AcidBaseBalanceProblems：酸碱平衡的问题.doc

6Acid Base Balance ProblemsWilliams, J. B.EEOB 410 Discussion week 2These questions are designed to give you some experience with the concept of pH, and the Henderson-Hasselbalch equation. pH stands for log H, where H is the hydrogen ion concentration in mol/L. In reality we will see that pH means the hydrogen ion activity in solution. The HH equation is fundamental to the quantitative treatment of acid-base balance. pH = pK + log HCO3S (PCO2)Where, pK is the equilibrium constant for the reaction: CO2 + H2O HCO3- + H+pK of of this reaction in blood plasma is about 6.1S the solubility of CO2 in plasma at 37oC is about 0.03 mmol/L mmHgand p is the partial pressure of CO2. The units of the pressure is usually given in the medical literature as mmHg, but these units are not SI units. But for now, we are stuck with them.1. What is the normal concentration of CO2 in arterial blood if in the lungs the pCO2 is 40 mmHg?0.03 mmoles/L mmHG(40 mmHg) = 1.2 mM/L2. At a pCO2 of 40 mmHg, what is the pH of plasma when the concentration of bicarbonate is 24 mmol/L?pH = 6.1 + log(24/1.2) = 7.43. By how much does the pH change in the above question if the bicarbonate concentration is halved?pH=6.1 + log(12/1.2) = 7.17.4-7.1 =0.34. What is the concentration of hydrogen ions in plasma with a pH of 7.4?pH= -logH+7.4 = -logH+H+=10-7.4H+ = 3.98 x 10-8 mol/L5. Give the equation for the ion product of water.Kw = H+OH- = 10-146. If the pH of a solution is 7.8, what is the pOH? H+ =10-7.8= 1.58 x 10-8 (1.58 x 10-8)OH- =10-14OH- = 6.3 x10-7pOH= logOH-pOH = 6.27. Calculate the pKa of lactic acid, given that when the concentration of free lactic acid is 0.01M and the concentration of lactate is 0.087M, the pH is 4.80.pH = pKa + log (base/acid)4.80-log(0.087/0.01) = pKa4.80 0.9395 = 3.86pKa = 3.868. Calculate the pH of a mixture of 0.1 M acetic acid and 0.2 M sodium acetate. The pKa ofacetic acid is 4.75.pH = 4.75 + log (0.2/0.1)pH= 4.75 + 0.301pH =5.059. Calculate the ratio of the concentrations of acetate and acetic acid required in a buffer systemof pH 5.30.5.30 =4.75 + log(base/acid)0.55 = log (base/acid)100.55 = 3.55 ratio of base (acetate) to acid (acetic acid)10. If plasma arterial blood has a pH of 7.4 when equilibrated with CO2 at a pCO2 of 36 mmHg,what is the bicarbonate concentration in this arterial blood? 7.4 = 6.1 + log(HCO3/(S x PCO2)1.3 = log(HCO3/(0.03 x 36)101.3 = 19.95 = (HCO3/(1.08)21.546 = HCO311. The pK of phosphoric acid, H2PO4- in plasma is 6.8 at 37oC. At the normal pH of 7.4 of plasma, what is the molar ratio of HPO4= to H2PO4-?7.4 = 6.8 + log (HPO4/H2PO4-)100.6 = (HPO4/H2PO4-)= 3.9812. Most endotherms can tolerate deviations in their pH of no more than 0.5 units. If the normalpH is 7.4, what is the range of H in the body fluids of these animals in nanomoles?Range would be 6.9-7.96.9 = -logH+10-6.9=1.26 x 10-7M7.9 = -logH+10-7.9=1.26 x10-8Mnanomoles = 1x 10-9M1.26 x10-7M x 1nM/1 x10-9M=126 nM1.26 x 10-8M x 1nM/1 x 10-9M =12.6nM so from 12.6 nM to 126 nM13. If pH changes from 7.7 to 7.4 in one liter of solution, how many more hydrogen ions arepresent in the solution?10-7.4 = 3.98 x 10-810-7.7 = 2.00 x 10-8 Mso difference is 1.98 x 10-8Muse Avogadros number 6.022 x 10231.98 x 10-8M(6.022 x 1023atoms/M) = 1.19 x 101614. What is acid-base regulation? How does this concept relate to homeostasis?Maintaining a constant pH is an integral part of maintaining homeostasis because it ensures that the cells live in a fairly constant internal environment. We ingest and excrete various ions and these in addition to the use of buffers are utilized to keep the pH constant.15. If the pH of plasma is 7.4, what is the hydrogen ion concentration of plasma?Actually, I didnt catch that this is the same question as #4, so answer is H+ = 3.98 x 10-8 mol/L16. About 75% of the buffering of blood plasma is mediated by bicarbonate buffer. How does this buffer system work?The acid/base part of the reaction (H3O+ HCO3- H2CO3 + H20) works to prevent the formation of H30+ (hydronium) and