Test: Eletrolysos of Aqueous Solutions - Year 11 MCQ

The concentration of the solution plays a crucial role in determining which ion is discharged during electrolysis. In a concentrated halide solution, the halogen forms at the anode, while in a dilute halide solution, oxygen is formed. This phenomenon occurs because the concentration affects the ease with which different ions are discharged at the electrodes. For example, in a concentrated solution of barium chloride, chlorine gas is produced at the anode as Cl- ions are discharged more readily than OH- ions. Conversely, in a dilute solution of barium chloride, oxygen is formed at the anode since only the OH- ions are discharged. Hence, concentration is a key factor influencing the outcome of electrolysis reactions.

The reactivity series of metals serves to rank metals in order of their reactivity. This series is vital in understanding how metals behave in various chemical reactions and electrolysis processes. It provides a systematic way to predict the behavior of different metals when they come into contact with other substances. By knowing the reactivity series, one can predict which metals will displace others in chemical reactions based on their relative reactivity levels.

Oxygen will be formed at the anode during electrolysis in a dilute solution of barium chloride. This occurs because in dilute solutions, only the OH- ions are discharged, leading to the formation of oxygen. Unlike in concentrated solutions where the halogen is formed at the anode, the presence of a dilute solution alters the outcome of the electrolysis process, favoring the production of oxygen gas.

At the negative electrode (cathode) during electrolysis of aqueous solutions, positively charged H and metal ions are attracted. Only one of these ions will gain electrons, leading to the production of either hydrogen gas or metal at the cathode. If the metal is higher in the reactivity series than hydrogen, hydrogen gas will be produced. Bubbling is observed at the cathode due to the release of hydrogen gas. The more reactive metal ions will remain in the solution, causing the discharge of the ions of the less reactive metal. Hence, unless the positive ions from the ionic compound are less reactive than hydrogen, hydrogen gas will be produced at the cathode.

When halide ions (chloride, bromide, iodide) and hydroxide ions are present during the electrolysis of aqueous solutions, the halide ion is discharged at the positive electrode (anode). It loses electrons and forms a halogen gas such as chlorine, bromine, or iodine. This process occurs because the halide ions are discharged more readily than the hydroxide ions in this scenario. It is essential to consider the relative reactivity of the ions present in the solution to determine which one will be discharged at the electrode.

In the electrolysis of copper(II) sulfate, the inert graphite electrodes play a crucial role in allowing the discharge of less reactive ions. Since copper is less reactive than hydrogen, copper ions are discharged at the cathode. This happens because the less reactive ion is preferentially discharged at the electrode. Graphite electrodes do not react in the electrolysis process, which is why they are used in this setup. This ensures that the reactions occur at the electrodes without the electrodes themselves being consumed in the process.

The mass gain at the cathode during the electrolysis of copper(II) sulfate is due to the reduction of copper ions. This reduction process involves the conversion of copper ions (Cu2+) into copper atoms, which are then deposited onto the cathode. This phenomenon is a result of the transfer of electrons and the subsequent reduction reaction occurring at the cathode.

The observation that the gain in mass at the negative electrode equals the loss in mass at the positive electrode during electrolysis demonstrates the principle of conservation of mass in the electrolysis process. This observation confirms that the amount of substance deposited at the cathode is equal to the amount of substance lost at the anode, highlighting the law of conservation of mass in chemical reactions.

The primary reason for the reduction of copper ions at the cathode during electrolysis is to form copper atoms. This reduction process involves the gain of electrons by copper ions (Cu2+), leading to the formation of solid copper atoms that are then deposited onto the cathode. This reduction reaction is essential for the electroplating of copper and other related processes.

The concentration of Cu2+ ions in the solution remains constant during the electrolysis of copper(II) sulfate because of the equivalence between the amount of copper deposited on the negative electrode and the copper ions lost from the positive electrode. This balance ensures that the overall concentration of Cu2+ ions in the solution remains unchanged, maintaining the electrolyte's composition throughout the electrolysis process.