How to predict whether the aqueous solution for the following salts are acidic , basic or neutral (a)NH4Br (b)KClO4 (c)NaHC2O4 (d)CsBr (e)KHSO4 (f)[CH3NH3]Cl?

1 Answer
Jan 17, 2016


#a. acid; b. "neutral"; c. acid; d. "neutral"; e. acid; f. acid#


You have weak acids, ammonium bromide, sodium oxalate, potassium bisulfate, and ammonium bromide. And neutral salts: potassium perchlorate, and caesium bromide. The only potential problem is sodium oxalate.

The parent acid, oxalic acid, has #pK_(a1) =1.25# and #pK_(a2) =4.14#. Of course, #pK_(a2)# is the one that concerns us. Compare #pK_(a2)# to #pK_a# ammonium bromide, #4.76# (that's from memory, I could not find my old notes, so check on me!). So sodium oxalate is a stronger acid than ammonium bromide, and will thus give also a slightly acidic solution in water.

Another way to look at this is by the strong acid/weak base formalism. Since we are chemists, physical scientists (hopefully!), I would always prefer to get the numbers, and find the #pK_a's#.