Ch 8

• Acids

  Taste sour, dissolve some metals, cause plant dye to change color
• Bases

  Taste bitter, are slippery, are corrosive
• Arrhenius theory

  • Acid - a substance, when dissolved in water, dissociates to produce hydrogen ions
  • Hydrogen ion - also called "proton"
  • HCl is an acid
• Arrhenius theory

  • Base - a substance, when dissolved in water, dissociates to produce hydroxide ions
  • NaOH is a base
• Where does NH3 fit? When it dissolves in water it has basic properties, but it does not have ions in it
• Brønsted-Lowry theory

  • Acid - proton donor
  • Base - proton acceptor
• Amphiprotic


  A substance possessing both acid and base properties
• Water is the most commonly used solvent for both acids and bases</b>
• Conjugate acid

  • What the base becomes after it accepts a proton
• Conjugate base

  • What the acid becomes after it donates its proton
• Conjugate acid-base pair

  The acid and base on the opposite sides of the equation
• Acid and base strength

  Degree of dissociation, not a measure of concentration
• Strong acids

  • HCl, HBr, HI, HNO3, H2SO4, HClO4
• Strong bases

  • NaOH, KOH, Ba(OH)2, All metal hydroxides
• Weak acids and bases

  Only a small percent dissociates (Weak electrolytes)
• Weak acids

  • Acetic acid, Carbonic acid
• Weak bases

  • Ammonia, Pyridine, Aniline
• The reversible arrow isn't always written for acid-base dissociation
• HF

  Stronger acid than HCN
• Pure water is virtually 100% molecular, with a very small number of molecules dissociating
• pH scale

  A scale that indicates the acidity or basicity of a solution, ranging from 0 (very acidic) to 14 (very basic)
• If acid is added, pH decreases, if base is added, pH increases, when equal amounts of acid and base are present, pH is neutral
• Measuring pH

  • Can be calculated if the concentration of either ion is known, approximated using indicator/pH paper, or measured using a pH meter
• Each 10-fold change in concentration changes the pH by one unit
• Importance of pH and pH control

  • Agriculture, Physiology, Acid Rain, Municipal services, Industry
• Neutralization reaction

  The reaction of an acid with a base to produce a salt and water
• Net ionic neutralization reaction

  Show only the changed components, omit any ions appearing the same on both sides (spectator ions)
• Titration

  An analytical technique to determine the concentration of an acid or base, involving the addition of a measured amount of a standard solution to neutralize the second, unknown solution
• Standard solution

  A solution of known concentration
• Equivalence point

  The point where the moles of acid and base are equal
• Indicator

  A substance which changes color as pH changes
• Solving for the concentration of a solution of hydrochloric acid


  Indicator changes color at equivalence point

  2. Determine moles of HCl present

  3. Determine volume of NaOH added from buret

  4. Calculate HCl concentration from the data
• Standard solution


  Solution of known concentration
• Acid–Base Titration

  1. Standard solution is slowly added until the color changes

  2. The equivalence point is when the moles of acid and base are equal
• Buret

  Long glass tube calibrated in mL which contains the standard solution
• Titration Experiment

  1. Place a known volume of acid whose concentration is not known into a flask

  2. Add an indicator

  3. Known concentration of base is placed in a buret

  4. Drip base into the flask until the indicator changes color
• Solving for the Concentration of a Solution of Hydrochloric Acid

  1. Indicator changes color at equivalence point

  2. Determine the moles of HCl present in the unknown acid

  3. Volume dispensed from buret is determined

  4. Calculate acid concentration from the given data
• The balanced reaction shows that 1 mol HCl reacts with 1 mol NaOH (a 1:1 ratio)
• This amount of HCl is contained in 25.00 mL
• Polyprotic substance

  Donates or accepts more than one proton per formula unit