Water And pH

Question 1

Important Water facts

Answer 1

-most abundant cellular component, excellent nucleophile, 70% of our body mass (80% in infants), each molecule is H bonded to 4 more molecules, due to the H bonding between these molecules water has high ST, viscosity, MP, BP, heat of vaporization, etc.

Question 2

What can serve as H acceptors

Answer 2

Oxygen atoms of aldehydes, ketones, and amides

Question 3

What can serve as both H acceptors and donors

Answer 3

alcohols, carboxylic acids and amines

Question 4

Is water amphoteric?

Answer 4

Yes, because it dissociation generates both H+ and OH-

Question 5

What is pH?

Answer 5

The pH is a measurement of the acidity or alkalinity of a solution based on H+ concentration. The pH=-log[H+]

Question 6

What can almost completely dissociate into their ions in aqueous solution?

Answer 6

Strong electrolytes (salts, strong acids and bases)

Question 7

Acid

Answer 7

Substance that donates protons

Question 8

Base

Answer 8

Accepts protons

Question 9

When does pH=pKa?

Answer 9

When the conjugate acid concentration and the conjugate base concentration are equal.

Question 10

Polyprotic acids and bases

Answer 10

Can ionize to form more than one proton or hydroxyl ion per molecule of acid or base.

Carbonic acid
Phosphoric acid

Question 11

Buffer

Answer 11

One that resists a change in pH upon addition of acid or base

Two factors:
Molar conc. And pKa

Question 12

How to know which buffer is best?

Answer 12

The buffer with the pK close to desired pH at the highest possible conc.

Question 13

Buffers 2

Answer 13

Weak acids and its conjugate base mixture, they buffer cells and tissues against pH changes

Carbonate and phosphate buffers are the most important in the body

Question 14

What are the most important organs for both controlling pH and eliminating excess H+?

Answer 14

Lungs and Kidneys

Lungs: reduce pCO2 in blood increasing [HCO3-]/[CO2]

Kidneys: keep [HCO3-] right by retaining it and making more if need be, and eliminate H+ by forming NaH2PO4 and NH4+ (urine)

Question 15

How does the respiratory system control the acidity of blood?

Answer 15

Through regulating the elimination of CO2 and H20

Question 16

Hypoventilation

Answer 16

Lowers [HCO3-]/[CO2] ratio and therefore lowers pH by increasing pCO2

Question 17

Hyperventilation

Answer 17

increases the ratio and therefore increases the pH by decreasing pCO2

Question 18

Isohydric Transport

Answer 18

Transport of CO2 without generating a change in blood pH

Question 19

Chloride exchange

Answer 19

helps maintain electrical neutrality during passage of HCO3- out of and back into red blood cells.

Low [Cl-] and high [HCO3-] in tissues (venous) plasma
High [Cl-] and low [HCO3-] in lung plasma (arterial)

Question 20

How do the kidneys regulate the [HCO3-] in the blood?

Answer 20

• By adjusting the amount reabsorbed in lumen
• make more by the deamination of glutamine by glutaminase in kidney tubule cells and also oxidative deamination of other amino acids

Question 21

Transport of O2

Answer 21

Transported as oxyhemoglobin, Hb’s affinity for O2 is reduced by 2,3-bisphosphoglycerate and by decrease in pH and by CO2

Question 22

Transport of CO2

Answer 22

-15% of CO2 transported from tissues to lungs as carbamino Hb in red blood cells, only occurs in uncharged amino groups.

Question 23

Bicarbonate Buffer

Answer 23

• Most important inorganic buffer in body
• volatile acid component: CO2; which has a great affect on pH
• Both H2CO3 and CO2 considered as acid form
• [H2CO3] only 1/200 of [CO2]

Question 24

How to determine [CO2]?

Answer 24

• Concentration of gas proportional to partial pressure
• Measure partial pressure of CO2 (pCO2)
• Multiply pCO2 by conversion factor (.03 mM/ mm Hg)

Question 25

Phosphate Buffer

Answer 25

H2PO4(-) HPO4(-2) are the important forms in the body since pK 6.7 is closest to pH 7.4