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Skip Navigation LinksKCC Home > Academic Departments > Biological Sciences > 11New > Webpages > Unit 3, Lesson 9

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Anatomy and Physiology I
Unit 1: Introduction to Human Anatomy and PhysiologyExpand Unit 1: Introduction to Human Anatomy and Physiology
Unit 2: The Cell and It’s EnvironmentExpand Unit 2: The Cell and It’s Environment
Unit 3: Cellular ChemistryExpand Unit 3: Cellular Chemistry
Unit 4: Biomolecules, Cell Architecture and Cellular Molecular FunctionExpand Unit 4: Biomolecules, Cell  Architecture and Cellular Molecular Function
Unit 5: Tissues, Membranes and GlandsExpand Unit 5: Tissues, Membranes and Glands
Unit 6: Integumentary SystemExpand Unit 6: Integumentary System
Unit 7: Skeletal System
Unit 8: Muscular System
Unit 9: Nervous System Introductory Concepts
Unit 10: The Central Nervous System - The Spinal Cord
Unit 11: The Central Nervous System - The Brain
Unit 12: The Autonomic Nervous System and Smooth Muscle

Lesson 9 - Acids, Bases and the Concept of pH

Student Performance Objectives
1. Define the meaning of pH and explain the pH scale.
2. Explain why each unit of change of pH is a 10-fold change in hydrogen ion concentration.
3. Explain the importance of the low pH of gastric juice.
4. Explain the importance of the stomach's mucus coating and the importance of sodium
    bicarbonate secretion by the pancreas in the normal course of digestion.
5. Explain what a buffer is and give 2 examples.


Lesson Outline
A. The concept of the hydrogen ion and hydroxyl ion as ionization products of water.
B. An acid as a hydrogen ion (proton) donor.
C. A base (alkali) as a proton accepter.
D. The pH scale
    1. Extending from 0-14, as logarithmic scale so that one unit difference in pH is a 10 fold
        difference in hydrogen ion concentration (or acidity). pH 7 as the neutral point. To
        see the pH of natural substances, go to http://www.johnkyrk.com/pH.html
    2. DEMONSTRATION: the point is to demonstrate the differences in pH of natural
        substances. Using a pH meter and/or pH paper determine the pH of freshly distilled
        water, distilled water, vinegar, dilute HCl, lemon juice, soda of some type, milk, sea
        water, milk-of-magnesia, Clorox, soap solution, windex, ammonia. The students keep
        a chart of the tested substances. Ask the students how we survive since we ingest
        foods and beverages of such widely varying pH.
            Explain that the stomach is an acid vat much more powerful than any acid content
        in foods we eat and that this acid destroys most microorganisms and dissolves
        minerals out of our food. Explain how important it is for the stomach to be coated with
        mucus to protect it from our own secreted acid. Then in the small intestine, sodium
        bicarbonate from the pancreas neutralizes the stomach's hydrochloric acid.
    3. If the students have a background from previous chemistry you can explain pH more
        deeply.
        a. Since one in every 10 million water molecules, in pure water, is ionized into
            H+ and OH-, then the actual concentration of H+ in pure water is 0.0000001
            molar or 10-7 M.
        b. Since pH is technically defined as the negative logarithm of the hydrogen ion
            concentration, then -log [.0000001] = 7.
    4. Concept of a buffer - chemical solutions that resist changes in pH and which help to
        establish the pH of the solution. Examples: proteins, bicarbonate buffer, phosphate
        buffer, hemoglobin buffer.










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