AI Tutor
If you mix hydrochloric acid and magnesium, bubbles erupt instantly. But is that gas coming from the acid, the metal, or the water they dissolved in?
To pinpoint the exact cause of any chemical phenomenon, you have to choose the right investigative tool.

Three Types of Scientific Investigations

Scientists use three distinct investigation frameworks: descriptive, comparative, and experimental.
A descriptive investigation records observations without manipulating conditions or testing relationships, such as cataloging the crystal shapes of unknown salts under a microscope.
A comparative investigation measures differences between two or more distinct groups without altering their environment, such as comparing the boiling points of ethanol versus water.
What if you want to prove that heating a solution directly causes a solute to dissolve faster?

Anatomy of an Experiment: Variables

An experimental investigation is a fair test where you deliberately alter one factor to determine if it causes a measurable change in another.
In 1668, Italian physician Francesco Redi pioneered controlled experiments by placing meat in open, sealed, and gauze-covered jars to prove maggots do not spontaneously generate.
The independent variable is the single condition you deliberately change, while the dependent variable is the responding factor you observe and measure.