Question

For each of the following scenarios, determine the missing Ho'l.ph, puno nja on the information given. If the missing pieces of information cannot be determined for a given thal, write, cannot be determined and explain why. Hint: The answer is the unknown cannot be determined for only one of the solutions below. Show all work (4 points each) a. The concentration of a NH, solution is 0.1 M. Find [H,O'). (OH), pH, and POH [H,0")= (OH)= pH POH b. pH = 4.8; Find: pOH, [H,0") and (OH) рона [H,O'= (OH)- c. (OH)- 8.2 x 10' M; Find: pH, POH, and [H,0") POH= [H,0")= d. The concentration of HNO in a solution is 2.0 M. Find (H,0"), (OH), pH, and POH [H,0"]= (OH)=_ pH= POH=-

Answer 1

a.

NH₃ is weak base, pKb = 4.75

C = 0.1

Hence,

pOH = $\frac{1}{2}$ (pKb - logC)

Or, pOH = $\frac{1}{2}$ ( 4.75 - log 0.1)

= $\frac{1}{2}$ ( 4.75 + 1)

= 2.875.

[OH^-] = 10^-pOH = 10^-(2.875) = 0.00133 M

pH = 14 - pOH = 14 - 2.875 = 11.125.

[H₃O⁺] = 10^-pH = 10^-11.125 = 7.5×10^-12 M.

b.

pH = 4.8, [H₃O⁺] = 10^-4.8 = 1.58 ×10^-5 M

pOH = 14 - 4.8 = 9.2 , [OH^-] = 10^-9.2 = 6.31 ×10^-10 M.

c.

[OH^-] = 8.2×10^-9 M

pOH = - log (8.2×10^-9) = 8.09

pH = 14 - 8.09 = 5.91

[H⁺] = 10^(-5.91) = 1.2 ×10^-6 M.

d.

HNO₃ is strong acid , hence Concentration of HNO₃ = [H₃O⁺] = 2.0 M

pH = - log [H₃O⁺] = - log (2.0) = 0.3

pOH = 14 - 0.3 = 13.7

[OH^-] = 10^-13.7 = 1.995 × 10^-14 M.