Adding fish to the family leads tp pH discussion

April 09, 2004|by LISA TEDRICK PREJEAN

We went to a friend's 40th birthday party and brought home a fish.The door prize that my husband won was our introduction to life in The Deep. Now our 9-year-old can't read enough books on aquaculture, and he tells us to buy things like gravel vacuums and algae scrubbers.

"Goldie" is pretty cute, so we've made him a cozy home, complete with shells, plants and the all-important filter.

The other day as my son was reading about water chemistry in one of his fish books, he asked what pH is.

"It has something to do with acids and bases," I said while loading the dishwasher.

He seemed a little frustrated by my answer.

"The book tells me that, Mom. What I want to know is what pH stands for and why it is important."

The p in pH is from the German word Potenz, meaning "power" and the H is the chemical symbol for Hydrogen, Shari Palm, a fifth-grade teacher at Boonsboro Elementary School, explained via e-mail.


Palm and Rebecca Bland, a fifth-grade teacher at Bester Elementary, explored pH in a science task they wrote for county teachers.

Kimberly Jensen likes to help children remember that pH refers to the "power of Hydrogen."

The stronger the hydrogen ion concentration, the lower the pH. The weaker the hydrogen ion concentration, the higher the pH, explained Jensen, who is teaching Simple Chemistry at SonLight's Homeschool Spring Co-op.

Scientists use the pH scale to measure how acidic or basic a liquid is.

The scale goes from 0 to 14, with 0 being the most acidic, 7 being neutral and 14 being the most basic.

Acids typically taste sour, react with bases to produce salts and water, conduct electricity when dissolved in water and can burn skin and other tissues, Jensen explains.

Bases typically taste bitter and feel soapy or slick. Strong bases - such as oven cleaner - are harmful to skin and can destroy tissue. Bases also conduct electricity when dissolved in water.

The most striking property of both acids and bases is their ability to change the color of certain papers - called Litmus paper - or change the color of vegetable materials, according to Palm.

Earlier this week, Jensen guided a class through a red cabbage water experiment that both she and Palm recommend to help elementary-age students understand pH.

"It might look like we're coloring Easter eggs today, but we're not," Jensen joked with her class.

When red cabbage is soaked in water, the liquid turns purple. That liquid can be used as an indicator to test whether substances are acids or bases.

Jensen and her students added several common household items to small amounts of indicator (the purple liquid from the red cabbage).

Bases turned the liquid from purple to blue. Acids turned the liquid from purple to red. The color did not change when a neutral substance was added.

For example, a pinch of baking soda turned the cabbage juice blue. A few drops of vinegar turned the cabbage juice red. Rubbing alcohol, which is neutral, did not change the color.

To show how acids neutralize bases and vice versa, the opposite-type substance was added to neutralize it again - turn it back to its original color.

If you do this experiment in your kitchen, ask your child to guess which items are acids, which are neutral and which are bases.

"Make a guess before you do it," Jensen suggests. "Scientists make a guess first."

After grating the cabbage in her food processor, Jensen left it in water for about five minutes to make the indicator.

Palm says she teaches this lesson for the purpose of identifying chemical reactions. One way to identify a chemical change is by a change of color. When the indicator solution changes color, we know that there has been a chemical reaction.

Having children complete a chart is a good way to teach data collecting and organizing, an important scientific skill. Jensen says the chart can be as simple as a list of the substances to be tested down one side with three columns labeled "acid, base and neutral" at the top. The children simply place a mark under the proper column to identify each substance after testing with the cabbage indicator.

What does all this have to do with fish? Most fish like to have pH-balanced homes, somewhere close to neutral.

Lisa Tedrick Prejean writes a weekly column for The Herald-Mail's Family page. Send e-mail to her at

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