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pH Scale & Molarity

pH Scale & Molarity. Unit 1: Biochemistry. You must know!. How to interpret the pH scale. The importance of buffers in biological systems. pH Scale. In an aqueous solution some water and other molecules tend to ionize Ex: H 2 O  H + (hydrogen ion) and OH - (hydroxide ion)

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pH Scale & Molarity

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  1. pH Scale & Molarity Unit 1: Biochemistry

  2. You must know! • How to interpret the pH scale. • The importance of buffers in biological systems.

  3. pH Scale • In an aqueous solution some water and other molecules tend to ionize • Ex: H2O  H+ (hydrogen ion) and OH- (hydroxide ion) • The concentration of H+ is used to calculate pH • The pH scale ranges from 1 - 14

  4. pH Scale • Between each number of the pH scale the H+ concentration changes 10 fold. • It is a negative, logarithmic scale pH = -log [H+] • Ex: a solution has a concentration of 10-7 Molar H+ therefore the solution has the pH = ? • Water is neither acidic nor basic, but neutral

  5. Acids • Acid • Solution that has a high concentration of H+ ions • Chemical formula usually begins with H • Has a pH of 6.9 or less • Examples: HCl, H2SO4, HNO3, HCH3O3

  6. Bases • Base • Solution that has a low concentration of H+ (high concentration of OH-) • Chemical formula usually ends with OH • Has a pH of 7.1 or higher • Examples: NaOH, KOH, Mg(OH)2 • If an acid is added to water, the pH drops • If a base is added to water, the pH rises

  7. Buffers • Buffers • Substance that keeps the pH relatively stable when an acid or base is added. • Most biological solutions have a natural ability to buffer: blood, milk, saliva, egg white • Chemical reactions in living things (respiration, photosynthesis) depend on a stable pH • Buffers add H+ ions when pH rises or remove H+ ions when pH drops

  8. Molarity • Used to determine a concentration in chemical solutions • 1M (one molar) NaCl solution means that 6 x 1023 molecules of NaCl are dissolved in 1 liter H2O. • Mass of a substance (indicated on Periodic Table of Elements): Na = __, Cl = ___ so NaCl = Na + Cl = 58 grams/mole • To make a 1M NaCl solution 58g NaCl will be dissolved in 1L water

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