# Comparing the pH of H2CO3 and H2SO4 Solutions

• Orion78

#### Orion78

Pollution from fireworks occurs in a number of ways, one of which is the release of gases such as carbon dioxide (CO2) and sulfur dioxide (SO2) into the environment. These gases react further in the atmosphere to produce carbonic acid (H2CO3), a weak acid, and sulfuric acid (H2SO4) a strong acid. If the same number of moles of each of these acids were dissolved in equal volumes of water, how can I state and explain which of the resulting solutions would have the higher pH. Has this to do with the fact in weak acids the equilibrium lies well over to the left-hand side of the equation? But what does it means?
Furthermore, which changes take place when each compound is dissolved in water? What are the two equations? Is the equilibrium state dynamic?

This is what I was thinking but I feel like something is missing:

The acid concentration of both compounds dissolved in water is the same, but sulfuric acid will have a higher pH and is therefore a stronger acid than carbonic acid. This is because the concentration of the ions for carbonic acid is lower compared with that of the sulfuric acid, which dissolves in water better. In the dissociation of sulfuric acid, more molecules dissociate into hydrogen ions than in the carbonic acid. In both acids the concentration of hydrogen ions exceeds the concentration of hydroxide ions, but in sulfuric acid is greater than in carbonic acid. When each compound is dissolved in water, their molecules are separated from one another and they change their original state into aqueous. Their equilibrium state is dynamic, in fact for both acids molecules are continuously breaking down into Bicarbonate/Sulfate ions and Hydronium ions and this is balanced by the reverse reaction where Bicarbonate/Sulfate ions and Hydronium ions recombining to give acetic and carbonic acid molecules.

H2CO3 (aq) + H2O (l) ⇌ H3O+ (aq) + HCO3− (aq)
H2SO4 (aq) + H2O (l) ⇌ H3O+ (aq) + HSO4− (aq)

Thanks!

Orion78 said:
sulfuric acid will have a higher pH and is therefore a stronger acid

First, pH will be lower, not higher.

Second, it the other way around - sulfuric acid is stronger, therefore its solution has a lower pH.

You wrote a lot, mostly of what you wrote is true, but irrelevant. Stronger acids dissociate more easily, so their solutions (assuming identical concentration) have lower pH. That's all that is needed here.

Thank you Borek for your corrections. But HOW, taking in consideration my two solutions, I can state which of the resulting solutions would have the higher pH? Can I might see it from their equations? What does it means that in weak acids the equilibrium lies well over to the left-hand side of their equation? Furthermore, which changes take place when each compound is dissolved in water? It is correct what I wrote about their equilibrium state?
Thanks.

Orion78 said:
But HOW

Depends on the level of your education. On the lowest level you can describe it only qualitatively, stronger acid dissociates more producing lower pH. On the more advanced level it can be shown by calculating exact pH using concentrations and dissociation constants.

Not that the results will be different.