Question

A solution containing \(1.0 \mathrm{M}\) each of \(\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}, \mathrm{Mg}\left(\mathrm{NO}_{3}\right)_{2}, \mathrm{AgNO}_{3}, \mathrm{Hg}\left(\mathrm{NO}_{3}\right)_{2}\) is being electrolysed using inert electrodes. The values of standard electrode potential are: \(\mathrm{Ag}^{+}\left|\mathrm{Ag}=0.80 \mathrm{~V}, \mathrm{Hg}^{2+}\right| \mathrm{Hg}=0.79 \mathrm{~V}\) \(\mathrm{Cu}^{2+}\left|\mathrm{Cu}=0.34 \mathrm{~V}, \mathrm{Mg}^{2+}\right| \mathrm{Mg}=-2.37 \mathrm{~V}\) With increasing voltage, the sequence of deposit of metals on the cathode will be (a) \(\mathrm{Ag}, \mathrm{Hg}, \mathrm{Cu}, \mathrm{Mg}\) (b) \(\mathrm{Mg}, \mathrm{Cu}, \mathrm{Hg}, \mathrm{Ag}\) (c) \(\mathrm{Ag}, \mathrm{Mg}, \mathrm{Cu}\) (d) \(\mathrm{Cu}, \mathrm{Hg}, \mathrm{Ag}\)

Short answer

The sequence of deposit of metals on the cathode with increasing voltage will be Ag, Hg, Cu, Mg (option a).

Step-by-step solution

Understand the Electrolysis Process

During electrolysis, cations migrate to the cathode to gain electrons (reduction). The electrochemical series dictates that the metal cation with the highest electrode potential will be reduced first.

Arrange Metals by Standard Electrode Potential

Order the given metals by their standard electrode potential (SEP) values in descending order. The higher the SEP, the easier it is for the metal's cation to be reduced.

Identify the Sequence of Deposition

Based on the sorted SEP values, the metal with the highest SEP will deposit first. The sequence will be: Ag (+0.80V) > Hg (+0.79V) > Cu (+0.34V) > Mg (-2.37V).

Key concepts

Standard Electrode Potential

When diving into the fascinating world of electrochemistry, the term 'standard electrode potential' (SEP) often arises. It refers to the measure of an individual electrode's ability to drive an electric current when it's part of an electrochemical cell. Think of it like a 'muscle strength' contest for metals in an electrolytic solution.

Under standard conditions, which are defined as 298 K temperature, 1 atm pressure, and 1M concentration, these potentials are measured versus a standard hydrogen electrode (SHE), which arbitrarily has zero volts. The standard electrode potential is crucial because it indicates how likely an ion is to be reduced and thus deposit on the electrode during electrolysis.

The higher the standard electrode potential, the greater the ability of the ion to gain electrons, hence it will reduce or 'plate out' onto the cathode first. This knowledge assists students in predicting the outcome of electrochemical processes, from corrosion to the charging of batteries.

Electrochemical Series

The order of metals and their respective ions in terms of standard electrode potentials is known as the electrochemical series. This series is paramount in predicting which metal will be deposited first during the electrolysis process.

If you consider the electrochemical series as a leaderboard, metals with a higher positive SEP score rank at the top. These 'top-ranked' metals have a stronger pull for electrons and are thus reduced before others. In easier terms, if the electrode potential is like our high jumper’s best jump, the electrochemical series is the leaderboard showing who jumped the highest.

How does it affect electrolysis?

During electrolysis, you would look at this leaderboard to figure out which metal is going to win the electron race and be deposited on the cathode first. It's essentially a sequence-order list that depends on SEP values, directing the flow of electrons and the deposition of metals.

Metal Deposition Sequence

Imagine a race where metals are competing to get to the finish line, which in this case, is the cathode of an electrochemical cell. The metal deposition sequence is the order in which competing metal ions reach the finish line and are reduced to form a solid metal coating on the cathode.

Different metals ‘run’ at different speeds due to their inherent electrode potentials. Those with higher potentials are like the sprinters - they're quick to gain electrons and reach the cathode first. Conversely, metals with lower potentials are more like marathon runners, slower and getting to the cathide later.

To predict the metal deposition sequence correctly, students must understand that it all boils down to the relative strengths of the contenders' SEP values. With the electrolysis of a solution containing multiple metal ions, you can determine the sequence by lining up the metal ions according to their SEP values from highest to lowest, just like the answer 'Ag, Hg, Cu, Mg' in our exercise.