Methodical instruction for students of the I course

Methodical instructions for the 1^st year students

Dental faculty

 

LESSON 6 (6 HOURS)

THEMES:

1. Disperse systems. Colloidal solutions and their properties. Preparation and purification of colloidal solutions. Electrophoresis. Electroosmosis.

2. Coagulation of sol by electrolytes. Determination of coagulation threshold.

3. Macromolecular compounds (MMC): properties, protective effect on colloidal solutions. Swelling and dissolution of polymers.

 

AIM:

To study the methods of preparation and purification of colloidal solutions, their properties and application in clinical and pharmaceutical practice. To study coagulation mechanism and factors that cause coagulation. Determine coagulation thresholds. Understand the mechanism of protective action of macromolecular compounds. To study the effect of electrolytes and pH on the degree of macromolecular compounds swelling.

 

PROFESSIONAL ORIENTATION OF STUDENTS:

A living organism can be viewed as a complex combination of disperse systems. Cells, blood cells, bacteria form coarse dispersion systems. Lipids, proteins, polysaccharides, nucleic acids form colloidal solutions. Change of the physical-chemical state of dispersion systems in the organism can lead to pathologies. Blood coagulation, transport of lipids and water-insoluble compounds, formation of cholesterol plagues in the blood vessels and other important processes are based on the properties of dispersion systems. Research of dispersion systems has introduced such modern diagnostics and treatment as electrophoresis, compensatory dialysis, vividialysis, “artificial kidney”.

Stability of biological dispersed systems depends on constancy of pH, electrolyte and protein composition. Their change can lead to coagulation of the colloidal phase, sedimentation of erythrocytes and proteins. Coagulation takes place in blood clotting.

Colloidal protection is of great importance for the normal functioning of the organism. Proteins, polysaccharides and other natural polymers are adsorbed on the surface of colloidal hydrophobic particles, thus increasing their hydrophylity. The polymers promote stability of the particles because they protect them form coagulating action of electrolytes. Particles of lipids, cholesterol, insoluble calcium phosphates, urates and oxalates exist in the body fluids in the protected state.

 

BASIC LEVEL

1. Exchange reactions, concept of salts hydrolysis (secondary school course in chemistry).

2. Dissociation of electrolyte (secondary school course in chemistry).

3. Macromolecular compounds and their structure (secondary school course in chemistry).

 

STUDENTS’ SELF-PREPARATION PROGRAM.

Theme 1. Disperse systems. Colloidal solutions and their properties. Preparation and purification of colloidal solutions. Electrophoresis. Electroosmosis.

1. Disperse systems. Classification of disperse systems by the aggregative state and the size of dispersed phase particles. Lyophilic and lyophobic colloidal solutions.

2. Preparation of colloidal solutions by condensation and dispergation methods.

3. Purification of colloidal solutions: dialysis, electrodialysis, compensatory dialysis, vividialisis, hemodialysis. “Artificial kidney”.

4. Structure of micelle, as a base unit of colloidal solution.

5. Molecular-kinetic properties of colloidal solutions (Brownian motion, diffusion, osmosis).

6. Optical properties of colloidal solutions. Tyndall effect.

7. Electrical properties of colloidal solutions. Electrokinetic potential.

8. Electrophoresis and electroosmosis. Application of electrophoresis in medical and biological researches.

Theme 2. Coagulation of sol by electrolytes. Determination of coagulation threshold.

1. Stability of colloidal solutions. Factors of sols stability.

2. Coagulation. Causes and mechanism of coagulation. Coagulation by electrolyte. Schulze–Hardy rule. Coagulation threshold.

3. Kinetics of coagulation.

4. Coagulation in biological systems.

Theme 3. Macromolecular compounds (MMC): properties, protective effect on colloidal solutions. Swelling and dissolution of polymers.

1. Macromolecular compounds, their structure and obtaining.

2. Biological macromolecular compounds (biopolymers).

3. Formation and characteristics of solutions of macromolecular compounds.

4. Colloidal protection. Protective number. Biological importance and application of colloidal protection.

5. Swelling and dissolution of polymers. Degree of swelling.

6. Effect of temperature, pH and electrolyte on the swelling of macromolecular compounds.

 

METHODOLOGY OF PRACTICAL CLASS (9⁰⁰-12⁰⁰)

Theme 1. Disperse systems. Colloidal solutions and their properties. Preparation and purification of colloidal solutions. Electrophoresis. Electroosmosis.

