Biology 12 Unit A The Chemistry of Life – Part 1

Properties of Water

Properties of Water Water has a high heat capacity.

Properties of Water Water has a high heat capacity. A calorie is the amount of heat energy needed to raise the temperature of 1g of water 1°C.

Properties of Water Water has a high heat capacity. A calorie is the amount of heat energy needed to raise the temperature of 1g of water 1°C. It only takes about 0.5 calories to raise the temperature of most other covalently bonded liquids 10C.

Properties of Water

Properties of Water Water has a high latent heat and heat of vaporization because of the energy needed to break H-bonds Water helps regulate temperature in organisms

Properties of Water Water is a solvent. Water has areas of partial positive and negative charge called dipoles. Dipoles attract ions to dissolve ionic compounds

Properties of Water Water molecules are cohesive and adhesive.

Properties of Water Water molecules are cohesive and adhesive. Water molecules cling together because of hydrogen bonding (cohesion).

Properties of Water Water molecules are cohesive and adhesive. Water molecules cling together because of hydrogen bonding (cohesion). Water’s positive and negative poles allow it to adhere to polar surfaces (adhesion).

Properties of Water Water molecules are cohesive and adhesive. Water molecules cling together because of hydrogen bonding (cohesion). Water’s positive and negative poles allow it to adhere to polar surfaces (adhesion). Water is an excellent transport system, both outside and within living organisms.

Properties of Water Water has a high surface tension

Properties of Water Water has a high surface tension This allows some insects to walk on the surface of a pond or lake.

Properties of Water Frozen water is less dense than liquid water. Water is at is greatest density at 4◦C H bonds form a honeycomb lattice in frozen water, spacing out the molecules. Ice insulates lakes, allowing cycling of water

Properties of Water Water acts as a lubricant Water is transparent i.e. water in saliva moistens food and lubricates the esophagus during swallowing. Water is transparent Allows algae to conduct photosynthesis under surface of water.

A1 concept check-up questions 1. what is an organic molecule? 2. Describe a polar covalent bond. 3. What causes H-bonding? What is the effect of H-bonding in water? 4. Why are water’s solvation abilities important to life?

Acids, Bases, pH and Buffers

Acids and Bases When water ionizes, it releases an equal number of hydrogen ions (H+) and hydroxide ions (OH-).

Acids and Bases

Acids and Bases Acidic Solutions (High H+ Concentrations)

Acids and Bases Acidic Solutions Acids are substances that dissociate in water, releasing hydrogen ions (H+).

Acids and Bases Acidic Solutions HCl H+ + Cl- Acids are substances that dissociate in water, releasing hydrogen ions (H+). An example: in the stomach HCl H+ + Cl- H+ helps break down protein

Acids and Bases Basic Solutions (Low H+ Concentrations)

Acids and Bases Basic Solutions Bases are substances that dissociate in water, releasing hydroxide ions (OH-) or take up hydrogen ions (H+).

Acids and Bases Basic Solutions NaOH Na+ + OH- Bases are substances that dissociate in water, releasing hydroxide ions (OH-) or take up hydrogen ions (H+). An example: NaOH Na+ + OH-

Acids and Bases H+ from acid and OH- from base neutralize each other to make water. The other ions form a salt. HCl + NaOH  H2O + NaCl Water is neutral, neither acid nor base

Acids and Bases

Acids and Bases The pH Scale

Acids and Bases The pH Scale Ranges from 0 - 14

Acids and Bases The pH Scale Ranges from 0 - 14 A pH below 7 is acidic [H+] > [OH-]

Acids and Bases The pH Scale Ranges from 0 - 14 A pH below 7 is acidic [H+] > [OH-] A pH above 7 is alkaline [OH-] > [H+]

Acids and Bases The pH Scale Ranges from 0 - 14 A pH below 7 is acidic [H+] > [OH-] A pH above 7 is alkaline [OH-] > [H+] A pH of 7 is neutral [H+] = [OH-]

The pH Scale

Acids and Bases The pH Scale Each unit change in pH represents a change of 10X the level of acidity

Buffers and pH

Buffers and pH A buffer is a chemical(s) that keep pH within normal limits. This helps maintain homeostasis in living organisms.

Buffers and pH A buffer is a chemical that keeps pH within normal limits. This helps maintain homeostasis in living organisms. Bicarbonate ions (HCO3-) and carbonic acid (H2CO3) found in human blood buffers the pH from 7.35 in muscles to 7.38 in lungs. In the stomach, pH = about 2.5

Buffers and pH OH- + H2CO3 HCO3- + H2O If hydrogen ions (H+) are added to the blood, this reaction occurs: H+ + HCO3- H2CO3 If hydroxide ions (OH-) are added to the blood, this reaction occurs: OH- + H2CO3 HCO3- + H2O Bicarbonate ions are amphiprotic, they can act as acids or bases.

A2 concept check-up questions What is the fundamental difference between an acid and a base? 2. What makes water “neutral”? 3. Is a solution with a low pH more or less acidic than one with a high pH? 4. What is the role of bicarbonate ions in the blood?