system
Given the following post, respond as if you're commenting on Reddit:
human
How can chemicals like CO2 acidify water if they don't contain H+?
gpt
Hello there,

Carbon Dioxide, when it dissolves in water and becomes what is known as an *aqeuous ion* in chemistry, essentially splits a water molecule thanks to its higher electronegativity in relation to the water molecule.

The new molecule that forms is known as *Carbonic Acid* with formula H2CO3.

The equilibrium equation looks like this :

CO2 + H20 <==> H2CO3^- + H^+

Carbonic acid is a very weak acid, with a equilibrium pH of 5.7 at one atmosphere of pressure at room temperature.

Carbonic acid also rapidly decomposes, given time, into CO2 gas and water. Its acidic equilibrium is maintained by keeping solutions at pressures only slightly higher than 1 atmosphere.

The very best examples of carbonic acid in every day life are :

* A can of carbonated soft drink.
* Respiration

In a can of carbonated soft drink, the fizzyness of the liquid comes from being a solution of carbonic acid, kept in equilibrium by being canned at a pressure greater than 1 atmosphere. When we open the can, the pressure of the can is brought into a new equilibrium with the outer atmosphere, at 1 atm. As a result, the CO2 dissolved in the water now starts to escape, and the drink is saturated with bubbles of escaping gas - which is very pleasant on the tongue of the person drinking it. Eventually, all the gas escapes out of the water, and we say that the drink is 'flat', and contains no escaping gas.

In our blood, and in the blood of all other animals, cellular respiration produces CO2 as a waste gas by product of glycolysis and other metabolic energy processes. To keep this from poisoning the cells, large animals (like us) dissolve this CO2 into the blood in the form of Carbonic Acid, H2CO3. The solution is very dilute (blood does not, after all, fizz when we get a small cut of a vein), but the solubility of CO2 in water as Carbonic acid is good enough to allow the gas to escape into the alveoli of the lungs, and then be exhaled into the air in the process of respiration.

The small amounts of CO2 from soft drinks and human&animal respiration are taken up by plants in the sea and the land, to make new plants, food, and biological material for the animals - this is the biological carbon cycle.

As rain drops fall through the air, they have enough time to interact with CO2 in the upper troposphere to form weak carbonic acid solutions. In areas of extreme CO2 concentration in the air (though this is typically a little over the mean atmospheric CO2 concentration 0.25% on average), the result is what is known as *Acid Rain*, which in turn can have effects on lakes and rivers, but only over a very short time.

By the way, this naturally occurring acid rain is not related to the more desctructive Acid Rains created by human industrial pollution of the atmosphere by sulphur chemistry, where rain combines with Sulphates in the atmosphere to form the very corrosive Sulphonic Acid, a close a relative of the very corrosive Sulphuric Acid. Acid rains, in general, are not very destructive unless sustained over incredibly long periods of geological time.

Hope this helps.