Acids, Bases, and Solutions
What to know
Expect questions on acid-base definitions (Arrhenius, Brønsted-Lowry, Lewis), strong versus weak acids, pH and pOH, buffers, titration, and solution concentration (molarity, dilution, solubility). You should compute pH from [H+], convert between pH and pOH using pH + pOH = 14 at 25 °C, and interpret titration curves and indicators.
Know that strong acids and bases dissociate completely, weak ones partially, and that conjugate acid-base pairs differ by one proton. Understand that buffers resist pH change by neutralizing added acid or base, and that equivalence point pH depends on the strength of the acid and base involved.
Traps
- Using pH + pOH = 14 outside 25 °C without noting the assumption.
- Forgetting dilution changes concentration but not moles of solute (M1V1 = M2V2).
- Assuming equivalence point is always pH 7; weak acid–strong base titrations end basic.
- Confusing strong with concentrated; a weak acid can be concentrated.
- Sign and log errors: pH = −log[H+], and a tenfold change in [H+] shifts pH by 1.
Worked example
Find the pH of 0.010 M HCl. HCl is strong, so [H+] = 0.010 M. pH = −log(0.010) = 2.00. For a 0.010 M NaOH solution, pOH = 2.00, so pH = 14.00 − 2.00 = 12.00.
Dilution rule: moles before = moles after, so M1V1 = M2V2.