I cannot figure out this problem. Please explain in detail with answer. Question

Question

I cannot figure out this problem. Please explain in detail with answer. Question 10 Suppose you wanted to produce an aqueous solution of pH 8.60 by dissolving one of the following salts in water: NH4Cl, KHSO4, KNO2, NaNO3 Part A Which salt would you use? NH Cl KHSO O KNO2 NaNO, My Answers Give Up Submit Correct Part B At what molarity? Express your answer using two significant figures. molarity 4410 M My Answers Give Up Submit All attempts used; correct answer withheld by instructor Continue Provide Feedback

Explanation / Answer

Part A)

To prepare a solution of pH 8.60, we would use a salt whose pKa is closest to the required pH

So the salt to be used is,

NH4Cl

pKa of NH4+ = 9.25

Part B)

pH = -log[H3O+] = 8.60

molarity of [H3O+] needed = 2.51 x 10^-9 M

     NH4+ + H2O <==> NH3    + H3O+

Ka = [NH3[H3O+]/[NH4+]

[NH3] = [H3O+]

So,

5.55 x 10^-10 = (2.51 x 10^-9)^2/(x + 2.51 x 10^-9)

x = 8.84 x 10^-9 M

Molarity of NH4Cl needed = 8.84 x 10^-9 M

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