 

Work 1. Obtaining of an iron hydroxide sol by the method of hydrolysis

Materials: 5 % FeCl₃ solution, distilled water, conical flask

Protocol. Add 50 ml of distilled water to a conical flask and boil it. Measure out 5 ml of 5 % FeCl₃ (with a measuring test tube) and add it gradually to the boiling water. A clear reddish-brown sol is obtained.

At high temperature complete hydrolysis of iron (III) chloride occurs:

The products of the hydrolysis partially react with each other:

The obtained iron oxychloride (FeOCl) stabilizes colloidal particles.

Write the structure of micelle of Fe(OH)₃ sol.

 

Work 2. Purification of iron hydroxide sol by the dialysis method

Materials: iron hydroxide sol, funnel with a cellophane film, beaker, 5% AgNO₃ solution

Explain the principle of dialysis.

 

Work 3. Obtaining of a silver iodide sol by the double exchange reaction

Materials: 0,002 mol/l KI solution, 0,01 mol/l AgNO₃ solution

Protocol. a) With an excess of potassium iodide. Add 10 ml of KI solution and 1 ml of AgNO₃ solution to the test tube.

b) With an excess of a silver nitrate. Add 5 ml of KI solution and 2 ml of AgNO₃ solution to the test tube.

A light yellow colloidal solution of silver iodide is obtained in two test tubes. Write an equation of the reaction and structure of micelle of the silver iodide sol.

 

Work 4. Obtaining of a Prussian blue sol by the double exchange reaction

Materials: 2% FeCl₃ solution, 0,01 % K₄[Fe(CN)₆] solution

Protocol. a) With an excess of a potassium hexacyanoferrate (K₄[Fe(CN)₆]). Add 10 ml of K₄[Fe(CN)₆] solution and 2 drops of FeCl₃ solution to the test tube.

b) With an excess of a iron (III) chloride. Add 10 ml of FeCl₃ solution and 2 ml of K₄[Fe(CN)₆] solution to the test tube.

A clear blue colloidal solution of Prussian blue Fe₄[Fe(CN)₆]₃ is obtained. Write an equation of the reaction.

 

Work 5. Obtaining of phenolphthalein hydrosol by exchange of solvent

Materials: 0,5% phenolphthalein alcohol solution

Protocol.: Colloidal solution of certain substances, which are soluble in alcohol but insoluble in water can be prepared by pouring their alcoholic solution in excess of water.

Add 1 ml of distilled water and some drops of phenolphthalein alcohol solution to the test tube. Alcohol solution of phenolphthalein when pouring into water gives milky colloidal solution of phenolphthalein.

 

Work 6. Determination of the sign of sols charge and dyes particles by method of capillarity.

Materials: Filter paper, iron hydroxide sol, konho red solution, methyl blue solution, fuchsine aqueous solution, eosine solution

Protocol. Determination of the sign of colloidal particles charge is based on the fact that some substances, such as paper, silk, glass, sand, etc., when immersed in water are negatively charged. If the colloidal particles in solution are negatively charged, they are repelled from the filter paper and flowed with water. If the sign of colloidal particles charge is positive, it is attracted to paper and is left in the center of the drop.

Drop a little of solution on filter paper: iron hydroxide sol, konho red solution, methyl blue solution, fuchsine aqueous solution, eosine solution. After some time you can watch different shapes and sizes of spots. Record sign of colloidal particles charge of each solution.

 

Theme 2. Coagulation of sol by electrolytes. Determination of coagulation threshold.

Work 7. To study coagulation of iron (III) hydroxide sol by the action of electrolytes

Materials: Fe(OH)₃ sol, 3 mol/l KCl solution, 0,01 mol/l K₂SO₄ solution, 0,001 mol/l K₃[Fe(CN)₆] solution.

Protocol.

Take 12 test tubes and place them in three rows (4 tubes in each row). Add 5 ml of Fe(OH)₃ sol to each tube. Add distilled water and KC1 solution as it is shown in the Table 1 to the test tubes of the first row. Add water and K₂SO₄ solution to the test tubes of the second row. Add water and K₃[Fe (CN)₆] solution to the test tubes of the third row.

Mix the solutions in each test tube and leave for one hour.

Table 1

 

After 1 hour, look at each test tube and observe coagulation (turbidity) or sedimentation (precipitation). Record the results in the Table 2.

