Skip to content

1

Thinking of the lovely spring colors, the pastel blues, lavenders, yellows and pinks? Why not try a few really fun experiments creating and changing colors using chemistry?

The first experiment requires some fresh red, blue or purple flowers (purple petunias work really well); a jar big enough to hold a few flowers with a lid; some twist ties, string or yarn to suspend the flowers; household ammonia; and for the optional last part, vinegar (any kind). The ammonia is pretty strong, so this will require help from an adult.

Have an adult pour about 1/2-inch ammonia into the bottom of the jar. Wrap a twist tie or yarn around the stems of the flowers, enough that will fit comfortably into the jar. Suspend the flowers upside-down into the jar so that they are close to, but not touching the ammonia, by wrapping the yarn or twist tie over the lip of the jar. Put the lid on the jar as much as you can. Wait about 15 minutes and you should see the flowers start to change color.

This part of the experiment is based on one by Robert Krampf in his excellent Experiment of the Week series, although I couldn't find it in his archives. Edit: Robert Krampf has revamped his site, and so this link is no longer valid. Check out the fun stuff he has to offer at the Happy Scientist.

Now comes my addition: once the flowers have changed color nicely in the ammonia (which is a base) then try to change the color back by dipping the flowers in a bowl of vinegar (an acid). Using purple petunias, I was able to turn them a bright teal blue in the ammonia, and then back to purple in the vinegar. You can actually dip them into the vinegar, because it won't bleach. It you dip the flowers into the ammonia, however, it may bleach or discolor them. That is why they need to be suspended in the fumes instead.

The second experiment is the classic use of red cabbage as a pH indicator. If you haven't done this, it really is fun. All you need is red cabbage from the grocery store, a blender (ask for an adult's help), glasses or plastic cups and items to mix with the red cabbage solution, such as lemon juice, soda, vinegar, baking soda, dish detergent and laundry detergent.

Some recipes call for boiling the cabbage (smelly!), but I just ground up the fresh red cabbage in small batches with just enough water to allow the blender to work properly. Pour the batches together in a pitcher (which can be placed in the refrigerator for use later in the day if necessary.) Pour about 1/3 cup of the red cabbage juice into testing containers such as clear glasses or plastic cups. Then mix in about a Tablespoon of one of the testing compounds. Does the color change? Try another material in the next glass. Does the color change more if you add more test material? What happens if you mix two materials, like vinegar and laundry detergent? Have fun admiring the wild colors you can make.

What is happening? The pigment molecules in the red cabbage change shape, and thus color, when in the presence of acids versus bases. Lemon juice, vinegar and soda are acids; detergents and soaps are bases.

For the grand finale, create more wild colors with markers. Fold up a diaper wipe that contains alcohol and tie in bunches with rubber bands. Color with Sharpie-type markers. Allow it to set a few minutes and then unfold to reveal a rainbow of colors in a cool tie-dye pattern. Experiment with more wipes to see what you can create. Note: allow to dry suspended on a line so the dye doesn't move onto other surfaces.

If you don't have diaper wipes, then try white fabric. Tie with rubber bands, if desired and then color with markers. Drop or dribble on some rubbing alcohol and the colors should separate and move through the fabric. Once again, keep on a line or suspended until dry. Once you have the technique refined, you might want to create your own tie-dye T-shirts or socks.

Spring colors rock!

Spring is in the air. What a wonderful opportunity to get outside and go for a walk. Do you have a favorite trail or park to visit? What about the local nature center, arboretum or botanical garden? Take a few minutes from your hectic schedule and go on a stroll.

While you are outside, take a look around at the spring flowers. In some areas you may see the pussy willows just starting to bud and snowdrops peaking through melting snow. In other areas, the poppies may be starting to wane as the heat builds up. Wherever you may be, stop and enjoy the color and beauty of flowers.

You might be wondering what a nature hike has to do with science, even though it is certainly fun. It turns out you can do science while on a nature hike and it won't even be hard.

Take a closer look at the flowers you find. Notice if you can smell anything. Are the flowers all one color or are they a mix of colors within a single flower, like the darker orange patches in the yellow flower below? Are there any insects around? Observing is an important science skill, which is simple to do and can lead to further explorations. Do you find the plants in a certain place, such as out in the open or hidden under some brush? Do the plants change over the season? All of these observations can lead to further questions and even to experiments.

Do you know what kind of plants you are finding? Classifying is another important science skill, but it doesn't necessarily mean you have to learn the scientific name of everything you see. Classifying can simply mean grouping things based on similarities and differences. For example, you can group all the flowers you see based on the their color, leaf shape or size. Is the flower you are seeing now is the same as the one you just saw over there, or is it different? With children, start a conversation about how they would name the flowers. You can also ask how they would find out the name others have given the flowers.

