Lecture 18 PDF

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This is Dr. Dillon's lecture on weak acids and bases as well as polyprotic acids. The majority of her lecture were problems, but some were content and vocab. Hope it helps!...

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Lecture 18.1 Dillon CHM1046 Weak Acids and Bases that exist in equilibrium Weak Acids and bases only partially dissociates unlike strong ones which dissociate fully and does not exist in equilibrium Ka and Kb Values  Ka is the equilibrium constant for bases and the Kb value is for the bases  Ionization constants are the measure of the strengths of acids and bases. The larger the Ka or Kb, the stronger the acid or bas, respectively. K  The only thing that can change to the constant is temperature.  The rules for equilibrium constants apply to the dissociation of acids and bases Weak acids only ionize to a small extent and come to a state of equilibrium. You can calculate the equilibrium [] the same way as the other equilibrium problems. Problem solving approach 1. Write a balanced equation (ALWAYS THE FIRST THING) 2. Write an expression for Ka 3. Define x as the change in concentration that occurs during the reaction 4. Construct a reaction table in terms of x 5. Male assumptions that simplify the calculations 6. Sub. Values into the Ka expression and solve for x 7. Check that the assumptions are justified

Lecture 18.2 Polyprotic Acids – acids that accept/donate multiple protons. An acid with one ionizable proton. This goes through dissociation through a step wise process.  Ka1 > Ka2> Ka3. Because Ka1 is larger, it means that it contributes to the donation of protons to the solution the most. The rest following are VERY weak acids. In Ka2 and Ka3 it can sometimes be negligible. What is the pKa? It is the negative log of the Ka. This is a way for us to work with the numbers that are really small to identify if an acid or base is weak or strong. The LOWER the pKa value the stronger the acid....