Plants are wonderful chemical reorganizers. Using the sun’s energy and a process called photosynthesis, they can turn water and carbon dioxide into sugar (glucose) and oxygen.
Thanks to plants and other autotrophs like algae, Earth has an oxygen-containing atmosphere that can sustain animal and human life.
To watch plants make oxygen, all you need is a water plant like Elodea (available at pet stores), a large container, water and a few small clear glasses or test tubes.
Fill the large container with water and turn your small, clear containers on their sides underwater to remove all the air bubbles.
Cut a branch off of your plant, place it under water in the large container, shake off any air and put it under your small, clear container- stem side up. Invert the small container, allowing no air to enter it. Repeat the experiment with your other small clear container, but don’t add a plant. This is your control. If you’re using test tubes, you can put them in small cups or beakers so they don’t tip over. (See photo above.)
Place your experiment in bright sunlight or near a strong lamp and observe what happens. You should see oxygen bubbles form on the plant as it performs photosynthesis. In a test tube, you will eventually see some water displaced by oxygen.
What happens if you duplicate the experiment in a room with no light?
Tap water contains some carbon dioxide. How do you think the experiment would work with lake or pond water?
Here’s the video we made last weekend for KidScience app that shows you how to stand on a carton of raw eggs without breaking them:
Remember, Force is pressure per unit of area. In the video, you’ll see what happens when you try to stand on eggs in high heels and the force isn’t evenly distributed.
One of the first things you learn when you do science is that experiments don’t always turn out the way you hope they will. And that’s OK. If at first you don’t succeed….
We tried to measure how far a sneeze would throw visible droplets by putting grape juice in our mouths and tickling our noses with feathers dipped in pepper. Sadly, no matter how hard we tried, we couldn’t seem to sneeze with grape juice in our mouths. Laughing so hard we spit the juice out was one unexpected outcome. We decided to try it again in the future using petri dishes spaced at intervals to avoid the grape juice problem.
Since there was no school today and it was ten degrees below zero (F), we tried throwing boiling water into the air to see if it would freeze before it hit the ground. Once again, our experimental conditions were less than perfect, and although some of the water froze into an icy cloud, the majority hit the ground with a splash. The experiment would have worked better at -20F, but it was still fun!
Salt lowers the melting/freezing temperature of ice, which is the solid form of water. Here’s a fun experiment you can do to see for yourself how Sodium Chloride (table salt) makes ice melt and water refreeze on a string, allowing you to “magically” lift an ice cube from a glass of water.
Click here for detailed instructions and more about the science.
This video will soon appear on KidScience app‘s Premium version, which allows you to easily search for experiments and videos based on kids’ ages, type of science, what you have on hand, or how much time you have.
Ever wonder how much starch is in your Thanksgiving dinner? Click here for a fun experiment that lets you test your favorite foods for starch using iodine from the medicine cabinet.
Remember to supervise small children if you do this experiment, since iodine should not be ingested! Happy Thanksgiving!
It’s not quite hot enough to fry an egg on the sidewalk, but a hot summer day like today would be perfect for making a solar oven from a pizza box! (This is a repost of one of our summer favorites.)
When my friend Sheila, who works at NREL (the National Renewable Energy Laboratory) sent me this project, I couldn’t wait to try it out. We first tried it out on a cool spring day in Minnesota and to my surprise, it worked. The oven didn’t get very hot, but we were able to warm a chocolate chip cookie enough to make it soft and melt the chips.
NREL suggests using your oven to make s’mores, which we’ve tried and is really fun. (We did it on Kare11 last summer.) The solar oven is surprisingly easy to make. It only took us 10 or 15 minutes..
You will need: 1 pizza box from a local pizza delivery store (Little Caesars, Domino’s, Pizza Hut, etc.), newspapers, tape, scissors, black construction paper, clear plastic wrap, aluminum foil and a dowel or stick to prop the lid up. You will also want to have some food to warm in your oven-marshmallows, chocolate, etc.
