Base Solutions Write equations showing how each weak base...

Base Solutions Write equations showing how each weak base ionizes water to form $\mathrm{OH}^{-}$ . Also write the corresponding expression for $K_{\mathrm{b}} .$ $$\begin{array}{l}{\text { a. } \mathrm{NH}_{3}} \\ {\text { b. } \mathrm{HCO}_{3}^{-}} \\ {\text { c. } \mathrm{CH}_{3} \mathrm{NH}_{2}}\end{array}$$

Base Solutions
Write equations showing how each weak base ionizes water to form
$\mathrm{OH}^{-}$ . Also write the corresponding expression for $K_{\mathrm{b}} .$
$$\begin{array}{l}{\text { a. } \mathrm{NH}_{3}} \\ {\text { b. } \mathrm{HCO}_{3}^{-}} \\ {\text { c. } \mathrm{CH}_{3} \mathrm{NH}_{2}}\end{array}$$

Key Concepts

Weak Base Ionization Reaction

In aqueous solutions, weak bases react with water by accepting a proton from H2O, producing their conjugate acid and hydroxide ions. This partial ionization is represented by a reversible reaction where water acts as a proton donor, and the reaction does not go to completion. The process is central to understanding the behavior of weak bases in solution as it explains how they generate OH? ions and affect the pH of the solution.

Base Ionization Constant (Kb)

The base ionization constant, Kb, quantifies the extent of ionization of a weak base in water. It is defined as the ratio of the product of the concentrations of the formed hydroxide ion and the conjugate acid to the concentration of the un-ionized base at equilibrium. This equilibrium expression is crucial for comparing the strengths of different weak bases, and a higher Kb indicates a stronger base that ionizes to a greater extent.

Equilibrium in Acid-Base Reactions

Acid-base reactions in aqueous solutions generally do not proceed to completion but instead establish an equilibrium. Understanding the concept of chemical equilibrium helps to explain how the concentrations of reactants and products remain constant over time in the ionization reactions of weak bases. This equilibrium approach allows for the application of equilibrium constants such as Kb to predict the behavior of bases in various chemical contexts.

Transcript

00:01 So here we have three different bases, and so our first one is nh3.

00:05 Now, remember, the definition of a base is that it's a proton or an h plus.

00:13 That's the same thing, proton acceptor.

00:19 And so when nh3 reacts with water, so because we just believe the word is saying, we basically we put this ammonia base in the water, what's going to happen is if it's a proton acceptor, it's going to gain, so plus a proton h plus.

00:35 And well, it has to come from somewhere.

00:37 The only other thing is the water.

00:38 So the water has to lose the h plus.

00:43 We have minus h plus.

00:44 And so you can see this proton is being transferred over here.

00:49 So our products then are going to be, well, our nh3 is going to go from having just three hydrogens to four, three plus this one right here, and h4 and then a positive charge.

01:01 And then over here we're going to have o, still one oxygen, but only one hydrogen here.

01:07 So, oh, h minus.

01:10 Technically you could say h0 minus, but no one says that.

01:12 So right, it is oh minus.

01:14 And so this is how this weak base, nh3, produces oh minus in water.

01:20 Now, our kb, our equilibrium constant for this reaction, is going to be first the concentration of nh4 plus times the concentration of oh minus over the concentration of nh3.

01:35 Of course, we ignore water here because it's a liquid, and so liquids aren't part of the mass action pressure.

01:43 So this is what we have here.

01:44 Our next one is h.

01:48 Co3 minus.

01:49 And so when it reacts with water, it's the same thing is going to happen...

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