OH- (hydroxide ions) which drive changes in pH. If an acid is added, the bicarbonate ion (HCO3-) acts as a base, pulling in hydrogen and preventing the formation of hydronium ions. If the fluid becomes basic, the carbonic acid (H2CO3) will act as proton donor and will prevent formation of hydroxide ions. Therefore, this buffer system will confer some resistance to changes in pH.17. The pKa of glycine, an amino acid, is 2.34. Do you think that glycine will serve as aneffective buffer in plasma?This pKa is not near the normal pH of the plasma which is a necessary trait for it to serve as an effective buffer. Glycine will not effectively resist the addition of strong acid.18. Suppose that you place animal in a chamber that contains more CO2 than normal. We notethat alveolar CO2 increases from 5% to 8% (assume that you are at sea level and thereforebarometric pressure = 760 mmHg). What will the new alveolar pCO2 be? How much will pHchange in this animal assuming that initial pH was 7.4. Partial pressure at 8% = 760 mmHg x 0.08= 60.08 mmHgI think I need another variable to be able to do this easily (pH or HCO3-)Im not sure19. Calculate at pH 7.4, what the bicarbonate concentration is at pCO2 of 20, 40 and 60 mmHg. Now draw a graph with bicarbonate concentration on the Y axis and pCO2 on the X axis. Whatdoes this graph tell you?7.4 = 6.1 + log(HCO3-/(S*PCO2)Different pressures of CO2 20*0.03 = 0.640*0.03 = 1.260*0.03 = 1.8Solve for each pressure:20: 11.9740: 23.9460: 35.91These values will give a linear graph so the bicarbonate concentration is positively and linearly correlated with pCO2Questions from Book1. What is the difference in extracellular, intracellular, and interstitial fluid?Intracellular: the areas of the body enclosed by cellsExtracellular: areas of the body not enclosed by cellsInterstitial fluid: the extracellular fluids other than blood plasma2. What is ionic regulation of blood plasma? How is volume regulation related to ionic regulation of blood plasma?Ionic regulation: the maintenance of a constant of nearly constant concentration of a particular ion in the blood. This is important for volume regulation because animals can control the direction of osmosis of water by controlling the concentrations of ions. Water is the main chemical involved in volume regulation in animals. If the animal makes the blood more concentrated for a particular ion, water will passively flow into the blood thereby increasing the volume of water in the blood.3. Would the osmolality of 1 g of NaCl in one liter of solution differ from the osmolality of 1 g of CaCl2 in one liter solution?Defintion of osmolality: number of osmoles (individual ions) of solute per liter of solution. Therefore these would not be the same for two reasons. One is that NaCl and CaCl2 have diffent molecular weights so 1g of each will provide different amounts of moles of the material.But even if we added a mole of each they would still be different because calcium chloride disassociates into 3 ions while sodium chloride disassociates into 2 which means that CaCl2 would have a higher osmolality.4. Suppose the barometric pressure is 760 mmHg and that the atmosphere is 10% water vapor. What is the water vapor pressure in this air?Partial pressure of water vapor =0.10.1 x 760 mmHg = 76 mmHg5. Now suppose that barometric pressure is 760 mmHg and that the relative humidity is 50%. What is the water vapor pressure of this air?For relative humidity, need to know the maximal partial pressure that water vapor can have at the same temperature. We dont have the temp here so you cant answer this.6. What is the difference between absolute humidity and relative humidity?Absolute humidity is simply the quantity of water vapor in a mass of air. You do not need temperature to calculate this.Relative humidity is the ratio of the partial pressure of water vapor to the saturated vapor of water at a given temperature. Therefore it tells you how close or far away from saturation the volume of air is. 7. Suppose a kangaroo rat oxidizes 4 grams o