acid-base reaction. Na B 3 Na B - 4 You must draw the detailed picture of this reaction to determine which is the acid and which is the base. The Lewis Theory _ - B B Base - it donates the electron pair Acid - it accepts the electron pair coordinate covalent bond formed 5

6 The Preparation of Acids The binary acids are prepared by reacting the nonmetallic element with 2. 2(g) Cl 2(g) 2Cl (g) This reaction is performed in the presence of UV light. Volatile acids, ones with low boiling points, are prepared by reacting salts with a nonvolatile acid like sulfuric or phosphoric. NaCl (s) 2 S 4(conc.) NaS 4(s) Cl (g) Na (s) 2 S 4(conc.) NaS 4(s) (g) The Preparation of Acids We must use phosphoric acid to make Br and I. NaBr (s) 3 P 4(conc.) Na 2 P 4(s) Br (g) NaI (s) 3 P 4(conc.) Na 2 P 4(s) I (g) The Preparation of Acids Ternary acids are made by reacting nonmetal oxides (acid anhydrides) with water. S 2(g) 2 () 2 S 3(aq) N 2 5(g) 2 () 2 N 3(aq) Some nonmetal halides and oxyhalides react with water to give both a binary and a ternary acid. PCl 5(s) 4 2 () 3 P 4(aq) 5 Cl (aq) PCl 3() 3 2 () 3 P 4(aq) 3 Cl (aq) 6

7 Reactions in Aqueous Solution (Calculations): Chapter 11 Chapter utline Aqueous Acid-Base Reactions Calculations Involving Molarity Titrations The Mole Method and Molarity Equivalent Weights and Normality xidation-reduction Reactions The alf-reaction Method Adding in, -, or 2 to Balance xygen or ydrogen Stoichiometry of Redox Reactions Titrations Acid-base Titration Terminology Titration A method of determining the concentration of one solution by reacting it with a solution of known concentration. Primary standard A chemical compound which can be used to accurately determine the concentration of another solution. Examples include KP and sodium carbonate. 7

8 Titrations Acid-base Titration Terminology Standard solution A solution whose concentration has been determined using a primary standard. Standardization The process in which the concentration of a solution is determined by accurately measuring the volume of the solution required to react with a known amount of a primary standard. Titrations Acid-base Titration Terminology Indicator A substance that exists in different forms with different colors depending on the concentration of the in solution. Examples are phenolphthalein and bromothymol blue. Equivalence point The point at which stoichiometrically equivalent amounts of the acid and base have reacted. End point The point at which the indicator changes color and the titration is stopped. The Mole Method and Molarity Potassium hydrogen phthalate is a very good primary standard. It is often given the acronym, KP. KP has a molar mass of g/mol. C C C C C C C C K C C C C - K C C C C KP 2 aci di c 8

9 The Mole Method and Molarity Calculate the molarity of a Na solution if 27.3 ml of it reacts with g of KP. Na KP NaKP 2 Next Class: Reactions in Aqueous Solution (Calculations): Chapter 11 Start WL omework (Chapter 11) inish Reading Chapter 11 9