Science Fair Topic Ideas in Chemistry

Alka Seltzer Science and Mentos Geysers

An Alka Seltzer tablet.
An Alka Seltzer tablet. Steven Errico/Getty Images

The old commercial “Plop, plop, fizz, fizz” can take on a new meaning when these tablets are used in a science fair project. Students can make Alka-Seltzer rockets, adjusting the amount of tablet and water to see how far they will fly or see if the water temperature affects how much fizz the tablet will create.

Another project that works on the same principle involves dropping Mentos candies into diet cola. The potassium benzoate, aspartame, and carbon dioxide gas in the diet cola combine with the gelatin and gum arabic in the Mentos to cause a foamy "geyser."

Growing Crystals for the Science Fair

Rock candy crystals.
Rock candy crystals. Jeff Kauck/Getty Images

There are a number of different types of crystals you can grow at home: Borax crystals, baking soda crystals, alum crystals and even rock candy crystals. Your student can create an experiment based on one type of crystal, changing the variables to see what makes them grow best or experiment with a combination of types to see which crystals grow the fastest, largest or clearest.

There are a wide variety of experiments that can be tested with crystals, depending on the type used or the hypothesis being tested.

Gak or Homemade Silly Putty

Homemade silly putty.
Homemade silly putty. Creative Commons

Gak, or homemade Silly Putty, is a favorite at science fairs, especially among elementary students for its gross factor. Gak is also known as a polymer which, depending on the recipe and ratio of ingredients used when you make it, can act as either a solid or a liquid. The project ideas for Gak are numerous.

Students can experiment with the ratios to see where the line between liquid and solid is, compare the Gak with store-bought Silly Putty or he hypothesize about what the Gak will be able to do.?

Fertilizer Effect on Plant Growth

Kids playing with potts in greenhouse
Klaus Vedfelt / Getty Images

How do different fertilizers affect the way plants grow? This project can be a fairly low-cost experiment, depending on what the student is trying to demonstrate. There are lots of different types of fertilizers, containing varying amounts of nitrogen, phosphorus, and potassium, in addition to other ingredients. You can test different fertilizers and see how they affect the height of a plant, the number or size of its leaves, the number of flowers, time until blooming, branching of stems, root development, or other factors.

To make this project even more complex, try using different plants and comparing which respond to each different kind of fertilizer while controlling for other factors such as needed water and sunlight.

Dissolving Salt and Sugar Science Experiments

Girl washing glass instrument en science class
Klaus Vedfelt / Getty Images

There are a few different ways to approach this science fair project. The first is to look at how the temperature of water affects the dissolve rate of salt or sugar. The second is to compare the differences in how salt and sugar dissolve in different temperatures of water. The third approach is to examine how salt and/or sugar dissolve in different types of liquid (water, milk, orange juice, etc.).

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