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  • Course Biology Global - for use with NGSS (NEW)
  • Unit 1 The Chemistry of Living Things
  • Concept 1.1 Acids and Bases

    • Acids and Bases

    What are the differences between acids, bases, and buffers?

    Acids, bases, and buffers have unique properties:

    • Arrhenius defined acids as compounds that dissociate into hydrogen ions and a negative ion when dissolved in water.
    • Brønsted and Lowry defined acids as hydrogen ion donors.
    • Acids have a sour or tart taste.
    • Acids react with certain metals, producing hydrogen gas.
    • Acids react with carbonates to produce carbon dioxide gas.
    • Acids change the color of indicators.
    • Bases are found in foods, medicines, cleaning products, and in our bodies.
    • The Arrhenius definition of a baseglossary term (opens in a new window) is a compound that dissociates into a hydroxideglossary term (opens in a new window) ion and a positive ion in a solution.
    • Brønsted and Lowry defined bases as hydrogen ion acceptors.
    • Bases have a bitter taste.
    • The slippery feel of soaps is a result of bases it contains.
    • When bases mix with indicators, they change the color of the indicator.
    • Acids and bases have varying degrees of strength.
    • The strength or weakness of an acidglossary term (opens in a new window) depends on how completely it ionizes in water.
    • The measure of a substance’s acidity or basicity (also alkalinity) is its pHglossary term (opens in a new window), which stands for potential of hydrogen.
    • The pH scaleglossary term (opens in a new window) ranges from 0 to 14.
    • The values on the pHglossary term (opens in a new window) scale represent the negative logarithm of the H3O+ concentration of the substance.
    • A substance with a pH of 7 is neutral.
    • Substances with a pH that is less than 7 are acidic.
    • Substances with a pH greater than 7 are basic
    • Many pH scales are color coded according to changes in indicator colors.
    • When acids and bases of equal strength are combined, their ions combine to form a neutral solution of salt and water.
    • Combining acids and bases is commonly done to produce buffers.
    • A bufferglossary term (opens in a new window) is a solution of a weak acid and its corresponding baseglossary term (opens in a new window), or vice versa.
    • Buffers are able to resist drastic changes in pH when small amounts of acids or bases are added to them.
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