Calculate the pH of a solution of 0.0030 M potassium arsenite, KH 2 AsO 3 . The

Question

Calculate the pH of a solution of 0.0030 M potassium arsenite, KH2AsO3. The conjugate weak acid of the arsenite ion, H3AsO3 has Ka   =   5.1 x 1010. (It only has one acidic H in water.)

Citric acid is a triprotic weak acid with pKa's = 3.13, 4.76 and 6.40. Let H3Cit represent the fully protonated form, and circle the conjugate acid/base pair below that should be chosen for a buffer at pH = 4.65.  

Circle one:  

          H3Cit / Cit3             H2Cit / HCit2          HCit2 / Cit3               H3Cit/ HCit2                 H3Cit / H2Cit   

(b) (0.5 pts) Calculate ratio of conjugate base-to-conjugate acid to prepare the pH 4.65 buffer in part (a).   

Explanation / Answer

Calculate the pH of a solution of 0.0030 M potassium arsenite, KH 2 AsO 3 . The

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