The Ka for dichloroacetic acid is 3.32 ×10^-2 . Approximately what percentage of the acid is dis

step 1 organic chemistry textbook. This problem deals with dichloroacetic acid. So we're given a K -A v

The Ka for dichloroacetic acid is 3.32 ×10^-2 ....

Key Concepts

Acid Dissociation Constant (Ka)

The acid dissociation constant, Ka, is a quantitative measure of the strength of an acid in solution. It represents the equilibrium constant for the dissociation reaction of the acid into its conjugate base and a proton. A larger Ka value indicates a stronger acid that dissociates more in water, while a smaller Ka signifies a weaker acid with less dissociation.

Chemical Equilibrium in Acid Dissociation

Acid dissociation is governed by chemical equilibrium, where the forward reaction (dissociation of the acid) and the reverse reaction (recombination of the ions) occur at equal rates. The equilibrium expression derived from this balance relates the concentrations of the hydrogen ion, the conjugate base, and the undissociated acid, forming the basis for using Ka to analyze the system.

Percentage Dissociation (Percent Ionization)

The percentage dissociation, also known as percent ionization, measures the fraction of the original acid that has dissociated into ions. It is calculated by taking the ratio of the concentration of the dissociated hydrogen ions to the initial concentration of the acid and converting this ratio into a percentage. This concept helps assess the extent to which an acid ionizes in solution.

Equilibrium Calculations and Approximations

When solving equilibrium problems involving acid dissociation, one often sets up an expression for Ka in terms of the unknown concentration of the ions produced. In many cases, approximations are made (such as assuming the change in concentration is small compared to the initial concentration) to simplify the calculations. However, it is important to check the validity of these approximations, especially when the acid strength leads to significant ionization.

Transcript

0:00 Organic chemistry textbook.

00:02 This problem deals with dichloroacetic acid.

00:08 So we're given a k -a value of 3 .32 times 10 to the negative 2.

00:13 And we're asked what percentage of the acid is dissociated in a 0 .10 molar aqueous solution.

00:21 Okay.

00:22 So to start, i just wrote those two pieces of data that we've been given on the left side of the screen.

00:30 And then i also wrote the equation that we'll be dealing with in this problem.

00:35 So we have dichlorocetic acid and water on the left side of the arrows.

00:41 And then on the right side, we have the dichloroacetate ion and the acid ion, h3oplus.

00:53 Okay, so the next thing that we're going to need to do is going to be to set up the k -a equation.

01:04 So we're going to have k -a equals concentration of products over concentration of reactants.

01:16 So we'll have cl2, ch, co2 minus.

01:24 And then we'll also have hydronium ion up top.

01:34 And then the bottom part of this equation is going to be our starting acid concentration.

01:42 So, cl2, c -h, c -o -2h.

01:48 Okay.

01:50 And remember, that is going to equal the k -a value that the problem gives us, which was 3 .32 times 10 to the negative 2.

02:01 Okay, so now that we've set that up, we need to use that to create an ice table.

02:10 And so we have the three species that we'll be dealing with in this problem.

02:15 So we have cl2, ch, c -o -2h.

02:24 We have the conjugate base, and then we have our hydronium ion.

02:43 Okay, so these are our three species, and we're making an ice table here.

02:48 So that is going to be the initial concentration, the change in concentration, and then the concentration at equilibrium.

03:00 Okay, so our initial concentration of the starting acid is going to be 0 .10 molar.

03:06 And again, we know that from the problem.

03:10 And the initial concentrations of our other two species are going to be zero because at the beginning there's none of them.

03:19 And so our equilibrium change is going to be minus y or you know any you can use any variable...

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