Wednesday, May 6, 2009

Acids and Bases Definitions Introduction to Key Terms & Concepts

There are several methods of defining acids and bases. While these definitions don't contradict each other, they do vary in how inclusive they are. Antoine Lavoisier, Humphry Davy, and Justus Liebig also made observations regarding acids and bases, but didn't formalize definitions.

Sulfuric acid can donate two
protons or hydrogen ions
in an aqueous solution.
Ben Mills

Svante Arrhenius

acids produce H+ ions in aqueous solutions
bases produce OH- ions in aqueous solutions

water required, so only allows for aqueous solutions
only protic acids are allowed; required to produce hydrogen ions
only hydroxide bases are allowed

Johannes Nicolaus Brønsted - Thomas Martin Lowry

acids are proton donors
bases are proton acceptors
aqueous solutions are permissible
bases besides hydroxides are permissible
only protic acids are allowed

Gilbert Newton Lewis

acids are electron pair acceptors
bases are electron pair donors
least restrictive of acid-base definitions

Properties of Acids

taste sour (don't taste them!)... the word 'acid' comes from the Latin acere, which means 'sour'
acids change litmus (a blue vegetable dye) from blue to red
their aqueous (water) solutions conduct electric current (are electrolytes)
react with bases to form salts and water
evolve hydrogen gas (H2) upon reaction with an active metal (such as alkali metals, alkalin
e earth metals, zinc, aluminum)

Properties of Bases

taste bitter (don't taste them!)
feel slippery or soapy (don't arbitrarily touch them!)
bases don't change the color of litmus; they can turn red (acidified) litmus back to blue
their aqueous (water) solutions conduct and electric current (are electrolytes)
react with acids to form salts and water

Examples of Common Acids

citric acid (from certain fruits and veggies, notably citrus fruits)
ascorbic acid (vitamin C, as from certain fruits)
vinegar (5% acetic acid)
carbonic acid (for carbonation of soft drinks)
lactic acid (in buttermilk)

Examples of Common Bases
  • detergents
  • soap
  • lye (NaOH)
  • household ammonia (aqueous)

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