Water, acids, and bases

This course is a part of AP®︎ Biology, a 38-course Topic series from Khan Academy.

Where would we be without water? Well, we probably wouldn't exist at all! Learn more about this fascinating molecule: its hydrogen bonds, its properties, and why it's a key ingredient for biological systems of all sizes. Plus, brush up on the acid-base chemistry that takes place in water (and learn how it works in your own bloodstream)!

This course contains 4 segments:

Hydrogen bonding in water

Water is key to life, and hydrogen bonding is key to understanding water! Learn how the structure of water and the properties of O and H atoms allow water molecules to "stick" to each other via hydrogen bonds, as well as why water makes a great solvent (why you can dissolve stuff in it so well).

Cohesion and adhesion

Water molecules like to stick together! Learn more about the cohesive (and adhesive) properties of water and why they're important for bugs, trees, and the tear ducts in your eyes!

Temperature and state changes in water

Ever wonder why sweating cools you off? Or why ice cubes float in a glass? If so, you're in the right place! Learn about what happens to water when it heats up, cools down, and changes state (becoming a solid or a gas). We'll see why water is great at resisting changes in temperature, and why ice is less dense than liquid water.

Acids, bases, and pH

You may know that lemon juice is acidic, and that bleach is basic. But did you know that acid-base chemistry is happening all the time in your body? Learn what makes something an acid or base, what the pH scale really measures, and how buffers work in your blood!