In terms of #pK_a#, which acid will be stronger? How does #pK_a# relate to #pK_b#?

2 Answers
anor277
Jul 5, 2017

#pH-=-log_10[H_3O^+]#, and thus bases, and then weaker acids will have the NUMERICALLY higher #pH#........

Explanation:

#"For example 1"#, the weaker acid will have the higher #pH#.

#"For example 2"#, the weaker acid will have the higher #pH#; the acid whose #K_a=8xx10^-6#.

#"For example 3"#, the stronger BASE will have the SMALLER #pK_b#, and thus the base with #pK_B=4.5# will give rise to the GREATER #[HO^-]# conc..........

We recall (i) that #pH=-log_10[H_3O^+]#,

and that #pOH=-log_10[HO^-]#.

And (ii) in aqueous solution under standard conditions, #pH+pOH=14#.......just as under these conditions #pK_a+pK_b=14#. The stronger the acid, the weaker the conjugate base, and vice versa.

David Drayer
Jul 5, 2017
  1. .1 M of a weak acid
    2 . Ka = #8 xx 10-6#
  2. pKb = # 4.5 #

Explanation:

Acid have a low pH the stronger the acid the lower the pH.
Bases have a high pH the strong the base the higher the pH.

  1. The .1 Molar solution of weak acid will have a higher pH than a strong acid.

  2. The Ka of # 10^-6# will be a weaker acid than one with a Ka of # 2xx 10^-3# so have a higher pH.

  3. The pkb of 4.5 is stronger than than a base with a pkb of 6.5.
    so the pkb of 4.5 will have a higher pH.

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