I teach high school science and over the years have come up with a number of favorite experiments. Seventh graders love high school labs. We have bunsen burners at every desk and if I let them, we would be lighting those every lesson. We start with safety of course. We learn how to light a bunsen burner, how to adjust the flame from the hot blue flame to a yellow safety flame and discuss why we should not leave the burner unattended and why we should put it on a cooler, more visible yellow flame when we are not heating something.
We usually start with boiling water. This experiment has many variations. Sometimes we start with plain water. Other times we use salt water. Another time we might put ice in the beaker. I always have them use a thermometer to measure the temperature and record their results in a table. They have to write up every experiment in their lab book with a title, materials and methods, results and discussion. It is important to do this so they don't just think we are just 'playing'.
If they work well and safely we do more labs. When they muck up, we do a book lesson next time and I explain to them that they aren't being punished but they cannot do labs if they are not safe. This usually gets them to behave better in labs.
Now for the fun labs. One of my favorites is imploding aluminum cans. We put a small amount of water in the can and heat it on the burner until steam comes out. When the can is turned upside down in cold water, the steam, which has forced out the air, turns back to water, leaving a vacuum in the can. The can implodes from air pressure. Lots of fun!
My favorite substance is magnesium. There are lots of interesting experiments with magnesium. We dissolve it in acid and collect the hydrogen gas produced by holding our thumbs over the test tubes. Then we stick a match in to get a mini-explosion. Pop! The students love it. They also like burning magnesium as it burns very brightly. They have to wear safety glasses and not look directly at the flame. This experiment leads to discussions about fireworks (always a favorite year seven topic) and I then buy some sparklers and we burn those as well. I like them to test the hypothesis that oxygen is needed for a sparkler to burn. We put the sparkler in a covered container with a candle. When the candle uses up the oxygen, it dies but the sparkler keeps on burning.
We don't allow eating in labs normally but I do have a few favorite edible labs. The students love to make 'sherbet'. This demonstrates the neutralisation reaction between an acid (citric) and a base (soda bicarbonate). We mix the two together with some sugar. When they put it on their tongues it fizzes as carbon dioxide gas is produced and then they get a salty taste as the acid and base combine to create water and salt. They would do this experiment every day if I let them and make themselves sick on the sherbet. We do it once a year as a treat, at the end of a term if they have been cooperative and safe.
On a hot day near the end of the school year, we make real ice cream. This experiment shows that ice has 'latent' heat that can be released by adding salt. We can drive the temperature down to -12C and lower, which they find fascinating since this salty water is colder than the frozen ice they started with. Then we nestle a metal bowl in the salty ice and add a small amount of cream that has a few drops of vanilla in it plus some icing sugar. They have to stir and stir but it turns to the most beautiful ice cream. We discuss how people made ice cream in the 'olden days'. Then when they are finished they put their fingers in the salty ice water to get a feeling for how cold minus 12 C really is. We live in a subtropical environment so this is a revelation to them.
There are a lot of interesting experiments that can be done safely with year seven students and it stimulates them to look more closely at the world around them. We make paper airplanes and test flight designs. We make little paper helicopters and test the effects of wing length on flight time. We make simple electrical circuits and test the ability of different substances to conduct or insulate electricity. We study fish behaviour in my tanks and use microscopes to look for micro-organisms in our little school rainforest pond. Science, in my opinion, is the best subject to teach because there are so many good experiments and it is a voyage of discovery.