Question

During electrolysis, the cations get discharged at cathode in \(\quad\) order of their discharge potential.

Short answer

Answer: During electrolysis, cations get discharged at the cathode in the order of their discharge potential. Cations with lower reduction potential (higher position in the electrochemical series) are more likely to be discharged at the cathode than those with higher reduction potential (lower position in the series). However, other factors such as concentration and nature of the electrolyte can also affect the order of discharge.

Step-by-step solution

Understanding Electrolysis

Electrolysis is a process in which electrical energy is used to cause a non-spontaneous redox reaction to occur. In electrolysis, an electrolyte (a substance that conducts electricity) is decomposed into its constituent elements by passing electric current through it. An external voltage is applied to the electrolytic cell, driving the redox reaction in the opposite direction it would naturally occur.

Cathode and Anode

During electrolysis, the oxidation process (loss of electrons) occurs at the anode, while the reduction process (gain of electrons) occurs at the cathode. Here, the cations (positively charged ions) are attracted to the cathode, and the anions (negatively charged ions) are attracted to the anode.

Discharge Potential of Cations

Discharge potential refers to the minimum potential difference that must be applied to an electrolytic cell for a particular ion to be discharged at an electrode. In this case, we are focusing on the discharge of cations at the cathode.

Order of Discharge Potential

During electrolysis, the cations get discharged at the cathode based on their discharge potential. The order in which cations are discharged is determined by their position in the electrochemical series (also known as the activity series or reactivity series). Generally, cations with lower reduction potential (higher position in the series) are discharged more readily at the cathode than those with higher reduction potential (lower position in the series). However, other factors such as concentration and nature of the electrolyte can also affect the order of discharge. In conclusion, during electrolysis, the cations get discharged at the cathode in the order of their discharge potential. Cations with lower reduction potential are more likely to be discharged at the cathode than those with higher reduction potential.

Key concepts

Discharge Potential

Discharge potential is a fundamental concept in the study of electrolysis, a chemical process where electrical energy is used to drive a chemical reaction that would not normally happen on its own. This potential represents the minimum electrical energy required to force cations, positively charged ions, to gain electrons and be reduced at the negative electrode, known as the cathode.

Understanding the concept of discharge potential is crucial for predicting which ions will be reduced during electrolysis. It's not just a 'first come, first served' basis; it's about the energy hierarchy. Ions with a lower discharge potential will receive electrons first because they require less energy to make that leap from ion to atom. This is because these ions are 'eager' to gain electrons and move towards a more stable state.

Students often falter in grasping this concept because it seems abstract. To simplify, imagine a line of people waiting for a free meal. The minimum price for a meal represents the discharge potential, and the first in line are those who can 'afford' it with the 'currency' they have—lower potential. The meal, in this case, is the completion of the electrolysis reaction.

Cathode and Anode

In the process of electrolysis, there are two main sites where reactions occur: the cathode and the anode. These terms may be confusing at first, but a simple association can help you remember them. The cathode is the negative electrode, and this is where the reduction (gain of electrons) takes place. In contrast, the anode is the positive electrode, and it's the site of oxidation (loss of electrons).

Why is this important? Because it's at these electrodes that ions in the electrolyte get transformed into new substances. Cations, the positive ions, are attracted to the cathode, while anions, the negative ions, make their way to the anode. Think of the cathode as a 'reduction station' where cations turn into neutral atoms or molecules by gaining electrons, and the anode as an 'oxidation station' for anions to release electrons and become neutral or part of molecules.

Remember, the names cathode and anode are not based on the charge of the ions that are attracted to them but on the type of reaction that occurs at each electrode. This distinction is vital for understanding the direction of electron flow and the transformations during electrolysis.

Electrochemical Series

The electrochemical series, also known as the activity or reactivity series, is a chart that scientists use to predict which cation will be discharged first during electrolysis. It ranks elements according to their standard electrode potentials—a measure of a substance's tendency to be reduced.

Elements at the top of this series, like lithium and potassium, have lower reduction potentials and are more eager to gain electrons, meaning they'll be reduced at the cathode first. On the other hand, elements towards the bottom, such as copper and silver, need a bit more convincing—more electrical energy—to give up their positive charge.

This series is absolutely essential for students to understand electrolysis outcomes. It's not just the identity of the ion that matters; it's their ranking in this electrochemical pecking order. The higher up the series, the more likely an element will strut its stuff at the cathode first. Students often get tripped up here when they assume 'more reactive' means 'more likely to lose electrons,' but in this case, it's the opposite—it's about the readiness to gain electrons and thus be reduced.