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 8.40×106. 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 1.50×103 M ? The pKa of acetic acid is 4.76. Express your answer numerically.

Explanation / Answer

The Herbigon disscoiates to give cation and the ANion acetate

[X+] = 1.50×103 M

Ksp = [X+][CH3COO-] =8.40×106

[CH3COO-] = 8.40×106 / [X+] = 8.40×106 /1.50×103

                                               = 5.6 x 10-3 M = salt

its a buffer solution so the

pH = pka + log[Salt/Acid]

     = 4.76 + log(5.6 x 10-3/1)

     = 4.76 -2.25 =2.508

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