Biochem LAB

• pH is a measure of how acidic or basic a chemical is when it's in an aqueous (water) solution
• A neutral pH value is 7, substances with a pH greater than 7 up to 14 are considered bases, and chemicals with a pH lower than 7 down to 0 are considered acids
• The closer the pH is to 0 or 14, the greater its acidity or basicity, respectively
• pH ranges from 0 (acidic) to 14 (basic), with a value around 7 considered neutral
• pH is measured using pH paper or a pH meter
• Most fruits, vegetables, and body fluids are acidic, while cleaners tend to be basic
• Not all liquids have a pH value; pH only has meaning in an aqueous solution
• Neutral pH chemicals include pure water, which tends to be slightly acidic due to dissolved carbon dioxide and other gases
• Common acidic substances include hydrochloric acid, battery acid, lemon juice, vinegar, apples, soda, sauerkraut, pickles, wine, beer, tomatoes, bananas, and black coffee
• Common basic substances include shampoo, human blood, human tears, egg, seawater, baking soda, toothpaste, milk of magnesia, ammonia, hair straightening chemicals, lime, lye, and sodium hydroxide
• Soil pH ranges from 3 to 10, with most plants preferring a pH between 5.5 and 7.5
• Stomach acid has a pH value of 1.2, and buffer solutions may be prepared to maintain a pH near 7
• Methods to measure pH include using pH paper test strips, pH indicators, pH test kits, and pH meters
• The pH equation is pH = -log[H], where [H] stands for the hydrogen ion concentration in moles per liter solution
• Strong acids completely dissociate in water, forming H+ and an anion, while weak acids only partially dissociate
• Examples of strong acids include hydrochloric acid, nitric acid, sulfuric acid, hydrobromic acid, hydroiodic acid, and perchloric acid
• Weak acids include hydrofluoric acid, acetic acid, and molecules containing an ionizable proton or carboxyl group
• Cations:

  • Transition metal cations
  • Heavy metal cations with high charge
• Transition metal cations include:

  • Fe^3+
  • Cu^2+
  • Zn^2+
  • Ag^+
  • Au^3+
• Heavy metal cations with high charge:

  • NH4^+
  • Dissociates into NH3 + H^+
• Strong Bases:

  • Dissociate 100 percent into the cation and OH- (hydroxide ion)
  • Examples include LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
• Weak Bases:

  • Examples include ammonia (NH3) and diethylamine ((CH3CH2)2NH)
  • Weak bases do not completely dissociate in aqueous solutions
  • Most weak bases are anions of weak acids
  • Weak bases react with water to generate OH- ions
• Buffer Solutions:

  • Made up of a weak acid and its conjugate base or a weak base and its conjugate acid
  • Maintain a pH balance that resists change when strong acids or bases are added
• Buffer Preparation:

  • Made by combining a weak acid with its conjugate base or a weak base with its conjugate acid
  • The use of conjugates gives a buffer solution its resistance to pH changes
• Buffers are solutions that resist changes in pH when limited amounts of an acid or a base are added
• Most buffers are aqueous solutions composed of roughly equal amounts of a weak acid and the salt of its conjugate base
• Buffers act as "shock-absorbers" against drastic pH changes
• Buffer action refers to the ability of buffers to resist changes in pH
• Buffer solutions are systems, usually aqueous, that resist changes in pH with the addition of small amounts of a strong acid or base
• Examples of buffer solutions include body fluids, injections & ophthalmic solutions, and commercial products
• Buffer capacity/value is the ability of a buffer system to resist pH changes
• The smaller the pH change caused by the addition of a given amount of acid or alkali, the greater the buffer capacity, and vice versa
• The average pH of human blood is 7.4, and any change larger than 0.10 pH unit may cause illness
• If the blood pH goes below 6.8 or above 7.8, it may result in death
• The body uses three buffer systems to maintain blood pH close to 7.4:

  1. Carbonic acid-bicarbonate system

  2. Dihydrogen phosphate-hydrogen phosphate system

  3. Proteins act as proton acceptors or donors
• Acidosis results when the body fails to eliminate enough CO2, while alkalosis is caused when very little CO2 is produced by the body
• Living cells contain an estimated 10,000 different kinds of molecules in an aqueous environment confined by a cell membrane
• A cell membrane is a lipid-based structure that separates a cell's interior from the surrounding environment
• Cell membranes, also known as plasma membranes, control the movement of substances into and out of the cell
• Up to 80% of the mass of a cell membrane consists of lipid material, primarily phospholipids, glycolipids, and cholesterol