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Freundlich adsorption of acetic acid on charcoal: from a pH reading to the constant k

One continuous run on a single dashboard: weigh and dissolve the acid, add charcoal, shake until a third of the molecules are stuck to the surface, measure the pH, turn it into the equilibrium concentration with Ka, plot the isotherm and finish with k - the answer appearing only when the run concludes.

Sub-topics covered

• Adsorption from solution onto a solid
• Freundlich isotherm and its logarithmic form
• Slope and intercept of the log-log plot
• Weak-acid equilibrium and Ka
• pH and hydrogen-ion concentration
• Mass balance on the adsorbate

What it teaches

• Adsorption is a surface process, so nothing leaves the flask - the adsorbate only changes address
• A pH reading gives the hydrogen ion, not the weak acid that produced it
• Ka is the conversion factor between [H+] and the concentration of an undissociated weak acid
• The C in the Freundlich isotherm is the concentration left at equilibrium, never the initial one
• Taking logarithms turns a power law into a straight line whose gradient is 1/n and whose intercept is log k

Simulation ID

• ADV-2026-P2-CHE-Q11 · revision 2

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