8. (5 points) Consider two aqueous solutions of nitrous acid (H NO2). Solution A

Question

8. (5 points) Consider two aqueous solutions of nitrous acid (H NO2). Solution A has a concentration of [H NO2] = 0.55 M, and Solution B has a concentration of [H NO2] = 1.25 M. Which statement about the two solutions is true? a. Solution A has the higher percent ionization and the higher pH. b. Solution B has the higher percent ionization and the higher pH. c. Solution A has the higher percent ionization, and Solution B has the higher pH. d. Solution B has the higher percent ionization, and Solution A has the higher pH.

Explanation / Answer

given HN02

the dissociation of HN02 is given as

HN02 ----> H+ + N02-

Ka = [H+] [N02-] / [HN02]

using ICE table

we get

[H+] = x

[N02-] = x

[HN02] = 0.55 - x

so

Ka = x * x / [C-x]

Ka = x2 / (C-x)

we know that the dissociation is very less

so

X<<<<< C

so

we get

Ka = x2/ C

x = sqrt ( ka * C)

now

pecent ionization = ([H+] / [HN02] ) * 100

percent ionization = ( x/C) * 100

percent ionization = sqrt( Ka * C) * 100 / C

percent ionization = 100* sqrt (Ka/C)

aslo

[H+] = x

so

pH = -log [H+]

pH = -log x

pH = -log sqrt(Ka *C)

pH = -log (Ka * C) ^1/2

pH = -0.5 log (Ka * C)

now

consider the two solutions

we got

percent ionization = 100* sqrt (Ka/C)

so from the above equation

higher the concentration lower the percent ionization

so

solution B has lower percent ionization

solution A has higher percent ionization

now

consider pH

pH = -0.5 log (Ka * C)

higher the concentration lower is the pH

so

soltuion B has lower pH and

solution A has higher pH

so

solution A has higher percent ionization and higher pH

so the answer is option A

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