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

FREE Expert 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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Problem Details

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

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What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Weak Bases concept. If you need more Weak Bases practice, you can also practice Weak Bases practice problems.

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Based on our data, we think this problem is relevant for Professor Ramella's class at TEMPLE.