A buffer holds its pH
"A buffer holds its pH" is a free, interactive Class 11 Chemistry simulation for NEET and JEE, built on the NCERT section "Buffer solutions" in Equilibrium. Acetic acid (or ammonia) is partly neutralised by strong base (acid) added in mmol; the titration curve, the mixture's composition and the Henderson–Hasselbalch pH are shown, and drops of HCl test the buffer against plain water. NEET has asked about this idea 3 times in 10 years of papers. JEE Main asked 52 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
From the lesson Buffer solutions in Equilibrium. Change the values and watch what happens.
What it shows
NCERT § "Buffer Solutions"
Acetic acid (or ammonia) is partly neutralised by strong base (acid) added in mmol; the titration curve, the mixture's composition and the Henderson–Hasselbalch pH are shown, and drops of HCl test the buffer against plain water.
Controls
4 to try
- Segmentedweak acid + NaOH / weak base + HCl
- Sliderstrong reagent added 0–5 mmol (weak species fixed at 3 mmol)
- Buttonadd 0.1 mmol HCl
- Togglebuffer / pure water
Try this
Mix 3 mmol NH3 with 1 mmol HCl and read the pH from pOH = pKb + log(1/2); then find the mix where pH = pKa exactly (half-neutralised).
Common mistake
Treating excess weak base + strong acid as a simple salt solution.
In NEET
10 years of papers
Asked 3 times in 10 years of NEET.
See the past questions: pH and Buffer Solutions, Equilibrium (chapter)
In JEE Main
42 shifts analysed
52 questions from Equilibrium across the 42 JEE Main shifts Lumi has analysed (2017–2026).
The idea behind it
NCERT § "Buffer Solutions"
- A buffer resists change in pH when small amounts of acid or base are added or when it is diluted.
- An acidic buffer is a weak acid with its salt of a strong base (acetic acid and sodium acetate); a basic buffer is a weak base with its salt of a strong acid (ammonia and ammonium chloride).
- pH of an acidic buffer: pH = pKa + log([conjugate base]/[acid]) (Henderson-Hasselbalch equation).
- pOH of a basic buffer: pOH = pKb + log([conjugate acid]/[base]), and pH = 14 − pOH at 298 K.
- When the acid and its conjugate base are present at equal concentrations, pH = pKa.
- A buffer can also be made by partly neutralising a weak base with a strong acid: mixing 3 mmol of NH₃ with 1 mmol of HCl leaves 2 mmol NH₃ and 1 mmol NH₄⁺, a basic buffer.
- Within a buffer only the ratio of amounts matters, so millimoles can be used directly without dividing by the total volume.
Questions
5 answers
- What does the "A buffer holds its pH" simulation show?
- Acetic acid (or ammonia) is partly neutralised by strong base (acid) added in mmol; the titration curve, the mixture's composition and the Henderson–Hasselbalch pH are shown, and drops of HCl test the buffer against plain water.
- What mistake does the "A buffer holds its pH" simulation fix?
- A common mistake it clears up: treating excess weak base + strong acid as a simple salt solution.
- Has NEET asked about this idea?
- Yes. NEET has asked about this idea 3 times in 10 years of papers.
- Does JEE Main ask questions from Equilibrium?
- Yes. JEE Main asked 52 questions from this chapter across the 42 shifts Lumi has analysed (2017–2026).
- Is this simulation free?
- Yes. It is free and runs in the browser on a phone or a laptop. It belongs to the lesson "Buffer solutions" in Equilibrium (Class 11 Chemistry).
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