Monday, February 10, 2014

Let’s Talk Science: A pH Solution

By Brook Beeler, Communication Manager, Eastern Region

We are all familiar with the term acid and we often hear about the pH scale, but what does it really mean? What is the pH scale really all about?

It is a delicate dance at the molecular level. Let’s break it down.

The foundational parts

Water molecule
Water molecules are made up of
one oxygen atom and two hydrogens.
Distilled water has a neutral pH of 7.

Molecules are made of atoms and are generally considered neutral, meaning they do not have a positive or negative electrical charge. Water is an example of a neutral molecule made of one oxygen and two hydrogen atoms. A neutral molecule is considered stable and happy.

In the molecular world, though, being happy isn’t always good enough. Molecules are often in a state of flux. The atoms that make up molecules tend to move around a lot. Molecules may break apart to form ions, which do have a positive or negative electrical charge. Ions can be an atom or multiple atoms combined. If our water molecule breaks apart, the likely combinations of ions would be positively charged hydrogen and oxygen bonded to hydrogen or hydroxide, resulting in a negative charge.

Acid and base

The pH scale helps scientists measure whether or not a solution is acidic or basic. In chemistry, a solution is defined by one substance being dissolved in another. Solutions are easiest to understand as a liquid, but it is important to note that they also exist in gas and solid forms.

An acid is a solution that has a higher concentration of positively charged hydrogen ions (H) than negatively charged hydroxide ions (OH). Common examples of acids are lemon juice and vinegar. A base has a higher concentration of OH ions. Common examples are baking soda and household ammonia.
The scale ranges from 0 to 14. Smack dab in the middle (7) is considered neutral, which is neither acidic nor basic. And what substance do you suppose comes in at that number? Our happy water molecule. When water is in a pure or distilled state, it measures a pH of 7. The lower the number (0-7), the more acidic it’s considered. And the higher the number (7 to 14), the more basic it is.

The pH scale may seem small, but each whole number represents a ten-fold leap in concentration of either H ions or OH ions. For example, rain is slightly acidic with a pH that measures about six. A grapefruit is approximately three on the pH scale. That means that a grapefruit is 1,000 times more acidic than rain.

Both acids and bases play important roles. They help us clean and, in some cases, make delicious salad dressings. However, an overabundance of solutions that are too high or too low on the pH scale can cause problems with our health and the environment.

Our work related to pH

pH affects people and the environment and can be toxic. At very high or very low pH levels, those charged ions dancing around in solutions want to find a mate of the opposite charge. They woo neutral molecules, attracting them away from stability. For example, metals like aluminum become soluble at a low pH. This means it is more likely to dissolve and move through a solution and make its way into drinking water or the food chain. That’s no good.

In bodies of water, pH is generally very stable and the value doesn’t change much. However, if we notice that pH values change, it’s likely an indication that some sort of pollution is affecting the water.

So we pay attention to pH. We require wastewater discharges and air permits to address pH. It is a parameter often addressed in our water quality improvement plans. It can also indicate if a waste material is dangerous and has specific disposal requirements according to state laws.

Holcim Inc. Toxics Cleanup Site’s problem is with pH. Holcim owns property along the Spokane River in Spokane Valley where soil and groundwater is contaminated with cement kiln dust.

Holcim and its predecessor companies operated a cement manufacturing plant at the site until 1967. Cement kiln dust, a byproduct of cement manufacturing, was landfilled on the northern portion of the site before Washington state laws for dangerous waste prevented that practice.

Cement kiln dust has a high pH and is considered caustic. Because we pay attention to pH and the complex nature of groundwater, proximity to the river and location of drinking water wells, Ecology required the parties responsible to investigate the contamination and evaluate cleanup options.

This cleanup site is in early stages of the cleanup process. But Ecology is continuing to work with the property owner to give this site a clean bill of health. A cleanup option will be selected and implemented ensuring that there is a pH solution for the health of people and the environment.

For current information visit the Holcim Inc. cleanup site webpage.

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