How does a buffer work?

A buffer contains a weak acid and its conjugate base. The base catches added H₃O⁺, the acid catches OH⁻. Only the ratio of the two forms changes, so the pH shifts little.

What is the buffer range?

The buffer range is the pH range pKa ± 1. There the ratio c(A⁻) : c(HA) lies between 1 : 10 and 10 : 1. Outside it, one of the two forms is nearly used up.

What is buffer capacity?

It describes how much strong acid or base a buffer can catch before the pH changes markedly. It rises with total concentration: twice the amount means twice the capacity at the same pH.

What does the app show about blood buffering?

The bicarbonate system with pKa′ = 6.1 at 37 °C, 24 mmol/L HCO₃⁻ and 1.2 mmol/L CO₂, giving pH 7.40. You switch the lungs and see: 0.5 mmol of acid lowers the pH to 7.30 when open and to 6.59 when closed.

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Buffer Lab

About this app

Drag drops straight into the beaker: acetic acid/acetate, ammonium/ammonia, phosphate or bicarbonate in blood catch H₃O⁺ and OH⁻ particle by particle until the reserve is used up. Comparison beaker with pure water, buffer curve, buffer range pKa ± 1, capacity bar, exact calculation and exam tasks.

With explain mode: an AI tutor walks you through the app, points out what matters in the scene and answers your questions.

What it is about

A buffer solution contains a weak acid HA and its conjugate base A⁻. Added oxonium ions react with A⁻ to form HA, hydroxide ions react with HA to form A⁻. According to the Henderson–Hasselbalch equation pH = pKa + log(c(A⁻)/c(HA)), the pH depends only on the ratio and therefore changes little. That holds as long as both forms are plentiful. The buffer range is taken as pKa ± 1. Once the reserve is used up, the capacity is exhausted and the pH falls or rises steeply.

What the app shows

HA and A⁻ appear in the beaker as particles, one particle stands for 0.1 mmol. Every drop of hydrochloric acid or sodium hydroxide also falls into a comparison beaker with pure water. There the pH jumps at once; in the buffer the ions fly to a partner and convert it. The buffer curve grows along, and the capacity bar shows the reserve. The calculation uses the full charge balance with all protolysis steps and the volume increase.

What you can try

Prepare acetic acid/acetate, ammonium/ammonia, dihydrogen phosphate/hydrogen phosphate or carbonic acid/bicarbonate in blood, and change the ratio and total concentration. Drag drops into the beaker or hold the pipette down. For blood you switch the lungs between open and closed. In the task section you place a marker on the curve: how much more can the buffer take, what pH does it reach, which pair suits a target pH? The feedback shows the calculation.

Frequently asked questions

How does a buffer work?: A buffer contains a weak acid and its conjugate base. The base catches added H₃O⁺, the acid catches OH⁻. Only the ratio of the two forms changes, so the pH shifts little.
What is the buffer range?: The buffer range is the pH range pKa ± 1. There the ratio c(A⁻) : c(HA) lies between 1 : 10 and 10 : 1. Outside it, one of the two forms is nearly used up.
What is buffer capacity?: It describes how much strong acid or base a buffer can catch before the pH changes markedly. It rises with total concentration: twice the amount means twice the capacity at the same pH.
What does the app show about blood buffering?: The bicarbonate system with pKa′ = 6.1 at 37 °C, 24 mmol/L HCO₃⁻ and 1.2 mmol/L CO₂, giving pH 7.40. You switch the lungs and see: 0.5 mmol of acid lowers the pH to 7.30 when open and to 6.59 when closed.

Subject: Chemistry

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