Table 2

Calculate coagulation threshold for all electrolytes by the formula:

Where:        C_el – molar concentration of the electrolyte, mol/l

V_el – minimum volume (ml) of electrolyte, which causes coagulation

V_sol – volume of sol (ml)

The inverse value to the coagulation threshold is called coagulation power and expressed as 1/C_threshold.

Record the results in the Table 3:

 

Theme 3. Macromolecular compounds (MMC): properties, protective effect on colloidal solutions. Swelling and dissolution of polymers.

 

Work 8. To study the colloidal protection of solutions of macromolecular compounds

Materials: Fe(OH)₃ sol, 0,5 % gelatine solution, 0,5 % starch solution, 0,5 % egg albumin solution, 0,15 mol/l K₂SO₄ solution, burette.

Protocol. Add 5 ml of Fe(OH)₃ sol to 4 test tubes. Pour 1 ml of 0,5% gelatine solution to the second test tube; 1 ml of 0,5% starch solution– to the third; 1 ml of 0,5% egg albumin solution – to the fourth. After that the solutions in each test tube must be titrated with 0,15 mol/l K₂SO₄ solution to the coagulation (slight clouding) appearance.

Record the results in the table.

Make a conclusion about colloidal protection of solutions of macromolecular compounds.

 

Work 9. To study the effect of pH on the swelling of polymers

Materials: dry gelatine, 0,1 mol/l НСl solution, 0,1 mol/l NaOH solution, 0,5 mol/l СН₃СООН solution, 0,5 mol/l СН₃СООNа solution

Protocol. Add 0,5 g of dry gelatine to the three dry measuring test tubes.

Add 8 ml of 0,1 mol/l НСl to the first test tube;

Add 8 ml of 0,1 mol/l NaOH to the second test tube;

Add 4 ml of 0,5 mol/l СН₃СООН (К_d = 1.75 · 10^-5) and 4 ml of 0,5 mol/l СН₃СООNа to the third test tube. pH of the solutions that are added should be pre-measured. Mix the content of the tubes and leave for 1 hour (during this time the solutions should be mixed periodically). After 1 hour, measure the height swelling of gel. Explain the dependence of the degree of gelatine swelling on pH (pI gelatine = 4,7)

 

Work 10. To study heat release during swelling

Materials. dry starch, distilled water, flask, thermometer.

Protocol. Add 5 ml of distilled water to the flask and measure its temperature with thermometer. Add 5 g of dry starch. Measure the temperature of the mixture with the thermometer and. Explain the reasons for the temperature change.

 

SEMINAR DISCUSSION OF THEORETICAL ISSUES (12³⁰-14⁰⁰).

 

TEST EVALUATION AND SITUATIONAL TASKS.

Multiple choice tests

1. What type of the disperse system does fog belong to (G-gas, L-Liquid, S-solid):

A. G/S;

B. S/S;

C. L/L;

D. G/G;

E. L/G

2. Chose method of preparation of colloid solutions by this reaction 2Н₂S+SO₂ = 3S+2H₂O:

A. Peptization;

B. Oxidation;

C. Electric method;

D. Hydrolysis;

E. Double decomposition.

3. Which method can be used for colloidal solution purification?

A. Dialysis

B. Condensation   

C. Electrophoresis 

D. Sedimentation 

E. Titration

4. Choose the electrolyte with minimal coagulation threshold for sol with negatively charged particles:

A. Na₂SO₄

B. K₃PO₄

C. CaCl₂

D. Al(NO₃)₃

E. NH₄Cl

5. Which factor can cause such pathologies as atherosclerosis and kidney stones?

A. Decreasing of glucose level in the blood;

B. Decreasing of protective action of proteins in the organism;

C. Decreasing of salt content in the blood 

D. Increasing concentration of proteins in the organism;

E. Coagulation of blood cells

 

Examples of solving tasks

 

Task 1. To obtain barium sulfate sol 15 ml of 0,02 mol/l sodium sulfate solution and 100 ml of 0,005 mol/l barium chloride solution were added. Write a formula of micelle BaSO₄ sol.

Answer:

Equation of the reaction:

Sol is formed, as one of the reactants is taken in excess.

Calculate the number of moles of reactants

 ;

Thus, BaCl₂ is in excess and is stabilizer

The formula of micelle:

 

Task 2. Coagulation of 2 ml of AgI sol has occurred at addition of 0,4 ml BaCl2 with the molar concentration 0,05 mol/l. Calculate the coagulation threshold of this sol.

