Hands-on Science         (Laurel F. Appel)

 

Never-Fail Experiments we have done in schools, scout troops, and libraries, with grocery-store ingredients and kitchen tools.

 

Courtesy of:

Wesleyan University Women in Science,

the Wesleyan Hughes Program, and

The Science Moms

 

Remember the basic rules for science experiments:

 

Red Cabbage pH indicator.   (for testing for acids and bases in your kitchen)

            Get some red cabbage from the grocery store, chop it into fairly small pieces, put in a microwave-safe bowl, cover with water, and microwave for a few minutes.  The exact time will vary with amount.  Boil it gently, until the water is fairly dark purple.  If you boil it too long, the pigment will break down and you'll lose color.  Let it cool, pour the liquid off of the cooked cabbage, and use the liquid to test the pH of different things.  Lemon juice, baking soda, vinegar, soda pop, Tums, and laundry detergent are a good start.  Put a spoonful of the purple juice into a white cup (or test tube, if you have one) and add a few drops of whatever you want to test. Acids like vinegar or orange juice will turn the indicator pink. (The acidity is what makes it sting if you get orange juice on a cut in your mouth.)  See what color laundry detergent turns the indicator: probably not what you would guess! 

 

Home-made Silly Putty                (polymer chemistry)

2 Tablespoons of white glue (Elmer's)

2 Tablespoons of water

a drop or two of food coloring

2 teaspoons of borax  (we use 20 Mule Team from the laundry detergent aisle.  Note: this is poisonous.)

Put the white glue and water in a bowl (we use disposable plastic bowls) and stir to mix. Add some drops of food coloring, and stir again. Add the borax last.  It will start to congeal immediately, as the borax cuases crosslinkinng between the strands of glue polymers.  Stir, then transfer to a ziplock bag. That way, you can knead it without getting your hands covered with food coloring.  Knead thoroughly, until it makes a smooth blob.  Any residual graininess or wetness can be rinsed off with water in the sink. Now play with it.

Store it in the ziplock bag when not using it, so it doesnıt dry out.

 

Racing Ink Spots    (paper chromatography separation of chemical mixture)

            Cut a strip about 1 inch by 4-5 inches from coffee filter, and pencil a line 3/4 inch from one end.  Put dots of different washable black ink in a row on the line.  Then suspend the strip above a cup of water, so that the strip dips into the water, but the spots are NOT in the water.  (Put a straw or pencil across the top of the cup, and use a clip to hold the paper to it.) As the water is sucked up into the dry filter, it will drag the spot of ink up with it.  If the ink is a mixture of colors (which all washable black inks are) the different components will move at different speeds, depending on whether they stick better to the paper or the water.

Chemists use this technique, in various forms, to separate all sorts of molecules from each other.

 

Isolating DNA, the information molecule of life

  - Yes, you can do this at home!

 

DNA is the molecule that contains our hereditary information: the instruction book for a kid, or a fly, or a flower, or an elephant.  It is all written in the same language, but with slight differences in recipes.  (Notice that elephants do not fly, and are not green.)

 

In this experiment, you will extract the DNA from wheat germ.  Because the DNA molecule is very, very long, to carry all that information, you can extract it as long, stringy, gooey threads.  Because there are so many molecules together, you will be able to see it, even though each individual thread would be too skinny to see.

 

What you need:

 

Materials

very warm water

. . .not hotter than 60 C, better too cool than too hot.

raw wheat germ

. . . or grated onion, or mashed banana, or other thing you think contains DNA.

MUST BE UNCOOKED.

liquid detergent

. . . shampoo or hand dishwashing detergent, preferably clear or

white.

 

rubbing alcohol, pre-chilled

from the drugstore, isopropyl alcohol or ethyl alcohol.  70% will do, 91 % is even better.  Stick it in the freezer or on ice to chill.

baking soda

. . . also known as sodium bicarbonate.

meat tenderizer

(or enzymatic contact lens cleaner)

 

. . . from the spice section, or substitute salt if you have none. We keep it around for bee stings.

 

Equipment

2 plastic cups

measuring cup

measuring spoons

spoon, plastic knife, or rod to stir

small strainer

funnel

test tube (or tall, narrow jar, such as for spices)

toothpick or bent paperclip (straighten, then make small hook at end)

 

Instructions.

 

In groups of 3 or 4,

1.              Measure 100 mls (1/2 cup) of very warm water (from the tap, but not hot enough to burn your hand: about 50-60 C) into a plastic cup.

2.              Add 1/2 tablespoon of raw wheat germ to the cup, and stir well.

3.              Add 1/2 teaspoon of detergent, and stir for one minute.    

The solution will get thick, as the detergent breaks apart the cell membranes, and releases DNA, as well as proteins and other components.

4.              Add 1/4 teaspoon of meat tenderizer, and 1/2 teaspoon of baking soda.

The meat tenderizer contains salt, which keeps the DNA intact, and an enzyme that chews up the proteins that keep DNA coiled up.  The baking soda is a buffer, which keeps the solution from being too acidic.

5.              Stir slowly for 1 minute, then let the solution settle and cool for a few minutes.

6.              Pour the top half of the liquid through a strainer and funnel into a new cup.

7.              Pour a little of this thick solution from the new cup into test tubes ­ one for each member of your group.  Fill each test tube only about 1/3 to 1/2 way.

8.              Gently add ice-cold alcohol (this is poisonous!) to each tube, and let it sit for several minutes.  Try not to mix the two layers. 

The DNA is dissolved in the water-based gooey bottom layer, but cannot stay dissolved in the upper alcohol layer.  You will see bubbles form at the interface between the two layers, and then the threads of DNA.

9.              Use a toothpick or bent paperclip to collect the DNA.  Hold it so the tip or hook is just below the bottom of the alcohol layer.  Turn it in ten very slow circles.  You should see threads or globs attaching.  Keep turning as long as you see more threads, then pull it out and admire your DNA.  You can save it in a capped tube of fresh alcohol, if youıd like.

The slimy glob of DNA you have wrapped around your paperclip is millions of strands that tangled together as you turned.  You can touch it.

10.           Clean up.  Do NOT send too much wheat germ down a drain, or it will clog.  Pour liquids into the liquid waste collection, collect wheat germ sludge into a plastic cup to put in the trash, and put all your equipment into a bucket to be washed.  Do you think you will need to add much soap to wash it?

 

DNA protocol adapted from http://gslc.genetics.utah.edu/units/activities/extraction/ and various other teaching  websites.

For more kid science, see my list at http://lappel.web.wesleyan.edu/k-12links.htm

Copyright 2004 Laurel F. Appel