Calculate K a of proprionic acid (CH 3 CH 2 CO 2 H) if [CH 3 CH 2 CO 2 H] eq = 0.2 M & [CH 3 CH 2 CO 2 - ] eq = 1.62 x 10 -3 M.

So this practice problem wants us to calculate the Ka, the acid dissociation constant of propionic acid shown here, if the concentration of propionic acid at equilibrium is equal to 0.2 molar and the conjugate base of propionic acid at equilibrium concentration is equal to 1.62 times 10 to the negative 3rd molar. And so recall that the Ka is simply the, equilibrium constant for the acid dissociation. So h a here is the acid, which would be propionic acid, and H+ would be the ion, the hydrogen ion, and A minus is the conjugate base here. And so, the acid dissociation constant is gonna be the concentration of products over the concentration of reactants. So the products are H+ and A minus, and the reactant is And so if we rewrite this using the bottom formula here with propionic acid, this is what we get. And so at equilibrium, we know the concentration of propionic And so And so in order to do that, what we can do is apply our ICE table, which I know you guys remember from your previous chemistry courses. So here's a little refresher. ICE is initial, change, equilibrium. And so, we're given that we have this propionic acid solution here, and so at equilibrium, we know that the concentration is 0.2 molar and the concentration of the, conjugate base is 1.62 times 10 to the negative 3rd molar. And so if we assume the initial concentrations of each of these guys on the reactive side is 0, then, here we have some initial, x of propionic acid, which we're not really given and we don't really care about it too much. But what we do know is that there's got to be a change in the concentration here. And so the change has to match, the change that we see here. So there has to be plus 1.62 times 10 to the negative 3rd molar. And then the same change has to apply here. And so, what that means is that we're gonna have to have a concentration of 1.62 times 10 to the negative 3rd molar hydrogen ion. And so here we would have a deduction of negative 1.62 times 10 to the negative 3rd. And so all we're really interested in is this value here to plug it in up into this equation. And so what we realize is that really what we can do is take 1.62 times 10 to the negative 3rd and square that value. So what we end up getting is k a is equal to 1 0.62 times 10 to the negative 3rd molar, squared, since we have the same value multiplied by itself, over 0.2 molar. And so when we, type this all into our calculator, what we end up getting is 1.312 times 10 to the negative 5th, which is about equal to 1 point 3 times 10 to the negative 5th. And so that's our k a. Our k a is 1.3 times 10 to the negative 5th. And notice that matches answer option a here. So the other answers are incorrect and we can indicate that a here is the correct answer. And I'll see you guys in our next video.

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2. Water

Acid Dissociation Constant

Biochemistry

2. Water

Acid Dissociation Constant

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Multiple Choice

Calculate K_a of proprionic acid (CH ₃CH₂CO₂H) if [CH₃CH₂CO₂H]_eq= 0.2 M & [CH₃CH₂CO₂^-]_eq= 1.62 x 10^-3 M.

K_a = 1.3 x 10^-5

K_a = 7.8 x 10^-10

K_a = 3.9 x 10^-12

K_a = 5.1 x 10^-4

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Verified step by step guidance

Understand that the acid dissociation constant (Ka) is a measure of the strength of an acid in solution. It is defined by the equilibrium concentrations of the acid and its dissociated ions.

Write the chemical equation for the dissociation of propionic acid: CH3CH2CO2H ⇌ CH3CH2CO2- + H+.

Use the expression for Ka: Ka = [CH3CH2CO2-][H+]/[CH3CH2CO2H]. Note that [H+] is equal to [CH3CH2CO2-] at equilibrium for a weak acid.

Substitute the given equilibrium concentrations into the Ka expression: Ka = (1.62 x 10^-3 M)(1.62 x 10^-3 M)/(0.2 M).

Calculate the value of Ka using the substituted values, ensuring to maintain the correct units and significant figures throughout the calculation.

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Struggling with Biochemistry?

Calculate Ka of proprionic acid (CH 3CH2CO2H) if [CH3CH2CO2H]eq = 0.2 M & [CH3CH2CO2-]eq = 1.62 x 10-3 M.

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Acid Dissociation Constant practice set

Calculate K_a of proprionic acid (CH ₃CH₂CO₂H) if [CH₃CH₂CO₂H]_eq= 0.2 M & [CH₃CH₂CO₂^-]_eq= 1.62 x 10^-3 M.