1. PH “potential of hydrogen ” or “power of hydrogen”

2. What is pH?
PH is a measurement of how acidic or how basic a solution is. The pH scale starts at 0 and goes up to 14. Halfway between 0 and 14 is 7, which is neutral. Compounds are acidic if they have a pH lower than 7. Compounds are basic or alkaline if they have a pH higher than 7.
So, exactly what makes a compound an acid or base?

3. Pure Water is Neutral H2O H+ + OH- H+ OH-
Pure water contains equal amounts of ions: H+ = OH-
H2O H OH-
hydrogen hydroxide ion ion H+
OH-

4. Acids Bases H+ OH- OH- H+ Have increased H+
As H+ increases, OH- decreases
[H+] > [OH-] H+
OH-
Bases
Have decreased H+
As H+ decreases, OH- increases
[OH] > [H+]
OH- H+

5. pH Scale [H+]>[OH-] [H+] = [OH-] [OH-]>[H+]
Neutral
[H+]>[OH-] [H+] = [OH-] [OH-]>[H+]
Each whole number represents
a factor of 10 on the scale.
Acidic
Basic

6. Questions
A student takes the pH of a solution with a pH meter and it reads What type of solution is this? _________. What must there be more of, hydrogen ions or hydroxide ions? _______
A student adds ammonia to the solution and the pH now reads 9.5. What type of solution is this? _________. What was released by the ammonia to cause this change? ___________
acid
hydrogen
base
hydroxide ions

7. Bleach is a strong base. Black coffee is a weak acid
Bleach is a strong base. Black coffee is a weak acid. What would happen if these two were mixed? ______________
weak base
Base
Base

8. The pH of a liquid can be measured using Litmus paper or pH paper.
Litmus Paper – shows whether a solution is an acid or base (alkaline) but doesn’t tell you how acidic or basic (alkaline); there are two different colors, red (acid) and blue (base)
PH Paper – not only tells you whether it is an acid or base (alkaline) but indicates how acidic or basic (alkaline) it is

9. Bromthymol Blue
Bromthymol blue is a chemical indicator that is blue is basic and neutral solutions and turns greenish and then yellow as the solution becomes more and more acidic.
pH = pH = 2
pH = pH = 11
blue
yellow
green
blue

10. Importance of PH to Biology:
Most cells can only survive within a certain pH range. If the pH of their body or their environment fluctuates too much the organism can die.
For example:
Human blood has a pH of about 7.35.
Any higher or lower and the blood cells
would be injured or killed.
Proteins, such as enzymes are denatured or destroyed by acids. If this happens they do not functional properly.

11. pH < 7.35
pH > 7.45
Acid
Base
Carbon Dioxide
Bicarbonate or
Acidosis vs. Alkalosis Caused by: Caused by: *slow breathing *hyperventilating *poor lung function *long periods of vomiting

12. Remember the body tries to maintain a stable constant condition which is known as homeostasis. It has several systems in place to regulate its pH levels:
Lungs: One mechanism the body uses to control blood pH involves the release of carbon dioxide from the lungs. By adjusting the speed and depth of breathing, the brain and lungs are able to regulate the blood pH minute by minute.

13. Kidneys: The kidneys are also able to affect blood pH by excreting excess acids or bases in the urine. The kidneys make these adjustments more slowly than the lungs do, usually over several days.

14. Feedback Loops
When one of the body’s systems falls out of balance in some way, a process known as negative feedback signals the problem or state of change. The body responds by regulating the necessary system with the aim of returning to homeostasis rather than going too far in the wrong direction.
In positive feedback, the body increases a change in internal conditions in order to deal with an emerging situation. For example, the body may increase white blood cell production to attack an infection.