174 ACIDITY 



Table 7-3 



pH values of representative biological materials 



Matenal pH Value 



Blood, normal limits 7.3-7.5 



Blood, extreme limits 7.0-7.8 



Enzymes, activity range of 



Amylopsin, optimum 7.0 



Erepsin, optimum 7.8 



Invertase, optimum 5.5 



Lipase, pancreatic 7.0-8.0 



Malta.se, optimum 6.1-6.8 



Pepsin, optimum 1 .5-2.4 



Trypsin, optimum 8-9 



Fruit juices 



Apple 3.8 



Banana 4.6 



Grapefruit 3.0-3.3 



Orange 3.1-4.1 



Tomato ^' 4.2 



Ga.stric juice, adult 1.6-1.8 



Milk, cows, limits 6.2-7.3 



Milk, human 7.0-7.2 



Muscle juice : 6.8 



Plants (extracted juice) 



Alfalfa tops 5.9 



Carrot 5.2 



Cucumber 5.1 



Peas, field 6.8 



Potato 6.1 



Rhubarb; stalks 3.4 



String beans 5.2 



Saliva 6.2-7.6 



Sweat 4.5-7.1 



Tears : 7.2 



Urine, human, limits* 4.2-8.0 



REVIEW QUESTIONS ON ACIDITY 



1. Explain the difference in meaning of "active" and "total" acidity. In what 

 terms are concentrations of the two usually expressed? 



2. Define: (1) molar solution, (2) normal solution,^ (3) hydrogen equivalent, (4) 

 gram equivalent weight, (5) indicator. 



3. What is the normality of a solution of NaOH if 25 ml. of it are required to 

 neutralize 20 ml. of O.IA'^ oxalic acid? 



4. What is the normality of a solution of acetic acid which contains 0.3 g. of this 

 reagent in 50 ml.? 



5. What volume of 0.5iV NaOH would be required to neutralize the acetic acid 

 mentioned in the preceding question? 



6. What is a hydrogen ion? Represent by equations the ionization of (1) HNO3, 

 (2) NaCl, (3) ClicHOHCOOH, (4) NaOH, (5) H2SO.. 



