1. Biology 12 Unit A The Chemistry of Life – Part 1

2. Properties of Water

3. Properties of Water
Water has a high heat capacity.

4. 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.

5. 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.

6. Properties of Water

7. 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

8. 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

9. Properties of Water
Water molecules are cohesive and adhesive.

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

11. 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).

12. 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.

13. Properties of Water
Water has a high surface tension

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

15. 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

16. 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.

17. 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?

18. Acids, Bases, pH and Buffers

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

20. Acids and Bases

21. Acids and Bases
Acidic Solutions (High H+ Concentrations)

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

23. 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

24. Acids and Bases
Basic Solutions (Low H+ Concentrations)

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

26. 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-

27. 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

28. Acids and Bases

29. Acids and Bases
The pH Scale

30. Acids and Bases
The pH Scale
Ranges from

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

32. 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+]

33. 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-]

34. The pH Scale

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

36. Buffers and pH

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

38. 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

39. Buffers and pH OH- + H2CO3 HCO3- + H2O
If hydrogen ions (H+) are added to the blood, this reaction occurs:
H+ + HCO 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.

40. 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?