Lecture Presentation Chapter 11 Acids and Bases Karen C Timberlake General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter 11 Acids and Bases Clinical laboratory technicians prepare specimens for the detection of cancerous tumors and type blood samples for transfusions They must also interpret and analyze the test results, which are then passed on to the physician General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter 11 Readiness Key Math Skills • Solving Equations (1.4D) • Writing Numbers in Scientific Notation (1.4F) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter 11 Readiness Core Chemistry Skills • Writing Ionic Formulas (6.2) • Balancing a Chemical Equation (7.1) • Using Concentrations as a Conversion Factor (9.4) • Writing the Equilibrium Constant Expression (10.3) • Calculating Equilibrium Concentrations (10.4) • Using Le Châtelier’s Principle (10.5) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chapter 11 Acids and Bases A soft drink contains phosphoric acid (H3PO4) and carbonic acid (H2CO3) Learning Goal Describe and name acids and bases General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Arrhenius Acids Arrhenius acids • produce hydrogen ions (H+) when they dissolve in water HCl(g) • • • • H2O(l) H+(aq) + Cl−(aq) are also electrolytes, because they produce H+ in water have a sour taste turn blue litmus red corrode some metals General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Naming Acids • Acids with a hydrogen ion (H+) and a nonmetal (or CN−) ion are named with the prefix hydro and end with ic acid HCl(aq) hydrochloric acid • Acids with a hydrogen ion (H+) and a polyatomic ion are named by changing the end of the name of the polyatomic ion from ate to ic acid or ite to ous acid ClO3− chlorate ClO2− chlorite HClO3 chloric acid General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake HClO2 chlorous acid © 2016 Pearson Education, Inc Names of Common Acids General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Study Check Select the correct name for each of the following acids: HBr A bromic acid B bromous acid C hydrobromic acid H2CO3 A carbonic acid B hydrocarbonic acid C carbonous acid HBrO2 A bromic acid B hydrobromous acid C bromous acid General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Solution HBr Br−, bromide C hydrobromic acid The name of an acid with a hydrogen ion (H+) and a nonmetal uses the prefix hydro and ends with ic acid H2CO3 CO32−, carbonate A carbonic acid An acid with a hydrogen ion (H+) and a polyatomic ion ending in ate is called an ic acid HBrO2 BrO2−, bromite C bromous acid An acid with a hydrogen ion (H+) and a polyatomic ion ending in ite is called an ous acid General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Solution The Ka for acetic acid, HC2H3O2, is 1.8 × 10–5 What is the pH of a buffer prepared with 1.0 M HC2H3O2 and 1.0 M C2H3O2−? HC2H3O2(aq) + H2O(l) C2H3O2−(aq) + H3O+(aq) STEP State the given and needed quantities ANALYZE Given                 Need    THE  [HC2H3O2] = 1.0 M pH of solution PROBLEM [C2H3O2−] = 1.0 M Equation HC2H3O2(aq) + H2O(l)       C2H3O2−(aq) + H3O+(aq)  General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Solution The Ka for acetic acid, HC2H3O2, is 1.8 × 10–5 What is the pH of a buffer prepared with 1.0 M HC2H3O2 and 1.0 M C2H3O2−? HC2H3O2(aq) + H2O(l) C2H3O2−(aq) + H3O+(aq) STEP Write the Ka expression and rearrange for [H3O+] General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Solution The Ka for acetic acid, HC2H3O2, is 1.8  10–5 What is the pH of a buffer prepared with 1.0 M HC2H3O2 and 1.0 M C2H3O2−? HC2H3O2(aq) + H2O(l) C2H3O2−(aq) + H3O+(aq) STEP Substitute [HA] and [A−] into the Ka expression General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Solution The Ka for acetic acid, HC2H3O2, is 1.8  10–5 What is the pH of a buffer prepared with 1.0 M HC2H3O2 and 1.0 M C2H3O2−? HC2H3O2(aq) + H2O(l) C2H3O2−(aq) + H3O+(aq) STEP Use [H3O+] to calculate pH General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Calculating the pH of a Buffer Because Ka is a constant at a given temperature, • the [H3O+] is determined by the [HC2H3O2]/[C2H3O2−] ratio • the addition of small amounts of either acid or base changes the ratio of [HC2H3O2]/[C2H3O2−] only slightly • the changes in [H3O+] will be small and the pH will be maintained • the