As a chemist for an agricultural products company, you have just developed a new herbicide,"Herbigon," that you think has the potential to kill weeds effectively. A sparingly soluble salt, Herbigon is dissolved in 1 M acetic acid for technical reasons having to do with its production. You have determined that the solubility product Ksp of Herbigon is 9.5010^-6. Although the formula of this new chemical is a trade secret, it can be revealed that the formula for Herbigon is X-acetate (XCH_3COO, where "X" represents the top-secret cation of the salt). It is this cation that kills weeds. Since it is critical to have Herbigon dissolved (it won't kill weeds as a suspension), you are working on adjusting the pH so Herbigon will be soluble at the concentration needed to kill weeds. What pH must the solution have to yield a solution in which the concentration of X + is 5.0010^-3 M? The pKa of acetic acid is 4.76.

Question

Marin Mitchell

Chemistry

19 June, 21:58

As a chemist for an agricultural products company, you have just developed a new herbicide,"Herbigon," that you think has the potential to kill weeds effectively. A sparingly soluble salt, Herbigon is dissolved in 1 M acetic acid for technical reasons having to do with its production. You have determined that the solubility product Ksp of Herbigon is 9.5010^-6. Although the formula of this new chemical is a trade secret, it can be revealed that the formula for Herbigon is X-acetate (XCH_3COO, where "X" represents the top-secret cation of the salt). It is this cation that kills weeds. Since it is critical to have Herbigon dissolved (it won't kill weeds as a suspension), you are working on adjusting the pH so Herbigon will be soluble at the concentration needed to kill weeds. What pH must the solution have to yield a solution in which the concentration of X + is 5.0010^-3 M? The pKa of acetic acid is 4.76.

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Answers (1)

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Clinton Lam · Answer 1

PH to maximize the dissociation of acetic acid so as to push back the amount of acetate dissociating from the mystery compound.

Ksp = [X+][C2H3O2-] = 9.5*10^-6

Substituting in the desired value for [X+]

9.5*10^-6 = (5.0*10^-3) x

x, or acetate concentration, is. 0019

Now, we calculate the Ka of acetic acid:

pKa = - logKa

4.76 = - logKa

Ka = 1.738*10^-5

We want the concentration of acetate to be. 0019, so we plug that into our acid dissociation constant expression:

Ka = [H+][C2H3O2-]/[HC2H3O2]

1.738*10^-5 = [H+] (.0019) / 1

[H+] =.00915

pH = - log[H+]

pH = - log (.00915)

pH = 2.04