Karaganda State Medical University. Chemistry department. Lecture on the topic:Lecture on the topic: The doctrine of the solutions. Buffered solutions. For the 1st year students of specialty “General medicine". Discipline: Chemistry. Lecturer: PhD, Associate Professor Vlassova Lenina. Karaganda 2014

Primary goal. The aim of the first lecture is the solution of the problem of the constancy of the medium in the body, what factors affect on the acid-base balance and homeostasis.

objectives: As a result of studying the topic, you should: 1. Be able to define and know the classification of solutions. 2. Be able to distinguish between acids and bases. 3. Be able to define reaction of water and the pH of the medium. 4. Buffers is necessary to understand as a factor in maintenance of a constancy the medium in the body.

Definition and classification of solutions. The processes assimilation of food and excretion metabolic products from the body of a living organism are directly linked with the solutions. The processes of digestion and assimilation of food begins with transfer of nutrients in solutions. The blood plasma, lymph, saliva, urine, intracellular fluid, gastric juice and other body fluids are solutions. The most drugs as a solutions is introduced into the body.

The blood.

Urine of healthy human.

The solutions are called the homogeneous system consisting of solute, solvent and products of their interaction. The solutions are divided into three groups of aggregation state : 1) gas solutions (air) 2) solid solutions (alloys, glass) 3) liquid solutions (solutions of acids, bases, sugars, etc.)

Composition of air.

Bronze alloy with other metals.

liquid solutions.

large -dispersion: a particle size greater than 10-7m (suspensions, emulsions).

Colloids.

Molecular (the true) solutions.

The solutions are classified into solutions: - Non-electrolytes, - electrolytes - Polyelectrolytes. Polyelectrolytes are called high-molecular compounds containing ionogenic groups. In aqueous solution, they have the properties of electrolytes. The most important representatives of this group of natural substances are proteins.

The concept of acids and bases. In order to understand the mechanism of acid-base reactions in the body, we must learn what the acid and base. For this purpose two basic theory of acids and bases applied.. 1. The S.Arennius theory of electrolytic dissociation : According to that: Acid - the electrolytes, forming in the dissociation of hydrogen cations (H + ); Base- the electrolytes, which form in the dissociation of the hydroxyl anion (OH-).

Base- the electrolytes, which form in the dissociation of the hydroxyl anion (OH-). Acid - the electrolytes, forming in the dissociation of hydrogen cations (H +);

The diagram shows the dissociation process Initially, the crystal salt is surrounded by molecules (dipoles) of water. Next, there is the formation of solvation shells around the ions of sodium and chlorine. Next, sodium and chlorine ions free are present in solution through a process of solvation.

As a result of the recoil and adoption of proton,acides and bases form conjugate acid-base pairs. Protolytic (proton) theory of Bronsted – Lowry. Acids - the donors of protons (H +) Bases - acceptors of protons (H +). As a result of the recoil and adoption of proton,acides and bases form conjugate acid-base pairs.

Conjugate Acid-Bases and Their Relative Strengths Conjugate Acid Conjugate Base NameFormula Name Perchloric acidHClO 4 ClO 4 - Perchlorate Ion Sulfuric AcidH 2 SO 4 HSO 4 - Hydrogen Sulfate or Bisulfate Ion Hydrogen ChlorideHClCl - Chloride Ion Nitric AcidHNO 3 NO 3 - Nitrate Ion Hydronium IonH3O+H3O+ H2OH2OWater Hydrogen Sulfate or Bisulfate Ion H 2 SO 4 SO 4 = Sulfate Ion

In pure water: [H+] = [OH-] = mol/l - neutral medium if [H+] > [OH-], that [H+] > mol/l - acidic medium if [H+] < [OH-], that [H+] < mol/l - alkaline medium.

Hydrogen index is introduced for the convenience the estimation of the acidity and basicity. The pH - is the negative logarithm of hydrogen ion concentration : рН = - log [H + ] Is also used hydroxyl index - the negative logarithm of concentration of hydroxyl groups: рОН = - log [OH - ] The ion- product constant of water is often expressed in logarithmic form: рН + рОН = 14

If рН = 7, рОН = 7 – neutral medium рН > 7 рОН 7 – acidic medium (0-3 - strongly acidic (gastric juice), weakly acidic, weakly alkaline, strong basic)

By its strength acids and bases are strong and weak. For weak acids, the pH is by the formula: рН = ½ рК a - ½ lg C a, where рК = - lgК called the index of the dissociation constant of a weak acid or base, C - concentration of the solution. For weak bases the pH is given by : рН = 14 - ½ рК b + ½ lg C b

For strong acids the pH is by the formula: рН = - lg (zC a ), wherein z - the number of hydrogen ions For strong bases pH is given by: рН = 14 + lg (zC b ). where z - the number of of hydroxyl ions

The buffered systems of the body and their classification. In maintaining the constancy of the active medium reaction of the organism are important buffers. Buffers or solutions - are solutions that have the ability to maintain the pH at a constant level by adding small amounts of acids or bases or at a dilution.

Calculation of pH buffered systems. Each of the buffer systems characterized by a defined the active medium reaction, determined the basic equation of buffered systems. Calculation of acidity for acid buffered systems: [H+] = Ka Ca Cs The calculation of the basic medium for the basic buffered systems: [OH-] = Kb Cb Сs where: Ka and Kb - dissociation constants of weak acids and bases, Ca, Cb, Cs - concentration of acids, bases and salts.

The calculation of pH buffered systems implemented by the Henderson - Gasselbah equations for acid buffered systems: pH = pKa – lg Ca Cs For the basic buffered systems: pH = 14 – pKb + lg Cb Cs From the equation one can see that depends on the acidity of the buffered systems: 1. the nature of the weak electrolyte, or, its dissociation constant. 2. the ratio of the components of the buffer system

The buffer capacity. The ability of buffered systems to retain pH at a certain level is limited. The ability of the buffered system to counteract pH change is determined by the buffer capacity. The buffer capacity is equal to the number of strong acid or base, which when adding to 1 liter of the buffer solution thus the pH will change by one unit. B = CV ∆pH∙W where, C and V - concentration and volume of strong acid or base ; ΔpH - pH change, W - volume of buffered solution

The buffered systems of the body Of the buffered systems of the body most interest are the following: - hemoglobin- oxyhemoglobin (HHb/HhbO 2 ), - bicarbonate (H 2 CO 3 /NaHCO 3 ), - phosphatic (NaH 2 PO 4 /Na 2 HPO 4 ) - proteinaceous (NH R – COO - ). Each of them plays a role in the regulation of acid-base equilibrium, while buffered systems are operated instantaneously.

pH blood is 7.4. The shift of the pH blood in the acidic area (acidosis) or alkaline (alkalosis) is regulated by bicarbonate buffer with the participation of the respiratory system by regulating the concentration of CO 2 in the blood. Changes in the concentrations of components of buffer systems of the body is regulated by bodies selection (kidneys, sweat and salivary glands, intestines, etc.).

The possible states of the organism

Thank you for your attention.