pH Biotechnology I 5/28/2018

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 Property of CTE Joint Venture 5/28/2018

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) Property of CTE Joint Venture 5/28/2018

Pure water naturally dissociates to produce hydrogen ions (H+) and hydroxide ions (OH-) H20 H+ + OH- Dissociation of Water Property of CTE Joint Venture 5/28/2018

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

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- Property of CTE Joint Venture 5/28/2018

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 Property of CTE Joint Venture 5/28/2018

Practice Problem The [OH-] is 1 x 10 -9. What is the H+ concentration? Property of CTE Joint Venture 5/28/2018

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 Property of CTE Joint Venture 5/28/2018

What is the pH of a solution with an H+ ion concentration of 10-4 M? Practice Problem Property of CTE Joint Venture 5/28/2018

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

pH scale- varying concentration of H+ and OH-

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

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

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

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 Property of CTE Joint Venture 5/28/2018

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 Property of CTE Joint Venture 5/28/2018

HCl is a strong acid that completely dissociates in water HCl  H+ + Cl- What is the pH of 0.1 M HCL? Practice Problem

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

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 Property of CTE Joint Venture 5/28/2018

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 Property of CTE Joint Venture 5/28/2018