CHEM 230 Exam 2 Questions With Complete Solutions

What is the principal form of benzoic acid at pH 8.2 if the pKa value is 4.2 correct answer: So, at pH 4.20, there is a 1:1 mixture of benzoic acid (HA) and benzoate ion (A-). At pH = pKa + 1 (= 5.20), the quotient [A-]/[HA] is 10:1. At pKa + 2 (= 6.20), the quotient [A-]/[HA] is 100:1. As pH increases, all the way to pKa + 4 the [A-]/[HA] is 10000:1 *The predominant form of benzoic acid at pH 8 is the benzoate anion For a monoprotic system, the species ___ is the predominant form when pH > pKa. correct answer: the basic species A- is the predominant form when pH > pKa. The species ___ is the predominant form when pH < pKa. correct answer: HA is the predominant form when pH < pKa. A- is basic/acidic? HA is basic/acidic? correct answer: A- is basic HA is acidic Speciation describes describes what? correct answer: the distribution of analyte among possible species. For an acid or base, speciation describes how much of each protonated form is present. Activity correct answer: Accounts for the ionic strength in a chemical reaction Activity coefficient measures the deviation from 1 As the ionic strength increases the coefficient goes towards ____ As the ionic strength decreases the coefficient goes towards ____ correct answer: As the ionic strength increases, the activity coefficient decreases towards 0 As the ionic strength decreases, the activity coefficient increases towards 1 As the magnitude of charge of an ion increases, the activity coefficient ____ correct answer: decreases Fractional Composition correct answer: The portion of a given ion in a solution Redox Reaction correct answer: When electrons from a redox reaction flow through an electric circuit, current and voltage can be measured In a redox reaction Current is proportional to ___