Identify the strongest acid and the strongest conjugate base. Select one or more

Question

Identify the strongest acid and the strongest conjugate base. Select one or more: a. HCN b. CN^- c. CH_3CO_2H d. CH_3CO_2^- e. HNO_2 f. NO_2^- A water sample taken from a bore has a hydroxide ion concentration, [OH^-], of 7.34 times 10^-8 M, at 25 degree C. What is the pH of the solution? Answer: Dissolving ammonium chloride (NH_4Cl) in water gives a non-neutral solution. Write a balanced chemical equation showing which ion or ions are responsible for this effect. Is the resulting solution acidic or basic?

Explanation / Answer

1) less pKa = strong acid

   Hence, HNO2 is the strongest acid.

---------------------------------

    More pka = weak acid     

   Weak acids have strong conjugate bases.

Since HCN has more pKa, HCN is a weak acid and CN- is the strongest conjugate base.

Therefore,

ans = b,e

2)

    Given that [OH-] = 7.34 x 10-8 M

      pOH = -log [OH-] = - log [ 7.34 x 10-8] = 7.13

   Then,

   pH = 14-pOH = 14-7.13 = 6.87

Therefore,

pH = 6.87

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