Acids, Bases and Buffers

Acids Polar substances will dissolve in water Some compounds tend to fall apart into their separate ions when dissolved in water. Substances that release H+ (hydrogen ions) when they are placed in water are known as acids.

Acids Tend to have a sour taste Citrus fruits Can corrode metals Can damage tissues in living things Have a pH lower than 7 React with bases to form salt and water (neutralization)

Are also polar substances Bases Are also polar substances When dissolved in water, substances that release OH- (hydroxide ions) are known as bases.

Bases Tend to have a bitter taste Do not corrode metals Makes them great drain cleaners Damage tissues in living things Have a pH higher than 7 React with acids to form salt and water (neutralization)

pH Scale The pH scale is used to measure the relative strength of acids and bases. A neutral pH = 7. pH < 7 = acids pH > 7 = bases

pH Scale The strength of acids and bases is based on the negative log of their hydrogen ion concentration For example, if the concentration of H+ in a solution is .001 (1 x 10-3) the pH of the solution is 3 This is because the negative log of 10-3 = 3. Therefore, an acid that has a pH of 2 is ten times stronger than an acid with a pH of 3.

pH Problem How many times stronger is a solution with a pH of 9 compared to a pH of 2? The difference in pH = 7 Each pH equals a strength difference of 10X 107 = 10,000,000 X stronger

Buffers Buffers are weak acids or weak bases that can release H+ or combine with H+ to either lower or raise the pH of a solution. These are very important in maintaining the proper pH of living tissues. Even a slight change in pH can be fatal to living things.