Electrolysis Experiments

First pass

Melt the compound and its two ions become mobile, so a current can pass. Opposite charges steer them: the metal ion reaches the cathode and turns into metal, the non-metal ion reaches the anode and turns into the non-metal, as lead(II) bromide shows with grey lead and brown bromine.

Analogy — Think of a sorting gate at a recycling plant: metal pieces roll one way, non-metal pieces the other, and the two collection bins fill with pure, separate products.

Exam pointer — Describe the method with its equipment words: crucible, heat until molten, two graphite rod electrodes, and a power pack; the observation words are bubbling brown gas and grey deposit.

Going deeper

The experiment works because the molten state removes the lattice constraint: freed ions carry the current, so the melt undergoes electrolysis and decomposes into its elements. Charge decides where each ion ends up, with positive ions gaining electrons at the cathode to form the metal and negative ions losing electrons at the anode to form the non-metal.

Analogy — Picture two exits from a crowded hall, one marked plus and one marked minus: everyone walks to the exit opposite to their ticket, and each exit turns its crowd into a single pure product.

Exam pointer — Product questions reduce to one move: identify the two ions, send the positive one to the cathode and the negative one to the anode, then name the element each becomes.

First pass

The water itself donates H+ and OH- ions, so the electrolyte holds two rival sets of ions. Reactivity picks the winners: at the anode the halide wins if there is one, otherwise oxygen forms, and at the cathode hydrogen wins unless the metal is less reactive than hydrogen.

Analogy — Think of two queues for one ride: the queue that gets priority is decided by a fixed rule, and the losing queue simply waits in the solution for another turn.

Exam pointer — Write down every ion present before predicting anything; the exam hint says listing the ions first is the reliable route to the products.

Going deeper

The aqueous electrolyte is a mixture of compound ions and the ions from water's own split into H+ and OH-. Discharge follows relative reactivity: halide ions outrank hydroxide at the anode, producing the halogen, while at the cathode the less reactive candidate is discharged, so hydrogen emerges unless a metal less reactive than hydrogen is present.

Analogy — Picture a dispatch office sending the least stubborn claimant first: reactivity is stubbornness, and the particle that gives up most easily is the one released at the electrode.

Exam pointer — Practise the three named solutions to the point of instant recall: sodium chloride, dilute sulfuric acid and copper(II) sulfate, each with its own cathode and anode products.