This experiment uses an everyday snack to teach students about fats and oils. You'll need milk, food coloring and vegetable oil. If you want to expand on this experiment, provide different fat levels of milk -- fat free, 2 percent and whole milk. Pour a cup of milk for every student. Each student should put one drop of food coloring in each corner of the glass, and one drop of oil in the center of the glass. Ask students to watch as the colors swirl and then mix. Explain to students that milk is composed of water and fat. The oil is soluble only in the fat, which creates a current. It takes a while for the swirling to commence, but ask students to keep a close eye and draw what they see.
This experiment allows each third-grader to feel like a mini scientist concocting his own potions. It has easy-to-follow directions and a short list of materials. Provide each student with baking soda, 1 cup of orange juice and 1 cup of water. The students will make their own orange soda. Have the students measure out 2 tsp. of baking soda. They will add 1 tsp. of baking soda to the cup of water and 1 tsp. to the cup of juice. Have them write down what they think is happening when they add the baking soda to the water and juice. The students should record that there was no change when the baking soda was added to water. But when it was added to the juice, they should have seen bubbles. It made orange soda. Explain to students that orange juice is an acid. When baking soda is added to an acid, you release carbon dioxide and you get a bubbly gas.
This experiment will help young children to develop a hypothesis. You will need a classroom refrigerator for this project. Ask students if they have ever noticed that once you cut an apple, the white flesh quickly turns brown. Ask them if there is a way to prevent that from happening; have them develop a hypothesis. Cut apples into four quarters. Have students place one quarter in the refrigerator and leave one on their desk. The other two quarters will each get a sprinkle of freshly squeezed lemon juice. Students will put one of the lemon-sprinkled quarters into the refrigerator and the other one on the desk. Make sure you identify which quarter is which. Check on the apples after every five minutes for half an hour. Have students record the appearance of the apples. Which quarters turned brown first, and which turned brown last? Record observations. Explain to students that once an apple is cut, its cells are torn, which releases enzymes. These enzymes react with oxygen, which turns the apples brown. The enzyme is released much more slowly in cold temperatures. Acids like lemon completely inactivate the enzyme.
Third-graders will enjoy this simple chemistry experiment that demonstrates the strength of acids in food. It doesn't require many materials and it's procedure is easy and fun -- they'll feel like spies. You need lemon juice or orange juice, which you can obtain from fresh fruits or from concentrate. Give every student a cotton swab and plain piece of paper. Ask the students to write or draw something on a white piece of paper by dabbing the cotton swab in the lemon or orange juice. After everyone has finished, allow the paper to dry. Once the papers are dry, ask students to come up one by one and hold their paper over a light bulb. The light bulb will heat the paper, and the weakened areas of the paper will turn brown, thus revealing the writing.