Atoms and Ions: Electrolysis of Aqueous Solution
Atoms and Ions: Electrolysis of Aqueous Solution
- Understand that atoms make up everything in the world. They consist of a nucleus at the center —which contains protons and neutrons— and electrons that orbit this nucleus.
- Get familiar with the term ion: an atom or group of atoms that has lost or gained one or more electrons, thus acquiring a charge. Positive ions have lost electrons, and negative ions have gained them.
- Electrolysis involves using an electric current to cause a chemical change. This electric current is often used to cause a substance to decompose.
- When an ionic substance is melted or dissolved in water, its ions are free to move about within the liquid. These moving ions can conduct electricity and facilitate electrolysis.
- Electrolysis of an aqueous solution involves two half-reactions: oxidation at the anode (positive electrode) and reduction at the cathode (negative electrode).
- Oxidation is a loss of electrons, while reduction involves a gain of electrons. Remember this using the mnemonic “OIL RIG”: Oxidation Is Loss, Reduction Is Gain.
- In the electrolysis of aqueous solutions, water can also be split into hydrogen and oxygen. Hydrogen forms at the cathode and oxygen at the anode.
- Nitrate, sulfate and halide ions are usually present in the electrolytes. While nitrate and sulfate ions remain in the solution, halide ions can be discharged at the anode under suitable conditions.
- Predicting the products of electrolysis for aqueous solutions may be complex, as it requires you to consider both the metal ions and the hydroxide ions from the water. The product depends on the reactivity of the metal involved.
- Usually, if the salt contains a reactive metal (like potassium, sodium or calcium), then hydrogen gas is given off at the cathode, rather than the metal. Otherwise, the metal is deposited at the cathode.
- For the anode, if halide ions are present, they will be discharged to give chlorine, bromine or iodine. If they are not, then the hydroxide ions from the water are discharged to give oxygen.
- It’s important not just to understand how electrolysis works, but also its practical applications, such as the extraction of metals from their ores, electroplating, and the manufacturing of chemicals.