Textbook 6D.13

[Sophia Schiro]

Can someone walk through how they did this textbook problem?
Rank the following solutions in order of increasing pH: (a) 1.0 x 10^-5 M HCl(aq); (b) 0.20 M CH3NH3Cl (aq); (c) 0.20 M CH3COOH (aq); (d) 0.20 M C6H5NH2 (aq). Justify your ranking.

[Quade Albert 2J]

You can write the dissociation reactions for each of the compounds in water. That will allow you to find the [H3O+] and you can use that to solve for the pH using the equation pH= -log[H3O+]. Then you could use the pH to rank these compounds.

[Allison Peng 1D]

We know that HCl is a strong acid, so [hydronium] = [HCl] (initial), so you can find the pH from there.
CH3NH3Cl is a salt, and Cl- acts as a kind of spectator, so it doesn't change the pH. CH3NH3+ is the conjugate acid of a weak base (amine), so it will act acidic in water (it wants to return to its base form). You can calculate the pH for this by using ICE tables with the [CH3NH3+](initial) equaling the concentration of the salt.
CH3COOH is a weak acid (carboxylic acid), so you can find [hydronium] using ICE tables, and pH from there
C6H5NH2 is a weak base (amine), so you can also use ICE tables to first find [hydroxide] (since it is a base) and then find [hydronium] and pH from there.

[Aditya Desai 1A]

If you still need help, holler, and I can do the actual calculations