1. pH Scale & Molarity Unit 1: Biochemistry

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

3. pH Scale In an aqueous solution some water and other molecules tend to ionize In an aqueous solution some water and other molecules tend to ionize –Ex: H 2 O  H + (hydrogen ion) and OH - (hydroxide ion) The concentration of H + is used to calculate pH The concentration of H + is used to calculate pH The pH scale ranges from 1 - 14 The pH scale ranges from 1 - 14

5. pH Scale Between each number of the pH scale the H + concentration changes 10 fold. Between each number of the pH scale the H + concentration changes 10 fold. It is a negative, logarithmic scale 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 = ? 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 Water is neither acidic nor basic, but neutral

6. Acids Acid Acid –Solution that has a high concentration of H + ions Chemical formula usually begins with H Chemical formula usually begins with H Has a pH of 6.9 or less Has a pH of 6.9 or less Examples: HCl, H 2 SO 4, HNO 3, HCH 3 O 3 Examples: HCl, H 2 SO 4, HNO 3, HCH 3 O 3

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

8. Buffers 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 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 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 Buffers add H + ions when pH rises or remove H + ions when pH drops

9. Molarity Used to determine a concentration in chemical solutions Used to determine a concentration in chemical solutions 1M (one molar) NaCl solution means that 6 x 10 23 molecules of NaCl are dissolved in 1 liter H 2 O. 1M (one molar) NaCl solution means that 6 x 10 23 molecules of NaCl are dissolved in 1 liter H 2 O. Mass of a substance (indicated on Periodic Table of Elements): Na = __, Cl = ___ so NaCl = Na + Cl = 58 grams/mole 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 To make a 1M NaCl solution 58g NaCl will be dissolved in 1L water