PH of concentrated and dilute acids

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In summary: It would have a pH of 1.0!pH is a measure of the concentration of hydrogen ions in a solution.Think about pure sulfuric acid - simple logic tells us it should be highly acidic. Well, if it is pure, there is no water at all! What water solution, when there is no water? It would have a pH of 1.0!
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Betadine
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Homework Statement



I understand that pH is a measure of the concentration of hydrogen ions in a solution.

A more concentrated acid would have more hydrogen ions in a given volume of solution? Wouldn't that mean that it should have a much lower pH?

Why then do we have the pH of dilute acids being lower?
 
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Can you give examples? It is possible you refer to the way activity coefficients behave in high ionic strength solutions, but I would prefer to know what we are talking about before going into details.
 
  • #3
Borek said:
Can you give examples? It is possible you refer to the way activity coefficients behave in high ionic strength solutions, but I would prefer to know what we are talking about before going into details.

Thank you for the reply, Borek :smile:

I am not too sure actually.

My thoughts are based on the pH of dilute hydrochloric acid. It's 1.0, which is very low.

Could it be that the pH of concentrated hydrochloric acid is lower than 1.0?

In other words, maybe for a particular named acid, its concentrated version will always have a lower pH than its dilute solution? Sorry, I am confused and just jumping to conclusions. Hehe.
 
  • #4
Betadine said:
Could it be that the pH of concentrated hydrochloric acid is lower than 1.0?

Yes, it can even get negative.

In very concentrated solutions things get complicated. Our methods of pH calculation (and to some effect measurement) assume ions don't interact too strongly as they are separated by copious amounts of water. When there is not enough water molecules, these assumptions no longer work, and rather unexpected things start to happen.

pH is a measurement of H+ activity in water solution. Think about pure sulfuric acid - simple logic tells us it should be highly acidic. Well, if it is pure, there is no water at all! What water solution, when there is no water?
 
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You are correct in your understanding that pH is a measure of the concentration of hydrogen ions in a solution. A more concentrated acid does indeed have a higher concentration of hydrogen ions in a given volume of solution, resulting in a lower pH. However, when we compare the pH of concentrated and dilute acids, it is important to consider the concept of acid strength. The strength of an acid refers to its ability to dissociate and release hydrogen ions in a solution. Dilute acids, even though they may have a lower concentration of hydrogen ions, can still be considered strong acids if they have a high degree of dissociation. This means that they are able to release a higher percentage of their hydrogen ions into the solution, resulting in a lower pH. On the other hand, concentrated acids may have a higher concentration of hydrogen ions, but if they are not as strong and have a lower degree of dissociation, their pH may not be as low as a dilute acid. Therefore, the pH of an acid is not solely determined by its concentration, but also by its strength.
 

What is the difference between concentrated and dilute acids?

Concentrated acids have a higher concentration of acid molecules in a given volume, while dilute acids have a lower concentration of acid molecules in the same volume.

How does the pH of concentrated and dilute acids compare?

The pH of concentrated acids is lower (more acidic) than that of dilute acids, due to the higher concentration of acid molecules.

Why is the pH of concentrated acids more dangerous than that of dilute acids?

The higher concentration of acid molecules in concentrated acids means that they are more corrosive and can cause more damage to living tissues.

Can the pH of a concentrated acid be lowered further?

Yes, the pH of a concentrated acid can be further lowered by adding more acid molecules, increasing its concentration.

How do you calculate the pH of a concentrated or dilute acid solution?

The pH of an acid solution can be calculated using the formula pH = -log[H+], where [H+] is the concentration of hydrogen ions in the solution. Concentrated acids will have a higher [H+] and therefore a lower pH compared to dilute acids.

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