Make sure the cardboard is folded into its box shape. Carefully cut out 3 sides of a square in the lid of the box. Do not cut out the fourth side of the square, which is the one closest to where the pizza box lid hinges. Gently fold the flap back along the uncut edge to form a crease. See photo below!
Now, Wrap the underside (inside) face of the flap that you made with aluminum foil. Tape it so that the foil is help firmly but so that there’s not too much tape showing on the foil side of the flap.
Open the box and place a piece of black construction paper so that it fits the bottom of the box. Tape it by the edges. (We used two pieces.)
Roll up some newspaper and fit it around the inside edges of the box. This is the insulation. It should be about 1-1 ½” thick. Use tape (or other materials you can think of) to hold the newspaper in place. Tape it to the bottom of the box so that you can close the lid. (We taped it to the sides and had to cut the tape so that we could close the lid. Luckily our newspaper fit in tightly enough that we didn’t really even need the tape.)
Finally, cut plastic wrap an inch larger than the lid opening on the box top. Tape it on the underside of the lid opening. Add another piece of plastic wrap to the top of the lid opening. This creates a layer of air as insulation that keeps heat in the box. It also makes a window you can look through at the food you’re “cooking.” BE SURE THE PLASTIC WRAP IS TIGHT.
You are almost done! According to NREL, the oven needs to sit at an angle facing the sun directly so you’ll need to make a prop. You could probably just use a book or something under the hinged side of the oven. However, I missed this when I read the directions and we just put it flat on the ground. The flap of the box top needs to be propped open—a dowel or ruler works great. We used a wooden skewer that I broke the sharp point off of. This way you can change the amount of sunlight striking the oven window. Play with the angle of the flap to see how much sunlight you can get to reflect on the food.
Check every once in a while to see how well your food is being heated by solar thermal energy. If you’re is interested in finding out how the sun cooked your food, go to http://www.nrel.gov/ NREL’s website has great information on solar energy and many other sources of renewable energy.
Would you be surprised if I told you that you could stand on a carton of raw eggs barefoot without breaking them? Or that you can squeeze an egg with all your might without even cracking it (provided there are no cracks in the egg and you’re not wearing a ring?)Here’s a video of us doing these eggsperiments on Kare 11 Sunrise news!
Chicken eggs have delicate enough shells that chicks can peck their way out, but their architecture is nothing short of amazing. Their arched shape makes them able to handle large amounts of pressure without cracking, which is extremely important, since hens must sit on them in order to hatch them out. Humans use arches too, for designing strong building and bridges.
Remove any rings you’re wearing, place a raw egg in a plastic baggie and wrap your hand around it evenly. Squeeze as hard as you can. Did you break it?
Remove your socks and hold on to a chair or someone’s hand. Carefully step onto the eggs with your entire foot. Remember: pressure is force per unit of area. The idea is to equally distribute your weight, and therefore the pressure, across all twelve eggs. Let go of the chair.
Did it work? How important do you think it is to keep your foot flat? What would happen if you tried the same experiment in pointy high-heels?
Remember to wash your hands after touching raw eggs so you don’t spread Salmonella bacteria around!
Diffusion is the name for the way molecules move from areas of high concentration, where there are lots of other similar molecules, to areas of low concentration, where there are fewer similar molecules. When the molecules are evenly spread throughout the space, it is called equilibrium. Imagine half a box filled with yellow balls and the other half filled with blue ones. If you set the box on something that vibrates, the balls will start to move around randomly, until the blue and yellow balls are evenly mixed up.
Think about the way pollutants move from one place to another through air, water and even soil. Or consider how bacteria are able to take up the substances they need to thrive. Your body has to transfer oxygen, carbon dioxide and water by processes involving diffusion as well.
Lots of things can affect how fast molecules diffuse, including temperature. When molecules are heated up, they vibrate faster and move around faster, which helps them achieve equilibrium more quickly than they would if it were cold.
