Which of the following solutions at equimolar solution would give the LOWEST #pH#?

#(a)# #"acetonitrile;"#
#(b)# #"calcium hydroxide;"#
#(c)# #"potasium hydroxide;"#
#(d)# #"hydroiodic acid;"#
#(e)# #"ammonia."#

1 Answer
Nov 1, 2016

Answer:

#Ca(OH)_2; KOH; NH_3; HC-=N; HI#

Explanation:

Hydrogen iodide is definitely the strongest acid in aqueous solution, and thus will give the lowest #pH#.

Hydrocyanic acid is a fairly weak Bronsted acid, but still the #pH# will be well below #7#:

#H-C-=N + H_2O rightleftharpoons H_3O^+ + N-=C^-#

Next cab off the rank is ammonia, which is a weak base in aqueous solution:

#NH_3(aq) + H_2O rightleftharpoons NH_4^+ + HO^-#

#KOH# and #Ca(OH)_2# are strong Bronsted bases, and will dissolve to give quantitative hydroxide ion. Since, you specified equal concentrations, calcium hydroxide delivers 2 equiv hydroxide anion, and will thus give the most basic solution, with the highest value of #pH#.