According to the Middle School Portal, students in middle school should learn how to examine changes in physical states, in solutions and some chemical reactions. These are considered to be a necessary basis for their future high school studies when they learn about more diverse chemical reactions and how these are applied in practice.
Some experiments require the supervision of a teacher to ensure safety and sufficient explanation of what is happening. One popular experiment concerns finding out why some liquids that have been mixed, such as oil and vinegar, subsequently separate whereas others, such as some fizzy or soft drinks, do not. Another is to find out why some fires should be put out using a foam spray when others are best extinguished by using water.
Another experiment for middle school kids is desalination, where they are shown how easily salt can be separated from sea water. They will then discuss and consider why drinking water is not generally made in this way and the problems that exist when desalination on a large scale has been undertaken. Another associated experiment is the tension that exists in different liquids and whether adding substances such as soap increase it. Consideration and discussion can then enable students to have a wider understanding of why, for example, some insects can stand on the surface of water.
Other experiments can easily be undertaken at home using everyday household materials, under the supervision of parents. One example is a density column for liquids. You find appropriate liquids with different densities and colors and put them in a glass. Another is to use raisins in soda to make them "dance." You can also use material from around your home to make plastics or an indicator of acidity simply with the juice from a red cabbage.