# Electrolysis of dilute aqueous solutions

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In summary, electrolysis is a process that involves passing an electric current through a solution to cause a chemical reaction. Dilute aqueous solutions are solutions with low concentrations of dissolved substances. Electrolysis works by using electrodes to attract ions and cause a reaction. Some common applications of electrolysis of dilute aqueous solutions include metal extraction and water purification. The rate of electrolysis can be affected by factors such as concentration, electrode size, voltage, current, and temperature.
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## Homework Statement

If dilute, aqueous magnesium bromide is electrolyzed, one product is formed at each electrode. Identify the product, state the electrode it occurs at (anode or cathode) and state a reason for your choice of product.

## Homework Equations

Mg2+(aq) + 2e- --> Mg(s) E°red = -2.37 V

0.5 Br2(l) + e- --> Br-(aq) E°red = +1.07 V

H2O(l) + e- --> 0.5 H2(g) + OH-(aq) E°red = -0.83 V

0.5 O2(g) + 2H+(aq) + 2e- --> H2O(l) E°red = +1.23 V

## The Attempt at a Solution

At the cathode hydrogen gas and OH- ions would be formed since the reduction potential of water is less negative than the reduction potential of magnesium. This makes it easier to reduce water at the cathode.

At the anode, oxidation occurs so the equations and potentials for the anions will have to be flipped.

Br-(aq) --> 0.5 Br2(l) + e-ox = -1.07 V

H2O(l) --> 0.5O2(g) + 2H+(aq) + 2e-ox = -1.23 V

It would appear that it is easier to oxidize bromine ions since the oxidation potential is less negative. However, the solution is dilute. In the equilibrium equation

0.5 Br2(l) + e- <--> Br-(aq)

The equilibrium would shift to the right and the number of electrons would be reduced. This would make the standard reduction potential of bromine more positive and hence the standard oxidation potential would be more negative. Since the oxidation potentials of bromine and water are close together, the bromine solution being dilute would cause water to be easier to oxidize instead of bromine (similar to how concentrated chlorine is oxidized over water in the electrolysis of brine). Thus oxygen gas and H+ ions are formed at the anode.

However, my teacher said that bromine would still be oxidized regardless. Can anyone please tell me what is wrong with my argument?

Last edited:

Your argument is correct in terms of the standard reduction potentials and the effect of dilution on the equilibrium. However, in practical electrolysis, other factors such as concentration, temperature, and pH can also play a role in determining the products formed at the electrodes. In this case, the concentration of magnesium bromide and the pH of the solution may also influence the products formed.

Additionally, the electrolysis process involves the passage of current through the solution, which can cause changes in the concentrations of the ions and thus affect the equilibrium. This can lead to a different product being formed at the anode compared to what is predicted based on the standard reduction potentials.

In summary, while your argument is valid in terms of the theoretical principles, it is important to consider other factors that may affect the products formed in practical electrolysis.

## 1. What is electrolysis?

Electrolysis is a process in which an electric current is passed through a solution, causing a chemical reaction to occur.

## 2. What are dilute aqueous solutions?

Dilute aqueous solutions are solutions in which a small amount of a substance is dissolved in water. These solutions have a low concentration of the dissolved substance.

## 3. How does electrolysis work?

In electrolysis, an electric current is passed through the solution using electrodes. The positive electrode is called the anode and the negative electrode is called the cathode. The electric current causes the ions in the solution to move towards the electrodes, where they either gain or lose electrons, resulting in a chemical reaction.

## 4. What are some common applications of electrolysis of dilute aqueous solutions?

Electrolysis of dilute aqueous solutions is commonly used in industries such as metal extraction, water purification, and production of chemicals and fuels. It is also used in scientific research for various experiments and studies.

## 5. What are some factors that affect the rate of electrolysis?

The rate of electrolysis can be affected by factors such as the concentration of the solution, the size of the electrodes, the voltage and current used, and the temperature of the solution. Higher concentrations, larger electrodes, and higher voltage and current can all increase the rate of electrolysis. Higher temperatures can also increase the rate of electrolysis, but can also cause the solution to evaporate faster.

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