Ch.15 - Acid and Base EquilibriumWorksheetSee all chapters
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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

Solution: What is the pH of 0.688 M trimethylammonium iodide, (CH3)3NHI? Enter your answer with two decimal places. The Kb of trimethylamine, (CH3)3N, is 6.3 x 10-5.a. 3.68b. 0.16c. 9.79d. 4.98e. 7.00

Problem

What is the pH of 0.688 M trimethylammonium iodide, (CH3)3NHI? Enter your answer with two decimal places. 

The Kb of trimethylamine, (CH3)3N, is 6.3 x 10-5.

a. 3.68
b. 0.16
c. 9.79
d. 4.98
e. 7.00

Solution

We are being asked to calculate the pH of a 0.688 M trimethylammonium iodide, (CH3)3NHI.

(CH3)3NHI is a salt and it will break up in the solution:

(CH3)3NHI(aq) → (CH3)3NH+(aq) + I-(aq)

(CH3)3NH+ is the conjugate acid of a weak base ((CH3)3N):

       (CH3)3N    +   H2O(l)    →    (CH3)3NH+(aq)    +    OH-(aq)
     (weak base)                                 (conjugate acid)


Since we’re dealing with a weak acid, we will have to create an ICE chart to determine the equilibrium concentration of each species:

(CH3)3NH+ weak acid proton donor
H2O → will act as the weak base proton acceptor


Equilibrium reaction:        (CH3)3NH+(aq) + H2O(l)  (CH3)3N(aq) + H3O+(aq)

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