Chemistry / Unit 10: Solutions, Acids and Bases
10.4 Acids and Bases
Notes
Acids and bases have been defined in different ways.
- Arrhenius: an acid makes $\text{H}^+$ in water (HCl); a base makes $\text{OH}^-$ in water (NaOH).
- Brønsted-Lowry: an acid is a proton ($\text{H}^+$) donor; a base is a proton acceptor. This includes bases without $\text{OH}^-$, like $\text{NH}_3$.
- Conjugate pairs differ by one $\text{H}^+$. In $\text{NH}_3 + \text{H}_2\text{O} \rightleftharpoons \text{NH}_4^+ + \text{OH}^-$, $\text{NH}_4^+$ is the conjugate acid of $\text{NH}_3$, and $\text{OH}^-$ is the conjugate base of $\text{H}_2\text{O}$.
- Strong acids ionize completely: HCl, HBr, HI, $\text{HNO}_3$, $\text{H}_2\text{SO}_4$, $\text{HClO}_4$. Weak acids ionize only a little: acetic acid, HF.
- Acids taste sour and turn blue litmus red; bases taste bitter, feel slippery and turn red litmus blue.
Practice
In $\text{HCl} + \text{H}_2\text{O} \rightarrow \text{H}_3\text{O}^+ + \text{Cl}^-$, which substance acts as a Brønsted-Lowry base?
Water accepts a proton from HCl to become $\text{H}_3\text{O}^+$.
What is the conjugate base of $\text{H}_2\text{SO}_4$?
Remove one $\text{H}^+$: $\text{H}_2\text{SO}_4 \rightarrow \text{HSO}_4^-$.
Which is a weak acid?
Acetic acid ionizes only partly in water; the others are strong acids.
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