Practical skills Study Guide

An electrochemical cell is a device that uses a chemical reaction to produce electrical energy, or uses electrical energy to drive a non-spontaneous chemical reaction. When we talk about electrolysis, we are referring to the second case: using electrical energy to break down an ionic compound, either molten or in solution. This process requires a direct current (DC) power supply, two electrodes (an anode and a cathode), and an electrolyte.

The electrolyte is the ionic compound that conducts electricity when molten or dissolved in a solvent, allowing ions to move and carry charge. The electrodes are typically made of inert materials like graphite or platinum, which conduct electricity but do not react themselves throughout the electrolysis. The anode is the positive electrode where oxidation (loss of electrons) occurs, and anions (negatively charged ions) are attracted to it. The cathode is the negative electrode where reduction (gain of electrons) occurs, attracting cations (positively charged ions).

During electrolysis, specific products are formed at each electrode. Identifying these products is crucial and often involves simple qualitative tests. For instance, if hydrogen gas is produced at the cathode, it can be identified by the 'squeaky pop' test using a lit splint. Chlorine gas, produced at the anode, can be identified by its characteristic pale green colour and its ability to bleach damp litmus paper. Oxygen gas, also produced at the anode in some cases, relights a glowing splint. Metal deposits are typically solid and can be seen forming on the cathode. Halogens (like bromine or iodine) can be identified by their distinctive colours. Safety is paramount when conducting electrolysis experiments, especially due to the potential generation of flammable gases (hydrogen) or toxic gases (chlorine). Proper ventilation and personal protective equipment are essential.

Distillation is a separation technique used to separate a soluble solid from a liquid (simple distillation) or two miscible liquids with different boiling points (fractional distillation). In the context of separating a liquid mixture, simple distillation is often used when one component is significantly more volatile (has a lower boiling point) than the other, or to separate a pure liquid from a solution containing non-volatile solutes. The basic principle involves heating the mixture until the component with the lower boiling point vaporises. This vapour then travels through a condenser, which is cooled by circulating water, causing the vapour to condense back into a liquid. This purified liquid, called the distillate, is collected in a separate beaker or flask. The component with the higher boiling point or the non-volatile solid remains in the original flask. Careful control of heating is crucial to ensure efficient separation and prevent bumping. Measuring the temperature of the vapour is essential to confirm that the desired component is boiling and condensing. The apparatus typically includes a distillation flask, a Bunsen burner (or electric heater for flammable liquids), a thermometer, a condenser, and a receiving flask. Proper assembly ensures that the thermometer bulb is positioned correctly at the level of the side arm leading to the condenser, and that cooling water enters the condenser at the lowest point and exits at the highest to maximise cooling efficiency. This method allows for the collection of a relatively pure sample of one component from a mixture, making it a valuable technique in chemistry.