🧪 Buffers & Henderson-Hasselbalch

Buffers are solutions that resist pH change when small amounts of acid or base are added. They show up in both chemistry and biology questions on the DAT because understanding buffer systems is essential to many biochemical processes—like blood pH regulation.

🧠 How Buffers Work on the DAT

Buffers:

• Consist of a weak acid + conjugate base or weak base + conjugate acid

• Resist pH changes when H⁺ or OH⁻ is added

• Are most effective when pH ≈ pKa (i.e., when [A⁻] ≈ [HA])

📈 Quick Buffer Summary Table

Term	Meaning
pKa	Strength of the weak acid
[A⁻] / [HA] ratio	Controls the pH level
Best buffering range	pKa ± 1
Buffer capacity	How well a buffer resists change

💬 Common DAT Questions You Might See

You’re given pKa = 4.76 and concentrations of [A⁻] = 0.2 M, [HA] = 0.2 M. What’s the pH?

✅ Answer:

pH = 4.76 + log (0.2 / 0.2) = 4.76

Other formats include:

• Graphical analysis of buffer zones

• Describing effects of strong acid/base addition

• Titration curve labeling with buffer regions

🔁 DAT Tips for Buffer Mastery

• When [A⁻] = [HA], pH = pKa

• When [A⁻] > [HA], pH > pKa

• When [A⁻] < [HA], pH < pKa

• Use the log rules: log(1) = 0, log(10) = 1, log(0.1) = -1

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✅ Summary

• Buffers resist pH change via weak acid/base equilibrium.

• Henderson-Hasselbalch helps you calculate buffer pH quickly.

• Expect to see this in conceptual and math-based DAT chemistry questions.

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