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Biology I What is pH?

Biology I What is pH?. Acids and Bases. Some of our favorite foods make our tongue curl up because they are SOUR. Bitter!. Some foods have a “ bite ” of their own because they ’ re somewhat bitter. WHY?. Acidic/Basic. There is a scientific reason for this:

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Biology I What is pH?

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  1. Biology IWhat is pH?

  2. Acids and Bases • Some of our favorite foods make our tongue curl up because they are SOUR.

  3. Bitter! • Some foods have a “bite” of their own because they’re somewhat bitter. • WHY?

  4. Acidic/Basic • There is a scientific reason for this: • These foods are either acidic or basic. • The degree of acidity or alkalinity (basic) is important in organisms.

  5. Acids and Bases • Chemicals may be classofied as acids or bases. • Things that are neither acids nor bases are neutral. • pH measures how acidic or basic a solution is.

  6. Acids • Often taste sour • Strong acids can burn skin & eyes • Strong acids can dissolve metals • Examples: • Lemon juice • Vinegar • Car battery acid (dangerous!)

  7. Bases • Can taste bitter, sweetish, or salty • Strong bases can burn skin & eyes • Bases are often used for cleaning • Examples: • Milk • Baking soda • Soap • Drain cleaner (dangerous!)

  8. Some substances are not really an acid or a base: For example, pure water

  9. pH • A special name is given to the acid or base characteristic that a substance has: • It is called: pH • “p” stands for potential and “H” stands for hydrogen; hence, the potential of a substance to attract hydrogen ions

  10. Acid • Any substance which has a pH of value of less than 7 is considered an acid • Proton donors • This means that the number of hydronium (H3O+ ) ions is greater than the number of hydroxide ions (OH-). 0--------------7---------------14 Acid Neutral Base

  11. Base • Any substance which has pH value greater than 7 is a base • Proton acceptors • This means that the number of hydroxide (OH-) ions in a solution is greater than the number of hydronium (H3O+ ) ions. 0--------------7---------------14 Acid Neutral Base

  12. pH 7 • A pH of 7 is called neutral—neither acid nor base. 0------------7------------14 Acid Neutral Base

  13. The pH Scale • Compares the relative concentration of H3O+ ions and OH- ions • Scale ranges from 0 to 14; 0-3 is very acidic; 7 is neutral; 11-14 is very basic or alkaline • Litmus paper, phenolphthalein, pH paper, & other indicators that change color can be used to measure pH

  14. pH • Using litmus paper: An acid turns blue litmus paper red and a base turns red litmus paper blue.

  15. pH scale • Scale for comparing the relative concentrations of hydronium ions and hydroxide ions in a solution • Scale ranges from 0 to 14

  16. pH • The lower the pH the stronger the acid • The higher the pH the stronger the base • pH 7.0 is neutral

  17. Buffers • Control of pH is important to organisms • Enzymes function only within a narrow pH range; usually neutral • Buffers neutralize acids or bases in organisms to help control pH

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