• UNIT 1. INORGANIC CHEMISTRY
  • UNIT 2. INTERMOLECULAR FORCES, WATER, AND ACIDS AND BASES
  • UNIT 3. CARBOHYDRATES
  • UNIT 4. LIPIDS, NUCLEIC ACIDS, AND PROTEINS
  • UNIT 5. CELL MEMBRANES-STRUCTURE AND CELL FUNCTION
  • UNIT 6. PROKARYOTES AND VIRUSES
  • UNIT 7. ENERGY BALANCE
  • UNIT 8. GLYCOLYSIS AND CITRIC ACID CYCLE
  • UNIT 9. ELECTRON TRANSPORT CHAIN
  • UNIT 10. PHOTOSYSNTHESIS
  • UNIT 11. CELLULAR TRANSPORT AND CELLULAR SIGNALING
  • UNIT 12. CELL DIVISION AND CANCER
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  • 2.3.1

    Acids and Bases

    In pure water at 25o C, the concentration of H+ is always equal to the concentration of OH-. Both have a concentration of 1.0 x 10-7 Molar. (Placing the symbol for a chemical in brackets [H+] is chemical shorthand for “concentration of.” Therefore, [H+] is read “the concentration of hydrogen ion.”) If we add a substance that results in an increase in [H+], we say that substance is an acid. If we add a substance that results in a decrease in [H+], we say that substance is a base. An acid is any substance that, when added to an aqueous solution, increases the [H+] of the solution, and a base is any substance that, when added to an aqueous solution, decreases the [H+] of the solution. A common acid, for example, is hydrochloric acid, HCl. When HCl reacts with water, it dissociates into an H+ and a chloride ion (Cl-), thus increasing the [H+]. HCl is considered a strong acid because when placed in water, it completely dissociates into its two ions.

    HCl H+ + Cl-

    A weak acid, such as acetic acid (CH3COOH), dissociates into H+ and CH3COO- (acetate). However, most remains intact as acetic acid, and there is a chemical equilibrium between the CH3COOH and the H+ + CH3COO-. The conjugate base is the name given to the now unprotonated compound (acetate). Thus, the disassociation of acetic acid (weak acid) produces acetate (conjugate base) and a hydrogen ion:

    CH3COOH ←→ H+ + CH3COO-

    An example of a base is ammonia (NH3), which will combine with H+ to form an ammonium ion (NH4+), thus removing H+ from the solution.

    NH3 + H+ NH4+

    Another common base is sodium hydroxide (NaOH). How is this a base? When it dissolves, it dissociates into a sodium ion (Na+) and OH-, no change in [H+], right? However, the OH- will combine with H+ to form water, thus removing H+ from the solution.

    NaOH Na+ + OH-

    H+ + OH- H2O

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