Expt. 2

• According to Arrhenius theory, acid produces H+ in solutions and bases produces OH- in solution.
• The more hydrogen solution have, the more acidic it is.
• According to Arrhenius theory,

  
  

  Arrhenius acid (HA molecule) —> Hydrogen ion (acidic species) + Negative ion
• According to Lewis concept, acid is an electron pair acceptor, and base is an electron pair donor.
• According to Lewis Concept, Lewis base will give more electron to the Lewis acid making it more acidic.
• According to Bronsted-Lowry Theory, acid is a proton donor and base is a proton acceptor.
• According to Bronsted-Lowry theory, acid gives proton to base forming conjugate base and conjugate acid.
• pH = -log [H+]

  • refers to the “potential of hydrogen ion”
  • proposed by Soren Sorensen in 1909
  • defined as the negative of the logarithm of the concentration of hydrogen ion
• In the self-ionization of water, the amphiprotic ability of water to act as a proton donor and acceptor allows the formation of hydronium (H30+) and hydroxide ions (OH-).
• Ionization is the process by which ions are formed by gain or loss of an electron from an atom or molecule.
• Dissociation is the separation of a molecular entity into two or more molecular entities.
• pH Scale

  • Measure of how acidic or basic a solution is
  • often measured on a 1 to 14 range
• • pH less than 7 indicates acidic properties.
  • pH greater than 7 indicates basic properties
  • pH at exactly 7 is neutral.
• The higher the [H+], the lower the pH
• Magnesium carbonate = milk of magnesia
• • pH indicators exist as liquid dyes and dye infused paper strips. They are added to various solutions to determine the pH values of those solutions.
• • Liquid form of pH indicators is added directly to solutions.
  • Paper form is dipped into solutions and then removed for comparison against a color/pH key.
• phenolphthalein TS is a universal indicator composed of different chemical compounds. It can change color when added in a solution over a pH value ranging from 1-14 that indicates the acidic or basic property of the solution.
• TS means test solution.
• Phenolphthalein TS

  • used in qualitative analysis (uses organoleptic)
  • used for assays in monograph
• Litmus paper test

  • pH indicator paper coated with an organic dye which changes color in the presence of acids and bases
  • Litmus paper is used when determining whether a solution is acidic or basic.
  • Litmus paper does not provide accurate information regarding the strength of the acid or base.
• • Red litmus turns blue in base.
  • Blue litmus turns red in acid.
• pH paper is a strip of special paper that can be used to find approximate pH of solution based on the change of color when immersed in the solution.
• pH meter should always be calibrated before each measurement to get accurate results.
• The calibration should be performed with at least two buffer solutions with known pH.

  Buffer solution resist change in pH. For general purposes, buffer solutions with pH 4 and pH 10 are used.
• pH meter

  • After each single measurement, the bulb is rinsed with distilled water or deionized water to remove any traces of solution being measured.
  • Then, the bulb is blotted with a blotting paper to remove remaining water that could dilute the sample and alter the reading.
  • When not in use, the bulb must be kept wet at all times to avoid dehydration of the pH sensing membrane.
• pH meter can have bench type and pen type.
• Litmus paper method

  • Acetaminophen - blue to red
  • Ethanol - blue (no change)
  • Aspirin - blue to red
  • Saline solution - blue to red
• pH paper method

  • Acetaminophen - 5-6 (yellow)
  • Ethanol - 7-8 (yellow-green)
  • Aspirin - 2-3 (red)
  • Saline solution - 5-6 (yellow)
• pH indicator method

  • Acetaminophen - colorless
  • Ethanol - colorless
  • Aspirin - colorless
  • Saline solution - colorless
• Henderson-Hasselbalch Equation

  • The pH of a buffer solution can be calculated from the concentration of its acid and conjugate base using the Henderson Hasselbalch equation.
• Classification of sugar is disaccharide.
• What happens to an acid when it donates a proton according to the Brønsted-Lowry theory? It gains a proton.
• Acetic acid is a weak acid.
• Neutralization is the type of reaction occurs when an acid and base react together.
• pH Scale

  HCl, Battery acid - 0

  Stomach, sulfuric acid

  Lemon, lemon juice / vinegar

  Vinegar, orange juice / soda

  Wine, Acid rain (4.2 - 4.4) / Acidic lake (4.5)

  Coffee, Bananas (5.0 - 5.3) / Clean rain (5.6)

  Milk, Healthy lake (6.5) / Milk (6.5)

  Water

  Blood, Sea water / eggs

  Baking soda

  Milk of magnesia

  Ammonia

  Soap

  Bleach

  Drain cleaner
• Environmental effects

  • All fish die (4.2)
  • Frog eggs, tadpoles, crayfish, and mayflies die (5.5)
  • Rainbow trout begin to die (6.0)
• Acetic acid is a weak acid.
• Henderson-Hasselbalch Equation

  • Determination of the percentage of the neutral or ionic form of a weak acid or weak base at a given pH.
• Henderson-Hasselbalch Equation

  • Determination of the pKa of an acid or base.