addition of a large amount of acid or base may exceed the buffering capacity of the system General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Buffers and pH Changes Buffers can be prepared from conjugate acid–base pairs such as H2PO4−/HPO42− and HPO42−/PO43−, HCO3−/CO32−, or NH4+/NH3 The pH of the buffer solution will depend on the conjugate acid–base pair chosen General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Buffers and pH Changes Using a common phosphate buffer for biological specimens, we can look at the effect of using different ratios of [H2PO4−/HPO42−] on the [H3O+] and pH The Ka of H2PO4− is 6.2 × 10−8 The equation and the [H3O+] are written as follows: H2PO4−(aq) + H2O(l) General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake H3O+(aq) + HPO42−(aq) © 2016 Pearson Education, Inc Buffers and pH Changes General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc Chemistry Link to Health: Buffers in Blood Plasma The arterial blood plasma has a normal pH of 7.35 to 7.45 If changes in H3O+ lower the pH below 6.8 or raise it above 8.0, cells cannot function properly and death may result In our cells, CO2 • is continually produced as an end product of cellular metabolism • is carried to the lungs for elimination, and the rest dissolves in body fluids such as plasma and saliva, forming carbonic acid, H2CO3 As a weak acid, carbonic acid dissociates to give bicarbonate, HCO3−, and H3O+ General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016  © 2016 Pearson Education, Inc Pearson Education, Inc Chemistry Link to Health: Buffers in Blood Plasma Kidneys also supply more of the bicarbonate anion, HCO3−, setting up an important buffer system in the body fluid: CO2(g) + H2O(l) H2CO3(aq) HCO3−(aq) + H3O+(aq) Excess H3O+ entering the body fluids reacts with the HCO3−, and excess OH− reacts with the carbonic acid H2CO3(aq) + H2O(l) HCO3−(aq) + H3O+(aq) Equilibrium shifts in the direction of the reactants General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016  © 2016 Pearson Education, Inc Pearson Education, Inc Chemistry Link to Health: Buffers in Blood Plasma Kidneys also supply more of the bicarbonate anion, HCO3−, setting up an important buffer system in the body fluid: CO2(g) + H2O(l) H2CO3(aq) HCO3−(aq) + H3O+(aq) • Excess H3O+ entering the body fluids reacts with the HCO3−: H2CO3(aq) + H2O(l) HCO3−(aq) + H3O+(aq) Equilibrium shifts in the direction of the reactants • Excess OH– entering the body fluids reacts with the H2CO3: H2CO3(aq) + OH−(aq) H2O(l) + HCO3−(aq) Equilibrium shifts in the direction of the products General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016  © 2016 Pearson Education, Inc Pearson Education, Inc Chemistry Link to Health: Buffers in Blood Plasma To maintain the normal blood plasma pH (7.35 to 7.45), • the ratio of [H2CO3]/[HCO3−] needs to be about to 10 • concentrations of 0.0024 M H2CO3 and 0.024 M HCO3− work to maintain that pH General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016  © 2016 Pearson Education, Inc Pearson Education, Inc Chemistry Link to Health: Buffers in Blood Plasma In the body, the concentration of carbonic acid is closely associated with the partial pressure of CO2, PCO2 • If the CO2 level rises, increasing H2CO3, the equilibrium shifts to produce more H3O+, which lowers the pH This condition is called acidosis • A lowering of the CO2 level leads to a high blood pH, a condition called alkalosis General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016  © 2016 Pearson Education, Inc Pearson Education, Inc Chemistry Link to Health: Buffers in Blood Plasma General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016  © 2016 Pearson Education, Inc Pearson Education, Inc Concept Map General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc ... sodium hydroxide General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake © 2016 Pearson Education, Inc General, Organic, and Biological Chemistry: Structures of Life,... acid General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake HClO2 chlorous acid © 2016 Pearson Education, Inc Names of Common Acids General, Organic, and Biological. .. drink contains phosphoric acid (H3PO4) and carbonic acid (H2CO3) Learning Goal Describe and name acids and bases General, Organic, and Biological Chemistry: Structures of Life, 5/e Karen C Timberlake