Ch.15 - Acid and Base EquilibriumWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
Problem

Given a weak acid HA and the following equilibrium in water:

HA(aq) ⇌ H+(aq) + A(aq)

which answer describes a situation where Kb for the conjugate base A will have the largest Kb value?

A. Ka = 7.0 × 10–8   and   T = 25 °C

B. Ka = 7.0 × 10–8   and   T = 80 °C

C. Ka = 9.0 × 10–6   and   T = 25 °C

D. Ka = 9.0 × 10–6   and   T = 80 °C

Solution

We are being asked to find determine which situation where Kb for the conjugate base A will have the largest Kb value.

    HA(aq)            H3O+(aq)  +    A-(aq)
     (weak acid)                                        (conjugate base)  


Hence, the Kb of A- can be calculated from the Ka of HA.  Ka and Kb are connected by the autoionization constant of water (Kw) in the following equation:

Kw=Ka·Kb

Kw = 1.0x10-14             @ 25°C

Kw=Ka·KbKwKa=Ka·KbKaKb=KwKa

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