What are Acids, Bases, and Buffer Solutions?
Acids and bases are opposite chemical species that define solution acidity. Buffers are special mixtures—weak acids plus their conjugate bases, or weak bases plus conjugate acids—that resist sudden pH changes.
Acids donate protons (H⁺) and have pH < 7; bases accept protons and have pH > 7. Buffers contain a weak acid–conjugate base pair (or weak base–conjugate acid pair) and resist pH shifts when small amounts of acid or base are added.
- •pH < 7
- •Sour taste
- •Turn litmus red
- •Donate H⁺
- •pH > 7
- •Bitter taste
- •Turn litmus blue
- •Accept H⁺
Step-by-step worked examples
Hydrochloric acid (HCl) is a strong acid. If 0.01 M HCl solution is prepared, what is its approximate pH?
[H⁺] = 0.01 M = 10⁻² M pH = -log[H⁺] = -log(10⁻²) = 2 Solution is strongly acidic
A buffer is made with 0.1 M acetic acid (CH₃COOH) and 0.1 M sodium acetate (NaCH₃COO). A small amount of HCl is added. Does pH change drastically?
The acetate ion (CH₃COO⁻) from the salt neutralizes added H⁺ CH₃COO⁻ + H⁺ → CH₃COOH pH drops only slightly, not drastically Buffer resists pH change
Sodium hydroxide (NaOH) is a strong base with concentration 0.001 M. Find [OH⁻] and pOH.
[OH⁻] = 0.001 M = 10⁻³ M pOH = -log[OH⁻] = -log(10⁻³) = 3 At 25°C: pH = 14 − 3 = 11
Flashcards
Quick quiz
Q1.Which compound is an acid?
Q2.A buffer contains 0.1 M weak acid and 0.1 M its conjugate base. What happens if acid is added?
Q3.Which is true about strong acids?
Q4.A buffer system requires…
The full card deck, worked steps and AI-tutor support for “What are Acids, Bases, and Buffer Solutions?” are in Notek — study by hand before your exam.
Common mistakes
All acids smell sharp, all bases smell nothing. — Correct: Some acids (like acetic) have odors; some bases (like ammonia) are pungent. Never smell chemicals.
A buffer means the pH never changes. — Correct: A buffer resists large changes, but the pH still shifts slightly when acid or base is added.
Strong acids are better buffers. — Correct: Buffers work best with weak acids or bases because they partially ionize.
Water is neutral, so it cannot become acidic. — Correct: Water is neutral only when pure; adding acid or base changes its pH immediately.
FAQ
What is the difference between acids and bases?
Acids donate protons (H⁺) and have pH < 7; bases accept protons and have pH > 7. At pH = 7 (neutral), [H⁺] = [OH⁻].
What is a buffer solution used for?
Buffers keep pH stable in chemistry, biology (blood), and pharmaceuticals by resisting acid–base additions.
Can a buffer work forever?
No—buffers have a capacity limit. Once all the weak acid or base is consumed, the buffer fails and pH changes rapidly.
What are everyday examples of buffers?
Blood (buffered by H₂CO₃/HCO₃⁻), soil, and milk all contain buffering systems.