Many fun and interesting science experiments are also safe for kids. This is a collection of science experiments and projects that are safe enough for kids to try, even without adult supervision.
Learn about recycling and how paper is made by making your own decorative paper. This science experiment/craft project involves non-toxic materials and has a relatively low mess-factor.
The mentos and soda fountain, on the other hand, is a project with a high mess factor. Have kids try this one outdoors. It works with regular or diet soda, but clean-up is much easier and less sticky if you use diet soda.
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Any of several safe household substances can be used to make invisible ink. Some of the inks are revealed by other chemicals while others require heat to reveal them. The safest heat source for heat-revealed inks is a light bulb. This project is best for kids age 8 and older.
This science experiment uses hot tap water and a kitchen spice to grow crystals overnight. The crystals are non-toxic, but they aren't good to eat. I'd use adult supervision with very young children, since there is hot tap water involved. Older kids should be fine on their own.
A chemical volcano made using baking soda and vinegar is a classic science experiment, appropriate for kids of all ages. You can make the cone of the volcano or can cause the lava to erupt from a bottle.
Experiment with density, gases and color. This rechargeable 'lava lamp' uses non-toxic household ingredients to create colored globules that rise and fall in a bottle of liquid.
There are many recipes for slime, ranging from the kitchen ingredient variety to chemistry-lab slime. One of the best types of slime, at least in terms of gooey elasticity, is made from a combination of borax and school glue. This type of slime is best for experimenters who won't eat their slime. The younger crowd can make cornstarch or flour-based slime.
Experiment with color and miscibility by making water fireworks. These "fireworks" don't involve any fire. They simply resemble fireworks, if fireworks were underwater. This is a fun experiment involving oil, water and food coloring that is simple enough for anyone to do and produces interesting results.
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Experiment with freezing point depression by making your own ice cream. You can make ice cream in a baggie, using salt and ice to lower the temperature of the ingredients to make your tasty treat. This is a safe experiment that you can eat!
Experiment with detergents and learn about emulsifiers. This experiment uses milk, food coloring and dishwashing detergent to make a swirling wheel of color. In addition to learning about chemistry, it gives you a chance to play with color (and your food).