Q.Explain what electrophoresis demonstrates about colloidal particles. In an electrophoresis experiment, a freshly prepared $\text{Fe(OH)}_3$ sol is found to migrate towards the cathode when an electric field is applied. What does this indicate about the charge on the sol particles?

[!TLDR] Electrophoresis shows colloidal particles are charged, since they migrate toward the electrode of opposite sign. [!ANSWER] $\text{Fe(OH)}_3$ sol migra …

Electrophoresis is the directed migration of colloidal particles through the dispersion medium under an applied electric field, and observing that migration occurs at all demonstrates that colloidal particles carry a net electric charge, acquired by selective adsorption of specific ions from the medium onto the particle surface. A particle migrates toward the electrode of opposite charge to its own — a positively charged particle moves toward the cathode (negative electrode), while a negatively charged particle moves toward the anode (positive electrode). Since the $\text{Fe(OH)}_3$ sol here migrates towards the cathode, its particles must carry a net positive charge (from prefere …

Recall that a particle migrates toward the electrode of opposite sign to its own charge, then infer the char …

Do not assume migration toward the cathode means the particle is negatively charged — opposite charges attract, so migration toward the cathode (th …