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pH, acids, and bases review

Key terms

pHThe measure of the hydrogen ion (H+) concentration in a solution
AcidSolution with a higher concentration of hydrogen ions than pure water
BaseSolution with a lower concentration of hydrogen ions than pure water

Reading the pH scale

The pH scale is used to rank solutions in terms of how acidic or how basic they are. It indicates the concentration of hydrogen ions (H+) and hydroxide ions (OH-) in a solution. These ion concentrations are equal in pure water, which has a pH of 7.
pH scale showing bleach (12.6), baking soda (9), blood (7.3), and lemon juice (2)
This pH value of 7 is important because it indicates a neutral solution. All other substances are compared to this neutral point. Any solution that has a pH of less than 7 is considered acidic, and anything above a pH of 7 is basic.

Common mistakes and misconceptions

  • Acids are not always dangerous. Acids sometimes have a bad reputation for being dangerous, but there are plenty of acidic substances that are useful (and even tasty!). For example, orange juice and coffee are acidic substances. In addition, though there are a few acids that you want to avoid handling (ie: hydrofluoric acid), don’t be fooled: strong bases can be damaging as well.
  • Lower pH number means stronger acid, higher pH number means stronger base. It can be a little confusing, but the lower the pH of a substance is, the stronger of an acid it is. Sometimes it is more helpful to think that the further away from neutral a substance is, the stronger it is in either the acidic or basic direction.
  • Acids and bases are not only important in chemistry. Although you may go into more detail learning about them in your chemistry class, acids and bases are extremely important to living things! In fact, most enzymes work best at a specific pH. For example, the enzyme pepsin is necessary for the digestion of proteins in the stomach, but it only functions at a very low pH. Therefore, it is important for the body to maintain an acidic environment in the stomach to make sure food gets digested well.

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