Study guides › C/P › General Chemistry
Buffers & Titrations
Buffers hold pH steady and titrations measure how much acid or base a sample holds. You will use Henderson-Hasselbalch, read titration curves region by region, and choose an indicator for any acid-base pairing.
Study this chapter in PrepMed (free)
What this chapter covers
- Buffers & the Henderson-Hasselbalch Equation. One equation, pH = pKa + log(base/acid), solves most buffer questions on the MCAT, including blood pH.
- Buffer Capacity, Range & Preparation. Knowing where a buffer works best, and how far it can be pushed, lets you pick and build the right one.
- Titration Curves: Strong and Weak. Titration curves appear on the MCAT constantly. Learn the four regions and where pKa and equivalence sit.
- Indicators & Polyprotic Titrations. Choose an indicator by matching its color-change range to the steep part of the curve, and expect one jump per proton.
Key points to know
- Buffer = weak acid plus conjugate base in comparable amounts
- pH = pKa + log([A⁻]/[HA]); equal amounts give pH = pKa
- Effective buffer range is pKa ± 1
- Capacity is greatest at pH = pKa and rises with concentration
- Equivalence: moles acid = moles base; strong/strong is pH 7
- Weak acid + strong base: equivalence pH > 7; weak base + strong acid: < 7
- Indicator changes color over pKa(In) ± 1; endpoint should sit on the steep part
- Weak acid + strong base: phenolphthalein; weak base + strong acid: methyl red or orange
Try a practice question
Which mixture is a buffer?
- HCl and NaCl
- CH₃COOH and CH₃COONa
- NaOH and NaCl
- HNO₃ and NaNO₃
Show the answer
B. A buffer needs a weak acid with its conjugate base. Acetic acid and acetate qualify. HCl and HNO₃ are strong acids, whose conjugate bases (Cl⁻, NO₃⁻) do not accept protons, and NaOH is a strong base.
Common questions
What does this chapter cover?
Buffers & Titrations covers Buffers & the Henderson-Hasselbalch Equation, Buffer Capacity, Range & Preparation, Titration Curves: Strong and Weak, Indicators & Polyprotic Titrations.
What should I know first?
Buffer = weak acid plus conjugate base in comparable amounts pH = pKa + log([A⁻]/[HA]); equal amounts give pH = pKa Effective buffer range is pKa ± 1
21 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.