# Question Video: Identifying the Factor That Increases the Degree of Dissociation of a Weak Acid in a Set of Factors Chemistry

Which of the following factors would increase the degree of dissociation of a weak acid? [A] Increasing dilution [B] Decreasing volume [C] Decreasing dilution [D] Increasing acid concentration

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### Video Transcript

Which of the following factors would increase the degree of dissociation of a weak acid? (A) Increasing dilution, (B) decreasing volume, (C) decreasing dilution, (D) increasing acid concentration.

When a weak acid is mixed with water, only a portion of the molecules dissociate into ions. We can represent the extent to which the molecules dissociate with the degree of dissociation. Degree of dissociation, typically given the symbol 𝛼, is the proportion of the substance that is dissociated. The degree of dissociation is dependent on a number of factors, including the strength of the acid, temperature, and concentration. The strength of an acid can be quantified using an acid dissociation constant, or 𝐾 a. The degree of dissociation, 𝐾 𝐚, and the initial concentration of the acid, represented by 𝑐 naught, can be related to one another using Oswald’s dilution law.

For weak acids with very low degrees of dissociation, one minus 𝛼 can be approximated to one. And Oswald’s dilution law can be simplified to 𝐾 𝐚 is approximately equal to 𝛼 squared times 𝑐 naught. This can be rearranged to solve for the degree of dissociation. Here, we can see that the degree of dissociation is inversely proportional to the square root of the acid concentration. Thus, increasing the concentration will decrease the degree of dissociation, and decreasing the concentration will increase the degree of dissociation. We want to determine which factor would cause the degree of dissociation to increase. So we need to determine which factor would cause the concentration to decrease.

Answer choice (A), increasing dilution means that we are adding more solvent to the solution. Increasing the amount of solvent will cause the concentration to decrease. A decrease in concentration corresponds with an increase in the degree of dissociation. Let’s look at answer choice (B). Decreasing the volume of the solvent will increase the concentration, so the degree of dissociation will decrease. Answer choice (C) is the opposite of answer choice (A). Decreasing dilution will cause an increase in the concentration, so the degree of dissociation will decrease. Lastly, we know that increasing the acid concentration will cause a decrease in the degree of dissociation. So the factor that would increase the degree of dissociation of a weak acid is answer choice (A), increasing dilution.