Acids & Bases

The Chemistry of Acids and Bases

Acid and Bases

Acids and Bases

Acid and Bases

Acids Have a sour taste. Vinegar is a solution of acetic acid. Citrus fruits contain citric acid. React with certain metals to produce hydrogen gas. React with carbonates and bicarbonates to produce carbon dioxide gas. Hydrogen ions are formed with the acid HNO3 is dissolved in water Have a bitter taste. Feel slippery. Many soaps contain bases. Make soaps and detergents Bases

Some Properties of Acids þ Produce H + (hydrogen ion) in water solution þ Bases have a lower concentration þ Taste sour þ Corrode metals “eat away” þ Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”

Some Properties of Bases  Produce OH - (hydroxide ) ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Basic Blue”

Some Common Bases NaOHsodium hydroxidelye KOHpotassium hydroxideliquid soap Ba(OH) 2 barium hydroxidestabilizer for plastics Mg(OH) 2 magnesium hydroxide“MOM” Milk of magnesia Al(OH) 3 aluminum hydroxideMaalox (antacid) Al(OH) 3 aluminum hydroxideMaalox (antacid)

The pH scale is a way of expressing the strength of acids and bases. The pH scale measures the concentration (amount) of hydrogen ions. Instead of using very small numbers, we just use the NEGATIVE power of 10 on the Molarity of the H + (or OH - ) ion. Under 7 = acid 7 = neutral Over 7 = base

pH Scale When the concentration of hydrogen ions is high, the pH would be expected to be lower than 7. If a substance had a pH of 11, what could you predict about is Hydrogen ion concentration? –It would be low

Neutralization –A reaction between an acid and a base. In a reaction of an acid with a base, the pH changes to a value that is closer to? –7 If soap is a base, which pH levels would be the most appropriate for soap? –Anything greater than 7

pH of Common Substances

pH testing There are several ways to test pHThere are several ways to test pH –Blue litmus paper (red = acid) –Red litmus paper (blue = basic) –pH paper (multi-colored) –pH meter (7 is neutral, 7 base) –Universal indicator (multi-colored) –Indicators like phenolphthalein –Natural indicators like red cabbage, radishes

Paper testing Paper tests like litmus paper and pH paperPaper tests like litmus paper and pH paper –Put a stirring rod into the solution and stir. –Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper –Read and record the color change. Note what the color indicates. –You should only use a small portion of the paper. You can use one piece of paper for several tests.

pH indicators Indicators are dyes that can be added that will change color in the presence of an acid or base. Some indicators only work in a specific range of pH Once the drops are added, the sample is ruined Some dyes are natural, like radish skin or red cabbage