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The pH Scale

The pH Scale. What is it, and why do we care about it?. This lecture covers CA standard 1b. Why do we care about pH?. Life depends on chemical reactions

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The pH Scale

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  1. The pH Scale • What is it, and why do we care about it? This lecture covers CA standard 1b

  2. Why do we care about pH? • Life depends on chemical reactions • Most chemical reactions are carried out by enzymes. Enzymes are molecules that bring other molecules and compounds together so they can react. • Enzymes depend on a specific pH range

  3. So why do we care? • Because life depends on a certain pH range, and if you mess it up you’re in trouble.

  4. So what is pH • pH stands for potential hydrogen • The pH scale runs from 1 to 14. • Scales measure things- The pH scale indicates the amount of two different ions: H+ (hydrogen ions) and OH- (hydroxide ions)

  5. Some substances give up hydrogen ions in water (H+). These are said to be acids, because they increase the number of free hydrogen ions. • Ex: Hydrochloric acid (HCl) • Draw HCL reacting with water • Acidic solutions have a pH of 1-6.9

  6. Some substances give up hydroxide ions in water (OH-). These are said to be bases, because they increase the number of free hydroxide ions. • Ex: Sodium hydroxide (NaOH) • Draw NaOH reacting with water • Basic solutions have a pH of 7.1-14

  7. A pH of 7.0 is neutral Here’s the catch: see the board and take your own notes for the rest of the pH scale (and then its on to buffers!)

  8. To resist changes in pH, organisms have buffers • A buffer reacts with an acid or base to keep the pH constant.

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