1. pH
Biotechnology I
5/28/2018

2. Introductory Question
Write the chemical formula of water and give three (3) different examples of how water is used at your home to make solutions
Introductory Question
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3. Essential Question(s)
What role does water play in the production of hydrogen ions and hydroxide ion?
What distinguishes acids and bases?
What are common acids and bases used in a Biotech lab?
Essential Question(s)
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4. Pure water naturally dissociates to produce hydrogen ions (H+) and hydroxide ions (OH-)
H20 H+ + OH-
Dissociation of Water
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5. Significance to Biotechnology
Proper pH essential to living systems
Examples
Animals die if their blood pH deviates significantly from neutral pH
Key proteins denature at wrong pH
Microorganisms require their growth medium to be a specific pH
Industrial processes such as food processing are sensitive to pH
As a result, important to monitor and maintain proper pH
Significance to Biotechnology

6. Concentration of H+ and OH-
[ H+][OH-] =10-14
The brackets represent concentration of the respective ion
Ion = atom(s) carrying a charge
The concentration is in Molarity and expressed as powers of ten.
The exponents of ten for H+ and OH- must add to -14
10-14 a constant
Concentration of H+ and OH-
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7. Concentration of H+ ions is the same as concentration of OH- ions
[H+] =[OH-] = 1x 10-7 M
Know that [ H+][OH-] =10-14 M
Then [1x 10-7 M][1x 10-7 M] =10-14 M
Neutral pH =7
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8. Practice Problem The [OH-] is 1 x 10 -9. What is the H+ concentration?
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9. Definition of pH pH =-log [H+] For example, water [H+] of water = 10-7
The log of 1 x 10-7 = -7
The negative log of 10-7 = -(-7) =7
The pH of pure water is 7
Definition of pH
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10. What is the pH of a solution with an H+ ion concentration of 10-4 M?
Practice Problem
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11. pH Scale Use logarithms to make scale more compact
pH scale increase/decrease by a power of ten
Below 7-acidic
Above 7-basic
pH 7 neutral; [H+]=[OH-]
pH Scale

12. pH scale- varying concentration of H+ and OH-

13. Compound with a base solution of pH 11, the same volume of an acidic solution at pH 5 has __________ times as many hydrogen ions.
Compound with a acidic solution of pH 2, the same volume of a basic solution at pH of 10 has ______________ times as many hydroxide ions.
Practice Problem

14. Acids When acids added to water they release H+ ions to the solution
Increases H+ concentration
H+ > OH- considered an acidic solution
pH < 7
Example: HCl
HCl  H+ + Cl-
Acids

15. When bases are added to water, they can increase the pH in one of two ways
Reduce hydrogen ion concentration
Ex. NH3 + H+  NH4+
Increase hydroxide ion
Ex. NaOH  Na+ + OH-
pH > 7; [H+] < [OH-]
Bases

16. Strong acids/bases completely dissociate when dissolved in water
HCl in water  H+ + OH- (all in this form)
NaOH in water  Na+ + OH- (all in this form)
As a result, they have a strong effect on pH
Strong Acids/ Bases
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17. Weak acids/bases Do not completely dissociate in water
Have a smaller effect on pH
Example: acetic acid
CH3COOH in water  H+ + CH3COO-
(Most of acid stays acetic acid form)
For example, acetic acid forms about one hydrogen ion for every 100 molecules of acetic acid
Weak acids/bases
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18. HCl is a strong acid that completely dissociates in water
HCl  H+ + Cl-
What is the pH of 0.1 M HCL?
Practice Problem

19. Measurements show that the pH of a buffered solution is 4
Measurements show that the pH of a buffered solution is 4.0 What is the hydrogen ion concentration of this buffered solution? What is the hydroxide ion concentration?
Practice Problem

20. Common Acid and Bases Nitric Acid, HNO3 Hydochloric Acid, HCl
Common Acids:
Nitric Acid, HNO3
Hydochloric Acid, HCl
Acetic Acid, HC2H3O2
Common Bases:
Sodium Hydroxide, NaOH
Potassium Hydroxide Acid, KOH
Ammonia, NH3
Common Acid and Bases
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21. You are making a solution and you want to : a) lower the pH (smaller numbers). Explain what you would add and why it would lower the pH b) raise the pH (larger numbers). Explain what you would add and why it would raise the pH
Closure
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