Unit 4 Objectives
By the end of this unit, you will be able to:
- Calculate pH of a polyprotic acid solution
- Describe the acid/base properties of ions and salts
- Describe buffers and how they work using the common ion effect and Le Chatelier's Principle
- Use Henderson Hasselbalch equation to build buffer systems
- Calculate pH of buffers (initially and after added acid or base)
- Describe the process of acid/base titration and identify specific points of a titration curve
- Mathematically describe SA/SB, WA/SB and SA/WB titration
- Use different techniques to monitor acid/base titrations
- 4.1: Polyprotic Acids
- An acid that contains more than one ionizable proton is a polyprotic acid. The protons of these acids ionize in steps. The differences in the acid ionization constants for the successive ionizations of the protons in a polyprotic acid usually vary by roughly five orders of magnitude. As long as the difference between the successive values of Ka of the acid is greater than about a factor of 20, it is appropriate to break down the calculations of the concentrations sequentially.
- 4.2: The Acid-Base Properties of Ions and Salts
- A salt can dissolve in water to produce a neutral, a basic, or an acidic solution, depending on whether it contains the conjugate base of a weak acid as the anion ( A−A− ), the conjugate acid of a weak base as the cation ( BH+ ), or both. Salts that contain small, highly charged metal ions produce acidic solutions in water. The reaction of a salt with water to produce an acidic or a basic solution is called a hydrolysis reaction.
- 4.3: Acid rain
- The damaging effects of acid rain have led to strong pressure on industry to minimize the release of harmful reactants. Acid rain is rainfall whose pH is less than 5.6, the value typically observed, due to the presence of dissolved carbon dioxide. Acid rain is caused by nitrogen oxides and sulfur dioxide produced by both natural processes and the combustion of fossil fuels. Eventually, these oxides react with oxygen and water to give nitric acid and sulfuric acid.
- 4.4: Buffers- Solutions That Resist pH Change
- Buffers are solutions that resist a change in pH after adding an acid or a base. Buffers contain a weak acid ( HA ) and its conjugate weak base (A−). Adding a strong electrolyte that contains one ion in common with a reaction system that is at equilibrium shifts the equilibrium in such a way as to reduce the concentration of the common ion. Buffers are characterized by their pH range and buffer capacity.
- 4.5: Titrations and pH Curves
- The shape of a titration curve, a plot of pH versus the amount of acid or base added, provides important information about what is occurring in solution during a titration. The shapes of titration curves for weak acids and bases depend dramatically on the identity of the compound. The equivalence point of an acid–base titration is the point at which exactly enough acid or base has been added to react completely with the other component.