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Chapter 14 | Acid-Base Equilibria 767
Solving this equation gives:
From this we find:
Step 4. Check the work. The arithmetic checks; when 1.2 10−3 M is substituted for x, the result
= Ka.
Check Your Learning
What is in a 0.15-M solution of Al(NO3)3 that contains enough of the strong acid HNO3 to bring [H3O+] to 0.10 M?
Answer: 2.1 10−5 M
The constants for the different stages of ionization are not known for many metal ions, so we cannot calculate the extent of their ionization. However, practically all hydrated metal ions other than those of the alkali metals ionize to give acidic solutions. Ionization increases as the charge of the metal ion increases or as the size of the metal ion decreases.
14.5 Polyprotic Acids
By the end of this section, you will be able to:
• Extend previously introduced equilibrium concepts to acids and bases that may donate or accept more than one proton
We can classify acids by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:
Even though it contains four hydrogen atoms, acetic acid, CH3CO2H, is also monoprotic because only the hydrogen atom from the carboxyl group (COOH) reacts with bases:
Similarly, monoprotic bases are bases that will accept a single proton.
