# Using Pourbaix diagrams to calculate corrosion in water

• Chemistry
• wnvl2
In summary, the conversation discusses using a Pourbaix diagram to determine the stability of copper at pH 8 and the potential range at which it will corrode. It also mentions using an SHE connected via a salt bridge to measure the potential in an experimental situation. The potential values on the diagram are affected by the presence of oxygen and pH. The question posed is whether copper will corrode in a water solution without oxygen, and the answer is that it will still corrode at potentials above 0.1V.
wnvl2
Homework Statement
Which of the metals Al, Cu, Fe, Ag, Pb and Au can (thermodynamically) corrode in water that is Slightly acidic (pH = 6) (AI, Cu, Fe, Ag, Pb) Slightly basic (pH = 8) (AI, Cu, Fe, Pb) Very acidic (pH = 1) (AI, Cu, Fe, Ag, Pb) Very basic (pH = 14) (AI, (Cu), Fe, Pb) . .
Relevant Equations
Use Pourbaix diagram

Let us solve it for Cu at pH =8. I found this Pourbaix diagram. What is the electrochemical potential I should use to check that Cu is there the stabel form. Should I check for all values of E between the blue lines at pH = 8? How can I measure the E value in reality?

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In the case of pH 8, your task is pretty easy. But in general, the Pourbaix diagram will give you the potentials/pH’s over which different forms of a metal are stable in water (usually).

As for what the potential is in an experimental situation, it’s either chosen by you when you apply a voltage or it can be measured straightforwardly by a potentiometer.

Astronuc and wnvl2
If I am right, I can connect the copper to a SHE, measure the voltage and that is the E I have to use in the Pourbaix diagram. As the E is not specified in the original question, I can not give a unique answer.

wnvl2 said:
As the E is not specified in the original question, I can not give a unique answer.
You should try to answer the question nonetheless.

I'll try to frame the question somewhat more clearly. For your example, copper at pH=8, over what range of potential will it corrode?

Astronuc
What it is that is present everywhere and makes metals corrode?

Oxygen?

Combined with pH it should give you some idea about the potentials involved.

Not that they are ignored on the diagram.

Does that mean that if the copper is in a water solution in abscence of oxygen that the copper will not corrode?

wnvl2 said:
Does that mean that if the copper is in a water solution in abscence of oxygen that the copper will not corrode?
I’m not sure what borek is getting at, but this is definitely not true. Did you try answering my question in post 5?

Above 0.1V there is oxidation. Below 0.1V cupper is stable.

TeethWhitener
Great! Can you figure out the rest of the question now?

In fact it is not an assignment I have to submit, but I think the policy is that I put this kind of questions here. I am even not a student in chemistry, I just try to understand it. The solution of the exercice is clear. You look up the pH, you draw a vertical line. You see for which E the metal is stable. The E can be measured with an SHE connected via a salt bridge with the water around the metal.

TeethWhitener

## 1. How do Pourbaix diagrams help in calculating corrosion in water?

Pourbaix diagrams are graphical representations of the thermodynamic stability of different chemical species in a given system. By plotting the potential (E) and pH values for different chemical species, these diagrams can help determine the most stable form of a particular element in a specific environment. This information can then be used to predict the likelihood of corrosion occurring in that environment.

## 2. What factors affect the accuracy of corrosion calculations using Pourbaix diagrams?

The accuracy of corrosion calculations using Pourbaix diagrams can be affected by several factors, including the accuracy of the thermodynamic data used to construct the diagram, the temperature and pressure of the system, and the presence of other chemical species that may interact with the metal being studied.

## 3. Can Pourbaix diagrams be used for all types of corrosion?

Pourbaix diagrams are most commonly used for aqueous corrosion, as they are specifically designed to analyze the stability of chemical species in water. However, they can also be used for other types of corrosion, such as high-temperature oxidation, as long as the appropriate thermodynamic data is available.

## 4. How can Pourbaix diagrams be used to prevent corrosion?

By using Pourbaix diagrams to predict the conditions under which corrosion is likely to occur, engineers and scientists can design materials and systems that are more resistant to corrosion. This can include selecting materials with a more stable thermodynamic state in the given environment, or adjusting the pH or potential of the system to make it less corrosive.

## 5. Are there any limitations to using Pourbaix diagrams for corrosion calculations?

While Pourbaix diagrams are a useful tool for predicting corrosion, they have some limitations. They are based on thermodynamic data, which may not always accurately reflect real-world conditions. Additionally, they do not take into account kinetic factors, such as the rate of corrosion, which can also play a significant role in the corrosion process.

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