of chloride potassium continuously filters through glass fiber of a stopper, preventing penetration from controlled solution into system of an electrode of 4 foreign ions which could change electrode potential size.
The electromotive force of the electrode system is equal to the algebraic sum of the potentials of the contact electrodes Ec and Eaux, potential occurring on the inner surface of the glass electrode and a defined pH internal solution Eint and potential arising on the outer surface of the glass electrode Ec. The values Ec,,Eaux and Eint does not depend on the composition of the control solution and only change when the temperature changes. The total electromotive force of the electrode depends linearly on the pH of the solution. By measuring the emf an electrode system with an electronic millivoltmeter 7, a scale which is graduated in units of pH, determine the pH-controlled solution.
Laboratory work № 3
pH of various solutions and biological liquids
Objective: Experimentally find pH values of various solutions and biological liquids.
Tasks:
1. Calibrate the device on standard solutions.
2 Measure рН of various solutions and biological liquids.
3. Draw graphs of pH values of various solutions, and biological and non-biological liquids.
4. Make conclusions about the observed phenomena and prepare a report.
Equipment and Materials: pH meter, nitric acid, alkali, solutions of proteins, gastric juice, urine, distilled water, vessels.
Procedure:
Rinse thoroughly with electrodes; the purity of the electrodes is judged by the pH of distilled water. Electrodes may be used for research in case, if pH value of distilled water close to 6,0-6,3.
Determine pH value of the following solutions: gastric juice diluted (5-fold) gastric juice protein solution, an acidic solution, an alkaline solution, tap water, distilled water. Measuring the pH of the sample solution should be performed at least in triplicate. Before replacing of the sample solution the electrodes should be thoroughly washed. Record these pH values in the table 2.3.1.
Table 2.3.1
Based on these data, you must specify what determines the specific pH of each solution.
Report design. The results bring to the table and to construct graphics (histograms). Define measurement error and to draw conclusions.
`Laboratory work № 4
Determination of pH of fermented milk products using a pH meter
Objective: pH of various solutions and of biological fluids.
Tasks:
1. Perform calibration standard solutions.
2. To measure the pH of various solutions and biological fluids.
4. Build a graphic pH of various solutions, and biological and non-biological fluids.
5. Make conclusions about the observed phenomena and prepare a report.
Equipment and materials: pH meter burette 1 and 50 ml, 8-10 cups 50 ml of 0.01N. sulfuric acid, distilled. water, yogurt (or any other dairy products)
Task 1. Determination pH of the solution with sulfuric acid of various concentrations
Procedure: you need to determine the pH of 0.01 n. sulfuric acid solution. Then prepare a dilution at two, four and eight times, and carry out measurements. Plot the pH of the test solution concentration.
Task 2. Determination pH of fermented milk products with different concentrations
Procedure: Measure the pH of the original dairy products. Then prepare a dilution at two, four and eight times, ten times, and carry out measurements. Plot the pH of the test solution concentration.
To explain the observed differences in the results and graphs.
Table 4.1.1
pH values
Chapter 2 «Physical-chemical methods» questions:
1. What is the pH of solutions and how to determine its value?
2. Why does the pH change?
3. What instruments allow us to estimate the pH
4. How big limits could change pH in living objects?
5. Explain, how ph-meter measure pH value.
6. What substances are buffering?
7. Describe the dissociation of the peptide.
8. Describe the dissociation of sulfuric acid, for some reason it does not have buffer properties?
9. Explain biological significance for constancy of pH within each cell, and in all body fluids.
10. Why diluted fermented milk product solution’s pH does not change much, while a dilution of sulfuric acid (or salt) in 10 times pH changes a lot?
Chapter 3
BUFFER PROPERTIES AND BUFFER CAPACITY OF BIOLOGICAL LIQUIDS
The constancy of the hydrogen ion concentration of blood and other body fluids is provided by a number of mechanisms. Despite the many processes that result can change the internal environment of the reaction, the pH is constant. In warm-blooded animals, constancy of pH of the internal environment is maintained during the life of a very narrow range, the deviation does not exceed 0,03-0,04 units. (in human blood pH is 7,35±0,02).
The shift reaction medium leads to a change in many physical and chemical indicators of protein nuclein, and protein lipid complexes – the magnitude of the charges, the extent of hydration, stability of colloids, viscosity, electrical conductivity, etc. Changes in biochemical reactions lead to disruption of conjugation of many biochemical processes that may be the cause of death of the organism.
However, in a normally functioning blood in the living body continuously it receives the acid products of working organs and the gastrointestinal tract. Alkaline reaction products enter the body mainly in food. To maintain a constant internal environment include buffers which neutralize both the acid and alkali in the received blood products stably maintain the reaction medium (hydrogen ion concentration) at a predetermined level. Buffer systems are presented with proteins or systems consisting of a weak acid and a strong base salt of this acid (Н2СО3 and NaHCO3; H3PO4 and Na2HPO4; H3PO4 and Na3PO4 etc.).
The main role of proteins in the body member which are amphoteric compounds, and proteins from the blood hemoglobin plays a specific role, in which human blood contains
