Practice Exercise 16.34 To study the effects of a weakly acidic medium on the ra

Question

Practice Exercise 16.34 To study the effects of a weakly acidic medium on the rate of corrosion of a metal alloy, a student prepared a buffer solution containing both 0.125 M NaC2H302 and 0.082 M HC2H302. Calculate the pH of the buffer using the K, for C2Hy02. Be sure to write the chemical equation for the equilibrium as the reaction of CpHjO2 with water. Then use the chemical equation as a guide in setting up the equilibrium expression for Kb For acetic acid, HC2Hy02, K -1.8 x 10. pH= The number of significant digits is set to 3; the tolerance is +-1 in the 3rd significant digit

Explanation / Answer

Solution:- The equation for the reaction of acetate ion with water would be...

CH3COO-(aq) + H2O(l) <------> CH3COOH(aq) + OH-

We would make the ice table and solve it.

  CH3COO-(aq) + H2O(l) <------> CH3COOH(aq) + OH-

I 0.125 0.082 0

E -X +X +X

C 0.125 - X 0.082 + X X

Kb = [(0.082 + X)(X)]/(0.125 - X)

Kb = Kw/Ka = 1.0 x 10-14/1.8 x 10-5 = 5.6 x 10-10

5.6 x 10-10 =  [(0.082 + X)(X)]/(0.125 - X)

5.6 x 10-10(0.125 - X) = (0.082 + X)(X)

since the Kb value is too low so the approxymation could be used and so 0.082 +X and 0.125 - X could be taken as 0.082 and 0.125.

5.6 x 10-10(0.125) = (0.082)(X)

X = 5.6 x 10-10 x 0.125/0.082 = 8.54 x 10-10

[OH-] = 8.54 x 10-10

pOH = - log 8.54 x 10-10

pOH = 9.07

pH = 14 - 9.07

pH = 4.93

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.