ACIDS AND BASES http://www.visionlearning.com/library/module_viewer.php?mid=58

ACIDS The term acid comes from the Latin terms acere, which means “sour” and acidus, which means “sharp”. Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and become less acidic when mixed with bases. Acids are compounds that contain hydrogen and can dissolve in water to release hydrogen ions into solution. HCl H20 H+(aq) + Cl-(aq)

Uses of Acids Acetic Acid = Vinegar Citric Acid = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch. Ascorbic acid = Vitamin C which your body needs to function. Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics. Car batteries

BASES Bases feel slippery, change litmus blue, and become less basic when mixed with acids. Another word for base is ALKALI. Where have we heard that before??? Bases are substances that dissolve in water to release hydroxide ions (OH-) into solution. NaOH H20  Na+(aq) + OH-(aq)

Uses of Bases Bases give soaps, ammonia, and many other cleaning products some of their useful properties. The OH- ions interact strongly with certain substances, such as dirt and grease. Chalk and oven cleaner are examples of familiar products that contain bases. Your blood is a basic solution.

NEUTRALIZATION As you can see from the equations, acids release H+ into solution and bases release OH-. If we were to mix an acid and base together, the H+ ion would combine with the OH- ion to make the molecule H2O, or plain water (neutral substance): H+(aq)+  OH-(aq)   H2O

The neutralization reaction of an acid with a base will always produce water and a salt, as shown below: Acid + Base  Water + Salt HCl  +  NaOH  H2O  +  NaCl HBr  +  KOH   H2O  +  KBr

PREDICT: ACID OR BASE? Lemons/limes ACID

Pickles ACID

Baking soda (NaHCO3) BASE

Hand soap BASE

Ammonia (NH3) BASE

Tums BASE

Coffee ACID

Apple juice ACID

Drain cleaner BASE

Tomatoes ACID

Glass cleaner BASE

Normal rain water SLIGHTLY ACIDIC

Water (H2O) NEUTRAL

How do we measure how acidic or basic something is? Both acids and bases are related to the concentration of hydrogen ions present.  Acids increase the concentration of hydrogen ions, while bases decrease the concentration of hydrogen ions (by accepting them to form H2O).  The acidity or basicity of something therefore can be measured by its hydrogen ion concentration. This is done with the pH scale.

The pH scale is described by the formula: pH = -log [H+] Note: concentration is commonly abbreviated by using square brackets, thus, [H+] = hydrogen ion concentration.  When measuring pH, [H+] is in units of moles of H+ per liter of solution.

What does THAT mean? For example, a solution with [H+] = 1 x 10-7 moles/liter has a pH equal to 7 (a simpler way to think about pH is that it equals the exponent on the H+ concentration, ignoring the minus sign). [H+] = 1 x 10-7 plugged into the equation is: -log [1 x 10-7] = -log10 [-7] = -(-7) = 7

Measuring pH The pH scale ranges from 0 to 14. Substances with a pH between 0 and less than 7 are acids (pH and [H+] are inversely related - lower pH means higher [H+]). Substances with a pH greater than 7 and up to 14 are bases (higher pH means lower [H+]). Right in the middle, at pH = 7, are neutral substances, for example, pure water.

The pH scale

A change of 1 pH unit represents a tenfold change in the acidity of the solution. For example, if one solution has a pH of 1 and a second solution has a pH of 2, the first solution is not twice as acidic as the second—it is ten times more acidic

What is the pH? Is it acid/base/neutral? -log [1 x 10-9] -log [1 x 10-7] [H+] = 1 x 10-3 [H+] = 1 x 10-13 base pH = 9 neutral pH = 7 pH = 3 acid pH = 13 base