Acids & Bases Svante Arrhenius (1887)  ACIDS  Turn indicator dye litmus from blue to red  React with active metals such as zinc, iron, and tin, dissolving the metal and producing hydrogen gas  Taste sour, if diluted enough to be tasted safely  React with certain compounds called alkalis or bases to form water and compounds called salts  BASES  Turn the indicator dye litmus from red to blue  Feel slippery or soapy on the skin  Taste bitter  React with acids to form water and salts

Acids  Arrhenius proposed that these characteristic properties of acids are actually properties of the hydrogen ion (H + ), and that acids are compounds that yield H + in aqueous solutions.  Slightly modified today  Hydronium ion (H 3 O + )  For simplification, we’ll stick with the H + terminology.

Acids  Monoprotic  One H +  Diprotic  Two H +  Triprotic  Three H +  Polyprotic  General term for acids that give up more than one H +  Strong Acids  Ionize completely (or nearly completely) in water  HCl (hydrochloric acid)  Weak Acids  Ionize only slightly in water  CH 3 COOH (acetic acid)

Bases  Yield hydroxide ions (OH - ) in aqueous solutions  Monobasic  One hydroxyl anion  Dibasic  Two hydroxyl anions  Tribasic  Three hydroxyl anions  Polybasic  General term for bases that give up more than one OH -  Strong Bases  Completely ionize  NaOH (sodium hydroxide; lye)  All the bases of Group I and Group II are strong bases  Weak Bases  NH 3 (ammonia)

pH Scale  pH = -log [H + ]

Brønsted-Lowry Acid-Base Theory  By the 1920’s chemists were working with solvents other than water.  Acid  Proton (H + ) donor  Base  Proton (H + ) acceptor

Acid-Base Titrations  Method used to determine just how much acid (or base) there is in a solution of unknown concentration  Burette  A piece of laboratory glassware designed to deliver known amounts of liquid into another container

Acid-Base Titrations  One mole of NaOH will react completely with one mole of H +  Using volumetric analyses with a pH indicator, you can determine the moles of H +

A Word About Moles….  A mole used in chemistry is something like the dozen we use every day.  A mole simply means that you have 6.02 x of whatever you’re talking about.  Avogardo’s number  Molarity is defined as the number of moles of solute divided by the number of liters of solution  Molarity (M) = moles of solute  liters of solution

Water Hardness  Calcium (Ca 2+ )  Magnesium (Mg 2+ )  Why the concern?

Types of Water Hardness  Temporary  Permanent

EDTA  Ethylenediaminetetracetic acid  Chelating agent

Eriochrome Black T (EBT)

Example Calculations  50.0 mL sample of tap water analyzed  Beginning volume of EDTA = mL  End volume of EDTA = 6.23 mL  Amount of EDTA titrated = mL  Questions: 1. How many moles of EDTA were used? 2. What is the molarity of metal ion present in the water? 3. What is the concentration of CaCO 3 in ppm in the water?

1. How many moles of EDTA were titrated? Molarity of EDTA = M Moles of EDTA = (Molarity)(Liters of solution) = ( mol/L)( L) = moles EDTA = x moles EDTA

2. What is the molarity of the metal ion present in the water? Molarity of metal ion = moles of EDTA liters of water sample = mol EDTA L water = mol/L of EDTA = mol/L metal ions

3. What is the concentration of CaCO 3 in ppm in the water? CaCO 3 ppm = Molarity of metal ion X molecular weight of Ca 2+ X 1000 mg/g CaCO 3 ppm = mol/L X g/mol X 1000 mg/g CaCO 3 ppm = 131 mg/L = 131 ppm