Part 1

Some Properties of Acids þ Taste sour þ Corrode metals þ pH is less than 7 þ React with bases to form a salt and water þ Produce H + (as H 3 O + ) ions in water

Some Properties of Bases  Taste bitter, chalky  Feel soapy, slippery  pH greater than 7  Produce OH - ions in water  React with acids to form salts and water

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

Acid/Base definitions Definition #1: Arrhenius (traditional) Acids – produce H + ions (or hydronium ions H 3 O + ) Bases – produce OH - ions (problem: some bases don’t have hydroxide ions!) HCl + H 2 O  H 3 O + + Cl -

Arrhenius acid is a substance that produces H + (H 3 O + ) in water Arrhenius base is a substance that produces OH - in water

Acid - a substance that accepts an electron pair Base - a substance that donates an electron pair Definition #2 – Lewis

The pH scale is a way of expressing the strength of acids and bases.  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 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

pH meter Tests the voltage of the electrolyteTests the voltage of the electrolyte Converts the voltage to pHConverts the voltage to pH Very cheap, accurateVery cheap, accurate Must be calibrated with a buffer solutionMust be calibrated with a buffer solution

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

Acid or base? HF NaOH HBr KOH NH 4 OH HCl HI Ca(OH) 2 Mg(OH) 2 Ba(OH)2 H 2 S Al(OH) 3