Chapter 14 Acids and Bases 14.3 Strengths of Acids and Bases Learning Goal Write equations for the dissociation of strong and weak acids; identify the direction of reaction. Acids produce hydrogen ions in aqueous solution. © 2014 Pearson Education, Inc.

Strength of Acids and Bases The strength of an acid is determined by the moles of H3O+ produced per mole of acid that dissociates. The strength of a base is determined by the moles of OH− produced per mole of base that dissolves. © 2014 Pearson Education, Inc.

Strong and Weak Acids A solution of hydrochloric acid forms as H+ transfers from hydrogen chloride to water. Water is acting as a base in this reaction. © 2014 Pearson Education, Inc.

Strong acids are strong electrolytes. They donate H+ easily ionize completely in water HCl(g) + H2O(l)  H3O+(aq) + Cl−(aq) There are six strong acids: Strong acid Hydroiodic acid HI Hydrochloric acid HCl Hydrobromic acid HBr Sulfuric acid H2SO4 Perchloric acid HClO4 Nitric acid HNO3 © 2014 Pearson Education, Inc.

Strong versus Weak Acids A strong acid such as HCl completely dissociates 100%. Weak acids such as HC2H3O2 are only slightly ionized in water to form a solution. © 2014 Pearson Education, Inc.

Strong versus Weak Acids A weak acid, HC2H3O2 , slightly dissociates: HC2H3O2(aq) + H2O(l) H3O+(aq) + C2H3O2−(aq) A strong acid, HCl, dissociates 100%: HCl (aq) + H2O(l)  H3O+(aq) + Cl−(aq) Notice the different reaction arrows used. © 2014 Pearson Education, Inc.

Weak acids are weak electrolytes. They transfer only a small percentage of H+ ions only partially ionize in water have a strong conjugate base have a forward and reverse reaction have a strong reverse reaction HC2H3O2(aq) + H2O(l) H3O+(aq) + C2H3O2−(aq) Acetic acid Acetate ion © 2014 Pearson Education, Inc.

There are many weak acids: citric acid, found in oranges and other citrus fruits acetic acid, found in vinegar, used in salad dressings phosphoric acid, found in many soft drinks © 2014 Pearson Education, Inc.

Relative Strength of Acids © 2014 Pearson Education, Inc.

donate one H+ ion at a time Diprotic Acids Diprotic acids can donate two H+ ions donate one H+ ion at a time © 2014 Pearson Education, Inc.

Diprotic Acids Sulfuric acid, H2SO4 , a strong acid, ionizes 100% to form HSO4− and H+. Bisulfate, HSO4−, is considered a weak acid; it only partially ionizes to form SO42−. © 2014 Pearson Education, Inc.

Strong versus Weak Acids Strong acids produce a higher concentration of H+ ions in solution than weak acids. © 2014 Pearson Education, Inc.

Strong versus Weak Bases Bases are found in many household products, such as those that remove grease and open drains. © 2014 Pearson Education, Inc.

are strong electrolytes Strong Bases Strong bases are strong electrolytes dissociate completely in water to give metal ions and hydroxide ions KOH(s)  K+(aq) + OH−(aq) H2O © 2014 Pearson Education, Inc.

Strong Bases Strong bases include Group 1A (I) hydroxides and some Group 2A (II) hydroxides. Strong Bases Lithium hydroxide LiOH Sodium hydroxide NaOH Potassium hydroxide KOH Strontium hydroxide Sr(OH)2 Calcium hydroxide Ca(OH)2 Barium hydroxide Ba(OH)2 © 2014 Pearson Education, Inc.

Strong Bases High concentrations of hydroxide ions in household products can cause severe damage to skin and eyes. It is important to follow directions carefully when hydroxide ions are used in the home or a chemistry laboratory. © 2014 Pearson Education, Inc.

Weak bases produce very few ions in solution and are poor electrolytes poor acceptors of hydrogen ions A typical weak base ammonia, NH3, used in window cleaners, reacts with water to form NH4+ and OH−. NH3(g) + H2O(l) NH4+(aq) + OH−(aq) © 2014 Pearson Education, Inc.

In acid−base reactions, one acid is stronger than the other acid Direction of Reaction In acid−base reactions, one acid is stronger than the other acid one base is stronger than the other base In a conjugate acid−base pair, the stronger the acid, the weaker its conjugate base the stronger the base, the weaker its conjugate acid © 2014 Pearson Education, Inc.

Direction of Reaction Comparing the strengths of acids and bases in a chemical reaction, we can determine the direction of the reaction. © 2014 Pearson Education, Inc.

Identify each of the following as a strong or weak acid or base: HBr Learning Check Identify each of the following as a strong or weak acid or base: HBr HNO2 NaOH H2SO4 E. Cu(OH)2 © 2014 Pearson Education, Inc.

Identify each of the following as a strong or weak acid or base: Solution Identify each of the following as a strong or weak acid or base: HBr strong acid HNO2 weak acid NaOH strong acid H2SO4 strong acid E. Cu(OH)2 weak base © 2014 Pearson Education, Inc.

A. Identify the stronger acid in each pair. 1. HNO2 or H2S Learning Check A. Identify the stronger acid in each pair. 1. HNO2 or H2S 2. HCO3− or HBr B. Identify the stronger base in each pair. 1. CO32− or NO2− 2. OH− or H2O © 2014 Pearson Education, Inc.

A. Identify the stronger acid in each pair. 1. HNO2 or H2S HNO2 Solution A. Identify the stronger acid in each pair. 1. HNO2 or H2S HNO2 2. HCO3− or HBr HCO3− B. Identify the stronger base in each pair. 1. CO32− or NO2− CO32− 2. OH− or H2O OH− © 2014 Pearson Education, Inc.