Manual for laboratory classes in biological physics. Коллектив авторов
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 up to 14 % of its weight. In second place is the carbonate system in the third – a phosphate buffer system.
Of course, each buffer system may be kept constant pH within certain limits, which depend on its buffer capacity. Under the buffering capacity to understand the amount of 0.1N acid or alkali which is needed to shift the pH unit. An alkaline buffer is contained in the serum is about 5 times more than the acid, i.e. the acid can be neutralized to 5 times greater than the alkali. This means that the body is better protected from disturbances in blood entering the acidic products.
Laboratory work № 5
Definition of alkaline and acid buffers of serum blood
Objective: Buffer properties of serum
Tasks:
1. Carry out calibration of the device on standard solutions.
2. Measure рН of blood
4. Draw graphs of pH values
5. Make conclusions on the observed phenomena and do the report.
Equipment and Materials: pH-meter burette 1 and 50 ml, 50 ml cups, 0.1N solutions of hydrochloric acid and potassium hydroxide or sodium, 0.02 % methyl orange solution, 0.1 % ethyl alcohol solution phenolphthalein, serum.
Task 1. Acid buffer.
Procedure. Pour into a glass 5 ml of the distilled water and add 2-3 drops of methyl orange indicator, which has a transition zone pH = 3,1-4,4. Titrate drop by drop from a burette 0.1 N hydrochloric acid solution until a slight red coloration (1 drop of acid).
Pour into another glass 5 ml of the distilled water, add 1 ml of serum and 2-3 drops of methyl orange and titrated to the same stain; count the number of drops, or determine the amount of 0.1N hydrochloric acid solution that spent to the titration.
Calculation: for acidification 5 ml of water was spent A ml of 0.1 N hydrochloric acid (1 drop – 0.03 ml of 0.1N hydrochloric acid or alkali). By adding 1 ml of serum was spent B ml of hydrochloric acid. Thus, for 5 ml serum would be spent: (B-A × 5ml 0.1N Hydrochloric acid). In the calculations of the buffer capacity of the water can be ignored. Make a calculation for 100 ml of serum, which would be its buffer capacity. The results bring to the table 3.4.1.
Normally, for serum it is necessary to add 250-300 times more hydrochloric acid than for water.
Task 2. Alkaline buffer.
Procedure.
Pour into a glass 10 ml of the distilled water and add 2-3 drops of a phenolphthalein; transition zone pH =8,9-9,8. To titrate 0,1 N solution of caustic sodium before appearing weak-violet coloring (usually 1-2 drops).
In the second glass to pour 10 ml a dist. waters to add 1 ml of serum and 2-3 drops of a phenolphthalein. To titrate 0,1 N solution of caustic sodium before the same coloring, as in the first case, counting quantity of drops or measuring volume. Write the results in table 3.4.1.
Table 3.4.1
Acidic and alkaline buffers serum