Diffusion takes place in gases (like air), liquids (like food coloring moving through water,) and even solids (semiconductors for computers are made by diffusing elements into one another.)
You can watch food coloring diffuse through a colloid (gelatin) at home and measure how long it takes. Gelatin is a good substance to use for diffusion experiments since it doesn’t support convection, which is another kind of movement in fluids. You’ll need clear gelatin (from the grocery store or Target), food coloring and water.
Add 4 packs of plain, unflavored gelatin (1 oz or 28 gm) to 4 cups of boiling water. Pour the liquid gelatin into petri dishes, cups, or tupperware and let it harden. Then, using a straw, poke a hole or two in the gelatin, removing the plug so that you have a hole in the jello about 1/2 inch deep. Add a drop of food coloring in the hole in the jello.
Every so often, measure the circle of food coloring as it diffuses into the jello around it. How many cm per hour is it diffusing? If you put one plate in the refrigerator and an identical one at room temperature, do they diffuse at the same rate? Why do you think you see more than one color for certain shades of food coloring? What else could you try?
Here’s a post on how to use this experiment to make sticky window decorations: http://kitchenpantryscientist.com/?p=4489
We made plates and did the same experiment using 2 cups of red cabbage juice, 2 cups of water and 4 packs of gelatin to see how fast a few drops of vinegar or baking soda solution would diffuse (a pigment in red cabbage turns pink when exposed to acid, and blue/green when exposed to a base!)
It’s also fun to experiment with the diffusion of substances across a membrane, like a paper towel. This is called osmosis. Membranes like the ones around your cells are selectively permeable and let water and oxygen in and out, but keep other, larger molecules from freely entering and exiting your cells.
For this experiment, you’ll need a jar (or two), paper towels, rubber bands and food coloring. Fill a jar with water and secure a paper towel in the jar’s mouth (with a rubber band) so that it hangs down into the water, making a water-filled chamber that you can add food coloring to. Put a few drops of food coloring into the chamber and see what happens.
Are the food coloring molecules small enough to pass through the paper towel “membrane?” What happens if you put something bigger, like popcorn kernels in the chamber? Can they pass through the small pores in the paper towel?
Do the same experiment in side-by-side jars, but fill one with ice water and the other with hot water. Does this affect the rate of osmosis or how fast the food coloring molecules diffuse throughout the water?
Think about helium balloons. If you take identical balloons and fill one with helium and the other with air, the helium balloon will shrink much faster as the smaller helium atoms diffuse out more quickly than the larger oxygen molecules.
You probably know that lots of foods are full of starch, but did you know you can test foods in your own kitchen to see what has starch and what doesn’t? You can even see how starch is broken down by your own saliva by chewing a cracker for a long time and testing it for starch.
Starch is a carbohydrate, or a long chain of glucose (sugar) molecules stuck together by chemical bonds. All plants make starch, but some contain more than others. It is the most common carbohydrate in the human diet!
Iodine usually looks brown, but when long chains of starch interact with iodine, scientists think the iodine molecules get wrapped up in the chains, as if a snake is coiling around them. This changes the way the iodine reflects light, and it starts to look black or blue, instead of reddish-brown. Sugar that is not in long chains doesn’t do the same thing to iodine.
To test for starch in your own kitchen, you’ll need iodine, an eyedropper and the food you want to test. I’d suggest table sugar, potato slices, banana slices, cucumber slices, bread or anything else that is light colored. Dilute some iodine by adding about a teaspoon (5ml) of it to a teaspoon of water (5ml.) For each sample, have a control. For example, have two slices of bread: one to drop water on and another to drop iodine on. This experiment should be done with adult supervision since iodine should not be ingested!
Add a drop of water to each control sample. Then, add a drop of iodine the other samples. Watch and wait for about 5 minutes. Can you tell which samples contain starch? The ones that contain the most starch will turn the iodine blue or black.
Now, take a cracker, chew it for a minute or so and spit it out into a dish. Mash another cracker up with water and put in another dish. Drip iodine on both of them and wait. What happens?