As a chemist for an agricultural products company, you have just developed a new

Question

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 8.30×106.

Although the formula of this new chemical is a trade secret, it can be revealed that the formula for Herbigon is X-acetate (XCH3COO, 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 6.00×103M ? The pKa of acetic acid is 4.76.

Explanation / Answer

we need X+ = 6x10^-3 M = 0.006 M

XCH3COO (s) <---> X+ (aq) + CH3COO- (aq)

Ksp = [X-][CH3COO-]

8.3 x 10^ -6 = 0.006 x [CH3COO-]

[CH3COO-]   = 0.0013833

pH = pka + log [CH3COO-]/[CH3COOH]

pH = 4.76 + log ( 0.0013833) /1

pH = 1.9

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