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 8.60×106.

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 4.50×103M ? The pKa of acetic acid is 4.76

the answer isnt 8.20

Explanation / Answer

XCH3COO is the salt of weak acid and strong base. so pH > 7

X+ concentration = 4.50 x 10^-3 M

CH3COO- concentration is also = 4.50 x 10^-3 M = C

pKa = 4.76

pH formula for strong base and weak acid

pH   = 7 + 1/2 [pKa + log C]

pH   = 7 + 1/2 [4.76 + log (4.50 x 10^-3)]

pH = 8.20

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