## Oh

It is absorbed into the blood through the cells lining the stomach and the small intestine. Absorption requires passage through the plasma membrane, the rate of which is determined by the polarity of the molecule: charged and highly polar molecules pass slowly, whereas neutral hydrophobic ones pass rapidly. The pH of the stomach contents is about 1.5, and the pH of the contents of the small intestine is about 6. Is more aspirin absorbed into the bloodstream from the stomach or from the small intestine? Clearly justify your choice.

9. Preparation of Standard Buffer for Calibration of a pH Meter The glass electrode used in commercial pH meters gives an electrical response proportional to the concentration of hydrogen ion. To convert these responses into pH, glass electrodes must be calibrated against standard solutions of known H+ concentration. Determine the weight in grams of sodium dihydrogen phosphate (NaH2PO4 • H2O; FW 138.01) and disodium hydrogen phosphate (Na2HPO4; FW 141.98) needed to prepare 1 L of a standard buffer at pH 7.00 with a total phosphate concentration of 0.100 M (see Fig. 2-16).

10. Calculating pH from Hydrogen Ion Concentration

What is the pH of a solution that has an H+ concentration of

(a) 1.75 X 10-5 mol/L; (b) 6.50 X 10-10mol/L; (c) 1.0 X 10-4 mol/L; (d) 1.50 X 10-5 mol/L?

11. Calculating Hydrogen Ion Concentration from pH

What is the H+ concentration of a solution with pH of (a) 3.82;

12. Calculating pH from Molar Ratios Calculate the pH of a dilute solution that contains a molar ratio of potassium acetate to acetic acid (pKa = 4.76) of (a) 2:1; (b) 1:3; (c) 5:1; (d) 1:1; (e) 1:10.

13. Working with Buffers A buffer contains 0.010 mol of lactic acid (pKa = 3.86) and 0.050 mol of sodium lactate per liter. (a) Calculate the pH of the buffer. (b) Calculate the change in pH when 5 mL of 0.5 m HCl is added to 1 L of the buffer. (c) What pH change would you expect if you added the same quantity of HCl to 1 L of pure water?

14. Calculating pH from Concentrations What is the pH of a solution containing 0.12 mol/L of NH4Cl and 0.03 mol/L of NaOH (pKa of NHj/NH3 is 9.25)?

15. Calculating p^a An unknown compound, X, is thought to have a carboxyl group with a pKa of 2.0 and another ionizable group with a pKa between 5 and 8. When 75 mL of 0.1 m NaOH was added to 100 mL of a 0.1 m solution of X at pH 2.0, the pH increased to 6.72. Calculate the pKa of the second ionizable group of X.

### 16. Control of Blood pH by Respiration Rate

(a) The partial pressure of CO2 in the lungs can be varied rapidly by the rate and depth of breathing. For example, a common remedy to alleviate hiccups is to increase the concentration of CO2 in the lungs. This can be achieved by holding one's breath, by very slow and shallow breathing (hypoventilation), or by breathing in and out of a paper bag. Under such conditions, the partial pressure of CO2 in the air space of the lungs rises above normal. Qualitatively explain the effect of these procedures on the blood pH.

(b) A common practice of competitive short-distance runners is to breathe rapidly and deeply (hyperventilate) for about half a minute to remove CO2 from their lungs just before running in, say, a 100 m dash. Blood pH may rise to 7.60. Explain why the blood pH increases.

(c) During a short-distance run the muscles produce a large amount of lactic acid (CH3CH(OH)COOH, Ka = 1.38 X 10~4) from their glucose stores. In view of this fact, why might hyperventilation before a dash be useful?

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### Responses

• toini reinikainen
What is the ph of a solution containing 0.12 m of nh4cl and 0.03 mol/l of?
7 years ago