Answer:

 

Task 3. 3 ml of 0,5% dextrin aqueous solution (ρ = 1g/ml) were added to 5,5 ml of Al₂S₃ sol with negative charge of granule. Coagulation of this mixture has occurred at addition of 1,5 ml of NaCl solution with the molar concentration 2,5 mol/l. Calculate the protective number and coagulation threshold of this sol.

Answer:

 

Task 4. Piece of natural rubber with the volume of 1,094·10^{–4 m3} was placed in carbon disulfide. After 48 hours exposure at 298 K, volume of rubber was 9,204·10^{–4 m3} Calculate the degree of swelling of the polymer.

Answer:

 

 

Tasks

Task 5. The sol ZnS is obtained by mixing of equal volumes of the solutions (NH₄)₂S with the molar concentration 0,02 mol/l and ZnCl₂ with the molar concentration 0,005 mol/l. Write the formula of micelle ZnS sol.

Task 6. Write the formula of micelle of a sol, obtained by mixing of 15 ml of 0,025 mol/l KCl solution and 85 ml of 0,005 mol/l AgNO₃ solution.

Task 7. Coagulation of 10 ml of iron hydroxide hydrosol has occurred at addition of 2 ml of sodium sulfate with the molar concentration 0,025 mol/l. Calculate the coagulation threshold of this sol.

Task 8. Coagulation threshold of Na₂SO₄ for silver iodide hydrosol is 25 mmol/l. Coagulation of 250 ml of this sol has occurred at addition of 50 ml of sodium sulfate Calculate the concentration of electrolyte.

Task 9. To 20 ml of Prussian blue sol, 2 ml of 1 % gum arabic solution (ρ = 1g/ml) were added. Coagulation of this mixture has occurred after addition of 0,5 ml of 10 % NaCl solution. Calculate the protective number of gum arabic for this sol.

Task 10. 10 g of protein was placed in water. After some time mass of protein was 16 g. Calculate the degree of swelling of protein.

 

Students should know:

·       Dispersion systems and their classification;

·       Methods of obtaining and purification of colloidal solutions;

·       Structure of micelle;

·       Properties of colloidal solution;

·       Coagulation of colloidal solutions;

·       Colloidal protection;

·       Macromolecular compounds and properties of its solution.

 

Students should be able to:

·       Obtain colloidal solutions in the laboratory;

·       Purify colloidal solution;

·       Write the formula of micelle;

·       Determine and calculate coagulation threshold;

·       Determine the sign of sol particles charge by the method of capillarity;

·       Calculate the protective number of polymers;

·       Calculate the degree of swelling of macromolecular compounds.

 

Correct answers of test evaluations and situational tasks:

Multiple choice tests

1. E; 2. B; 3. A; 4. D; 5. B

Tasks

5

6.

7. 4,17 mmol/l

8. 0,15 mol/l

9. 40 mg

10. 60 %

 

References:

1. http://intranet.tdmu.edu.ua/ Student’s facilities /Lecture presentations /Department of General Chemistry/ English / dental /1 course/ medical chemistry/ 05. Disperse systems. Colloidal solutions

2. http://intranet.tdmu.edu.ua/ Student’s facilities /Practical classes materials /Department of General Chemistry/ medical chemistry/ dental/ 1 course/ English/ 06. Colloidal solutions. Coagulation. Macromolecular compounds

3. Atkins, Peter W.; de Paula, Julio. Physical Chemistry (9th ed.). Oxford University Press. – 2010. –  ISBN 978-0-19-954337-3.

4. Birdi, K. S. Surface and colloid chemistry: principles and applications / K.S. Birdi. Taylor and Francis Group, LLC – 2010. – ISBN 978-1-4200-9503-6.- p.141-161.

5. Physical Chemistry of Surfaces, by A. Adamson & A. Gast, 6th Ed. Wiley, 1997, ISBN-0-471-14873-3.

6. Ebbing D. D., Gammon S. D. General Chemistry. Ninth edition. Houghton Mifflin Company, Boston New York. –  2009. – ISBN-10: 0-618-85748-6

7. Monk, Paul M. S. Physical chemistry: understanding our chemical world / Paul Monk. Wiley, New York, 1994. – ISBN 0-471-49180-2.

8. Chemistry” 3th ed. J. Mc Murry and R. Fay; – Prentice Hall, Upper Saddle River, New Jersey 07458. – 2001. – ISBN 0-13-087205-9;

 

Methodical instructions have been worked out by:

Associate Prof. Kyryliv M. V.

 

 

Methodical instructions were discussed and adopted at the Department sitting

27 August 2013. Minute № 1