Buffer capacity lab

CH₃COOH / CH₃COO⁻ · pK_a 4.74 · 1.00 L · every dose is one deliberate action

Make the buffer

Each dose goes into both beakers, so the comparison is controlled.

System: Dose

n(HA) 0.100 n(A⁻) 0.100

Buffer

0 doses absorbed

4.740 pH · started 4.740 no dose added yet

n(HA) 0.100 n(A⁻) 0.100

Add a dose and this line names the species that absorbed it.

Plain water

the same doses, no reservoir

7.000 pH · started 7.000 no dose added yet

There is no reservoir here. Every mole of added acid stays as free H⁺, so the pH is just −log[H₃O⁺] and it moves the whole way.

pH vs doses added

buffer water

±1 pH unit around the start pK_a, where capacity is greatest

Readouts

pH buffer4.740 pH water7.000 n(HA)0.100 mol n(A⁻)0.100 mol [A⁻]/[HA]1.000 pK_a4.74 volume1.00 L β (buffer, per litre)0.115 doses absorbed0

Ready. Add a strong-acid dose and compare the two beakers. The pH is solved from the full charge and mass balance every time, not from Henderson–Hasselbalch, so the curve stays right after a reservoir empties.