Ocean Acidification, part one (Acids and Bases)

First, let's take a look at acids and bases. It's important to understand the ocean is not becoming acidic, even thought its pH is changing. "Acidic" sounds scary and it's not an accurate word.

A bit of molecular and atomic structure and chemistry are necessary to understand acids and bases. We'll start with water. Water is one atom of oxygen and two of hydrogen. Atoms consist of protons (with a positive charge +) and electrons (with a negative - ). This is how water's molecular structure can be drawn: 

If an atom (one element) or molecule (atoms combined) loses an electron, it becomes positive  (+).  Hydrogen missing one electron is called a hydrogen ion. These ions in water are what determine the pH. When water splits, you get:

The hydroxide ion has the hydrogen ion's

electron.

Now, these ions have unequal amounts of electrons and protons (The hydrogen ion has 1 proton, no electrons and the hydroxide ion has 7 protons and 8 electrons). 

How does this relate to acids and bases? A solution with extra H+ ions is called "acidic". One with OH- is called basic. Water--with no ions (the molecule remains H₂O) is considered

neutral.

The amount of H+ determines the pH. What is pH? In scientific jargon, pH=-log [H+], or the pH is equal to minus the log of the H+ ion concentration. (Wow! That made no sense at all!) If we look at a more simple explanation, the concentration of H+ determines the pH for acids. (Thank you, that's easier to understand.) pH goes from 0 (extremely acidic) to 14 (extremely basic/alkaline).

Let's look at some examples of pH.

pH 0 battery acid

pH 1 stomach acid

pH 2 coke, lemon juice, vinegar

pH 3 orange juice, grapefruit juice

pH 4 tomatoes, acid rain

pH 5 black coffee, pure rain

pH 6 egg yolks, cow's milk

pH 7 pure water

pH 8 sea water

pH 9 baking soda

pH 10 some hand soaps, some toothpaste

pH 11 ammonia

pH 12 household bleach, soapy water

pH 13 oven cleaner, lye

pH 14 liquid drain cleaner

As you can see, many common liquids have a pH much lower than sea water. Only when you get to stomach acid and battery acid do you see the "scary" side of acids, the ability to damage skin and inorganic materials. (Of course you can't really see stomach acid.) There are chemical acids that can harm you--ocean water is not and will not be one of them.

Also, it is very clear the ocean is not acidic. The pH is 8.3, which is higher than water. (pH can be kind of hard to picture--the lower the pH, the more acidic a solution is, the higher the pH, the more basic a solution is.)

If you mix an acid with a base in equal amounts, you get water and salt.

Concentration and strength of acids and bases are not the same thing. Strength refers to how much of the substance (CO₂, etc) are present in ionic form CO₂- versus the same substance in molecular form. Concentration is the amount of the dissolved substance in a specified amount of solvent. For example, hydrochloric acid (HCl) is a strong acid:
nearly all the Hydrogen separates from the Chlorine in water. There are various concentrations of HCl which can range from low to very high. A very high concentration would be quite corrosive. The concentration of carbonic acid in the ocean is around .3 to .4 %.

Carbonic acid is a weak acid. Most CO₂ just dissolves in water, remaining as CO₂ rather than becoming carbonic acid.

 

Acids and bases can be harmful due to strength, concentration and what they are made from. As we just learned, hydrochloric acid (HCl) is very strong—virtually all of the hydrogen and clorine separate in water.  

Concentration is the amount of the acid in the solution.  If you put 2 measures of hydrochloric acid powder in a quart of water, that is less concentrated than if you add 10 measures of powder in a quart of water. The concentration is dependent on the person mixing the solution.

Acids that form with chemicals like cyanide are harmful because of the cyanide molecule.  Cyanide is extremely toxic.

That's all for now on acids and bases.