The Chemistry of pH

2010

What do we know?

• pH is a scale that runs from 0-14

• Acids (<7) or base (>7)

• Water is neutral (7)

• Measures the concentration of H+ (and OH-) in solution

• Logarithmic scale: A pH of 5 is 10x more acidic than a pH of 6

The Power of H+

• What is a hydrogen ion?– A hydrogen atom that gave up its electron– Now just a proton

• How does it affect living How does it affect living things?things?

- Proteins have many H-bonds - Proteins have many H-bonds that determine their shape and that determine their shape and so they’re susceptible to pH so they’re susceptible to pH shiftsshifts

pH Scale

pH 0 = 1 mole/literpH 0 = 1 mole/liter

pH 7 = 1/10,000,000 pH 7 = 1/10,000,000 moles/litermoles/liter

pH 14 = pH 14 = 1/100,000,000,000,000 1/100,000,000,000,000 moles/litermoles/liter

Molarity (you won’t be tested on this):

• A mole is equal to 6.022 x 1023

• A 1 molar solution =1 mol/liter

• It is determined by taking the molecular weight of the molecule and adding that number of grams to 1 liter of water.

• Acid– A substance that increases the H+

concentration of a solution– HCl H+ + Cl-

• Strong: dissociates completely & irreversibly• Weak: do not dissociate completely

• Base– A substance that reduces the H+

concentration of a solution– NaOH Na+ + OH-

• Strong: dissociates easily, quickly ties up H+ • Weak: incomplete dissociation, accepts few H+

Buffer

• A substance that minimizes changes in the conc. of H+ in a solution

• Weak acids or bases that combine reversibly – Bind to H+ when pH drops– Release H+ when pH rises

Blood pH

• Ranges from 7.35-7.45

• 7.45+ is Alkalosis

• 7.0-7.35 is Acidosis

Carbonic Acid-Bicarbonate Buffering System of the Blood

pH of other body fluids

• Gastric juice HCl (stomach acid) (~2)

• Urine (5-8)– Basic in bacterial infection– Vegetarian diet

• Saliva (~6.5)

Where is acid produced?

• Breakdown of P-containing proteins

• Lactic acid (anaerobic respiration)

• Fat metabolism

• CO2 in blood

• And HCl in the stomach (but technically not in your body fluids)

Lines of defense

1. Chemical buffers– Carbonic Acid-Bicarbonate, proteins in blood, etc.– Respond in a fraction of a second

2. Respiratory center in the brainstem– Control breathing rate (CO2 a source of acid)– 1-3 mins– What will it do if blood is too acidic?

3. Kidneys– Secreting or reabsorbing H+

– Slow to respond (1 day or more)