Phun with pH

By:

 

Can playing with pH be phun? It is when you learn about it from brilliant Nasa Project Scientist, Dr. Steven Howell.

 

Dr. Steve was kind enough to lend his expert knowledge to IACP Kids special project with the School Without Walls at Francis Stevens in Washington, DC.

 

We found that knowing the pH of something you care about--from culinary ingredients to the soil that nourishes our food--can make all the difference. Best of all, we got to see the results in a galaxy of wild colors!

 

 

Our first question was a pretty basic one: What exactly is pH?

 

Dr. Steve said that pH is a scientific measure of the acidity or basicity (alkalinity) of an aqueous solution. The scale used to measure pH runs from a value of 0 (the most acidic stuff we know) to a value of 14 (the most alkaline stuff we know).

 

 

pH is critical for everyone. Life is actually dependent on the pH of your blood. Human blood is slightly basic, with values ranging from 7.3 to 7.5. If the pH drops below 7.0 or rises above 7.8, the body can't survive.

 

All solutions, including the foods we eat, the fertilizer for our yards, and the products that you use to clean your house, have a pH. They can be either acidic, neutral or basic. If you know the the pH of these solutions, you can learn a lot -- and avoid harmful reactions/.

 

Scientists measure pH using the same kind of "log scale" that's used to measure the strength of an earthquake.

A log scale means that a solution with a pH of 4 is ten times more acidic than a solution with a pH of 5 and a solution with a pH of 12 would be ten times more basic than one with a pH of 11.

Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. For example, distilled water has a neutral pH of 7, lemon juice has a pH of 2.2 (acid), and ammonia has a pH near 11 (base).

 

 

We learned that pH means "power of hydrogen." The concept of pH was first introduced by Danish chemist Soren Sorensen at the Carlsberg Laboratory in 1909 and was revised to the modern pH scale in 1924. The lower case p stands for "power" and chemically, pH = concentration of hydronium ions (H±).

 

Pretty technical, huh? We thought so, too!

All this expert knowledge was making us feel pretty powerful. We wanted to learn how we could measure pH using ingredients we could find at home.

 

Recreating the same sort of experiment scientists perform in their labs turns out to be fun and easy--and you can do it in your own kitchen!

Over the years, chemists have learned that certain substances change color when they're exposed to an acid or a base. Dr. Steve showed us how to test pH using a red cabbage solution and pH test strips.

 

 

If you'd like to try it yourself, here's what we did:

 

Phun with pH Experiment

 

WHAT YOU NEED

 

For your indicator solution:

 

A big pot (4-6-qt. capacity)

 

Red cabbage (about 2 cups if you're doing the experiment on your own—1 small red cabbage for a group)

 

Enough water to cover the cabbage

 

For test strips:

 

pH Test Strips (available at most pharmacies)

 

Ingredients to test:

 

Plain water

White vinegar

Lemon juice

Soy sauce

Coke or Pepsi

Baking soda

Salt

Sugar

Eggshells

 

WHAT YOU DO

 

 

NOTE: You'll need an adult's help with using a knife to cut the cabbage, cooking the cabbage pieces and draining the cabbage water. If there's any other part of the experiment you feel unsure about, always ask for an adult's help!

 

PREPARE YOUR SOLUTION

 

Cut the cabbage into small pieces, then place it in a stainless-steel pot.

 

Pour in water to barely cover the cabbage.

 

Boil the water until the cabbage is tender (about ten minutes).

 

Let the water and cabbage cool, then carefully drain the cabbage water through a strainer into a heatproof bowl or beaker.

 

Carefully pour the cabbage water into small jars (one for each ingredient you want to test).

 

If you like, save the cabbage to eat with a vinaigrette, a pinch of sugar and some chopped apple.

 

 

TEST YOUR INGREDIENTS

 

To test the pH of your ingredients, mix a pinch or splash into a jar of cabbage solution.

 

When you mix in a base (like baking soda), the purple solution should turn greenish.

 

When you mix in some acid (like vinegar), the purple solution should turn blue.

 

To find the exact pH, use one of the test strips.

 

As you add more ingredients, the color of your solution will change—and so will the pH.

 

Have fun with your experiment!