Question

Out of the following metals that cannot be obtained by electrolysis of the aqueous solution of their salts are: 1\. Ag 2\. \(\mathrm{Mg}\) 3\. \(\mathrm{Cu}\) 4\. Al (a) 2,4 (b) 2,3 (c) 1,4 (d) All

Short answer

Option (a) 2,4: Mg and Al cannot be obtained by aqueous electrolysis.

Step-by-step solution

Understanding Electrolysis in Aqueous Solution

Electrolysis involves passing an electric current through an aqueous solution to decompose compounds into their elements. Not all metals can be extracted by electrolyzing their aqueous salt solutions due to their position in the electrochemical series.

Identifying Metals Extracted by Electrolysis

Metals such as Ag and Cu can be deposited from an aqueous solution of their salts because they are less reactive than water and can be reduced directly. However, highly reactive metals like Mg and Al will not be deposited because water is preferentially reduced to hydrogen gas.

Evaluating Choices Based on Reactivity

From the list, Ag and Cu can be obtained through aqueous electrolysis. In contrast, Mg and Al cannot be obtained as they are more reactive than water and need fused salt electrolysis to be extracted.

Choosing the Correct Option

Since Mg and Al cannot be obtained from their aqueous solutions, option (a) 2,4 is the correct choice.

Key concepts

Electrochemical Series

The electrochemical series, also known as the activity series, is a list of elements organized based on their standard electrode potentials. This series is crucial in predicting the ease with which metals are oxidized or reduced. In layman's terms, it helps understand which metals can be extracted from their solutions via electrolysis. Typically, metals higher up in the series are more reactive. They tend to lose electrons readily, making them less likely to be deposited from aqueous solutions. Understanding this series is essential for selecting the right method for metal extraction. Reactive metals such as magnesium (Mg) and aluminum (Al) appear higher in this series, meaning they prefer to oxidize rather than be reduced in aqueous solutions. On the other hand, metals like silver (Ag) and copper (Cu) lie lower in the series. They are less reactive, so they can be easily deposited from aqueous solutions, as they will prefer reduction over oxidation when exposed to an electric current.

Aqueous Solution Electrolysis

Aqueous solution electrolysis is a method where water-based solutions are subjected to an electric current to separate them into different elements or compounds. This process is widely used for extracting metals, especially from their salt solutions. However, its effectiveness depends heavily on the reactivity of the metal ions in the solution. One key concept here is the competition between metal ions and water molecules for electrons. In the presence of a strong electric current, the less reactive metals in the solution will gain electrons from the cathode and form solid metal deposits. This is why metals like Ag and Cu can be extracted because they readily accept electrons due to their lower reactivity compared to water. Conversely, highly reactive metals, such as Mg and Al, don’t easily gain electrons in an aqueous environment. Instead, the water will typically be reduced to hydrogen gas before these reactive metals can deposit. This limitation highlights why not all metals can be obtained through this method and often require alternative processes like fused salt electrolysis.

Metal Reactivity

Metal reactivity is a fundamental concept in chemistry that reflects how a metal will behave in a chemical reaction. It often determines the best method of extraction for metals, specifically whether they can undergo electrolysis in aqueous solutions. Metals are ranked by their tendency to lose electrons or oxidize, known as reactivity. Highly reactive metals such as Mg and Al can easily lose electrons and form positive ions. This property makes it challenging to reduce them in aqueous solutions because water itself is a strong oxidizing agent when an electrical current is applied. In contrast, less reactive metals like Ag and Cu do not lose electrons willingly. They prefer reduction, meaning they can gain electrons more easily and precipitate from an aqueous solution under electrolysis. This difference in reactivity is a key factor in guiding metallurgists and chemists in the selection of processes for metal extraction, ensuring efficiency and feasibility.