When you get home, you might want to look up the common and/or scientific names of one or two of the flowers. There are many excellent books or you can use Internet sites like this one from Texas. In any case, hope you have an enjoyable weekend.

nasturtium

The Science of Making Cheese

Little Miss Muffet
Sat on a tuffet,
Eating her curds and whey;
There came a big spider,
Who sat down beside her
And frightened Miss Muffet away.
~ Mother Goose

What are "curds and whey?" Where does cheese come from? Let's make some homemade cheeses and find out!

The easiest cheeses to make are the so-called soft cheeses like cottage and ricotta cheeses. To make a soft cheese, simply add an acidic substance like lemon juice or vinegar to warmed milk. The proteins in the milk clump or coagulate together forming the curds. The curds are then separated from the remaining cloudy, yellowish liquid, which is called the whey. When making cheese at home, the whey is discarded. When cheese is made commercially, the whey is often collected and added to baked goods and other foods.

In contrast, making hard cheeses, such as cheddar, is more complicated and requires more time. Usually, instead of the lemon juice or vinegar, an enzyme called rennin is used to coagulate the milk proteins. Once the curds are formed, they are ripened by the addition of special molds or bacteria to create distinctive flavors. The mold can actually be seen in blue cheese, it gives the cheese its blue color. During or after ripening, the curds are pressed to create blocks or bricks.

Following are recipes for two soft cheeses. One is made from cows' milk, the other from soymilk.

Cottage Cheese
Note: This project will require adult assistance and supervision. Hot, thick liquids like milk can boil over quickly and unexpectedly.

Utensils:
A colander or strainer
A large bowl
Cheesecloth (white cotton cloth for food use, available at many grocery stores, or use clean paper towels if no cheesecloth is available.)
Saucepan
Long-handled spoon
Stove

Ingredients:
2 cups of cows' milk, any kind
3 Tablespoons of lemon juice or vinegar
Directions:
1. Place the colander over the bowl (or in if the bowl is big enough). Line the colander by draping layers of cheesecloth (or paper towel) over the sides.
2. Pour the milk into the saucepan. Add the lemon juice or vinegar. Place the saucepan over low heat and stir slowly until the milk curdles (forms soft lumps and clumps). This usually takes about five minutes. Remove the saucepan from the heat. Let stand for ten minutes to let the curds (clumps) and whey (liquid) form and separate somewhat.
3. Pour the curdled milk into the cheesecloth. Allow the whey to drip through. Catch the solid part, the curds. Once most of the liquid seems to have moved through the cheesecloth, pull the edges of the cheesecloth over the curds and press gently to remove as much of the whey as possible. Once the curds are approximately the consistency of commercial cottage cheese, which should be in 15-20 minutes, they are ready to eat. Transfer to a clean container, cover and refrigerate if not used immediately.

Are you allergic to dairy products? Here is a dairy-free cheese.
Soy Ricotta Cheese
Note: This project will require adult assistance and supervision. Hot, thick liquids like soymilk can boil over quickly and unexpectedly.
Utensils:
A colander or strainer
A large bowl
Cheesecloth (white cotton cloth for food use, available at many grocery stores)
Sturdy, heavy-bottomed saucepan, or double boiler if available
Long-handled spoon
Stove

Ingredients:
1 Quart unsweetened, unflavored soymilk (or smoothly blend 1 cup soy flour in 1 quart of water)
3 Tablespoons of lemon juice or vinegar
Directions:
1. Place the colander over or in the bowl. Line the colander by draping layers of cheesecloth over the sides.
2. Pour the soymilk into the heavy-bottomed saucepan or top of the double-boiler. Place the saucepan over low heat and stir constantly until the soymilk boils. Watch closely and stir frequently, because the soymilk burns easily. If the soymilk begins to burn (brown or blacken at the bottom of the pan) quickly transfer to another pan and continue stirring. Transferring will lessen the chances of a burnt flavor.
3. Remove the saucepan from the heat. Add the lemon juice or vinegar and stir. Let stand for twenty minutes to let the curds (clumps) and whey (liquid) form and separate somewhat.
4. Pour the curdled milk into the cheesecloth. Allow the whey, or watery part to drip through. Catch the solid part, the curds. Once the liquid seems to have moved through the cheesecloth, pull the edges of the cheesecloth over the curd and press gently to remove as much of the whey as possible. Once the curds are the consistency of cottage cheese, they are ready to eat. Optional: add salt, diced tomatoes or herbs.

These soft cheeses work well in lasagna or in enchiladas, too.