Textbook 6D.13

[Miguel Hernandez LEC 3]

Rank the following solutions in order of increasing pH:
(a) 1.0 3 1025 m HCl(aq); (b) 0.20 m CH3NH3Cl(aq); (c) 0.20 m
CH3COOH(aq); (d) 0.20 m C6H5NH2(aq). Justify your ranking

I was wondering if there was a method to solve this problem without directly calculating the pH of each of these with ICE tables. Thanks!

[Nathan_Su_Dis3F]

I don't think so, since it isn't just a list of oxyacids; you need to calculate pH.

[Nadia Nichol]

I am pretty sure that you are able to solve without solving, it is just a lot of remembering concepts from 14a. First, the solutions are ranked by the relative strengths. Strong acids like HCl result in the lowest pH, and then it is salts that are made with a combination of weak bases and strong acids and then lastly it would be anything that could be considered a weak base because they have higher pHs, actual calculations are handy if you do not remember these things or if one or more weak bases or etc is included.

[Emerson Gaspar 1D]

At first glance, you can determine that HCl is a strong acid, CH3NH3CL is a salt, CH3COOH is a weak acid, and C6H5NH2 is a weak base. For HCl, we could just do pH = -log(1.0x10^-5) = 5. For CH3NH3CL andC6H5NH2 we would have to use the Ka = Kw/Kb and get the pH from [H+]. For CH3COOH, we could just do Ka = 1.8 x 10-5.