Strong vs Weak Acids – Same Concentration, What Differs?

What it shows

A strong acid such as HCl ionizes completely in water, while a weak acid HA ⇌ H⁺ + A⁻ ionizes only partly, as set by its Ka. At the same molar concentration a weak acid therefore has a much lower [H⁺], a higher pH, lower conductivity and reacts more slowly with magnesium. The model finds [H⁺] exactly from Ka and Kw, estimates conductivity from limiting molar conductivities and includes the magnesium salt formed, so the common-ion effect slows the weak acid as it reacts.

How to use

Choose a Weak acid and drag Concentration. Watch the magnifiers, the bulbs and the table of α, [H⁺], pH and conductivity. Press Add Mg to compare the bubbling and the graph of H₂ volume against time; raise Speed to finish sooner. Press Dilute 10× or switch Graph to degree of ionization, then drag across the graph to change the concentration.

Parameters you can change

• Weak acid compared with HCl CH₃COOH – ethanoic (acetic) acid (Ka = 1.75×10⁻⁵), HCOOH – methanoic (formic) acid (Ka = 1.8×10⁻⁴), HF – hydrofluoric acid (Ka = 6.8×10⁻⁴), HClO – hypochlorous acid (Ka = 3.0×10⁻⁸)
• Concentration of each acid 0.001–1 M
• Time speed 1× (real time), 5× faster, 20× faster, 100× faster
• Graph H₂ volume against time, Degree of ionization α against concentration

Questions to explore

1. Why is the bulb much dimmer in 0.1 M CH₃COOH than in 0.1 M HCl?
2. Do the two beakers finally give the same volume of hydrogen? Why?
3. By roughly what factor does α of CH₃COOH increase when it is diluted 100 times?