Solutions. Types of disperse systems. True solutions. Water as most widespread solvent in pharmacy. Solvatation and heat effect of solubility process. Solubility of solid, liquids and gases (Henry law).concentration units.

LECTURELECTURE 11

ass. prof.ass. prof. Ye. B. DmukhalskaYe. B. Dmukhalska

PLAN

1. Solubility. The mechanism of dissolving. 2. Solubility of gases in liquids. The Henry’s law. 3. Colligative properties:a) osmosis. The vant’-Hoff’s law. Hemolysis and

plasmolysis;b) vapor-pressure lowering of solution. A Raoult’s law;

c) boiling-point elevation;

d) freezing-point depression.

Water – main solvent

The water - main component of organisms and medium, in which lives the person. The main properties of water that in water can solubility a different matters.

In the human, animal, plant organisms the water is main part, a constituent solvent and it participates in exchange reactions of matters (hydrolysis, hydration, swelling, digestion).

In a human organism are about 70 - 80 % of water.

The mechanism of dissolving

(- +)Polar molecule

(-) Negative ion

(+) Positive ion

(-+)Water dipole

The dissolving depends primarily on the relative strengths of three attractive forces:

1) the forces between the particles of the solute before it has dissolved {solute-solute forces),

2) the forces between solvent particles before dissolution has taken place (solvent-solvent forces),

3) the forces that are formed between solute and solvent particles during the dissolving process (solute-solvent forces).

Type of solutionA saturated solution is one that is in equilibrium with excess

undissolved solute, or would be in equilibrium if excess solute were present. The term saturated denotes the highest concentration of solute which a solution can have and be in equilibrium with any undissolved solute with which it is placed in contact.

An unsaturated solution is one in which the concentration of solute is less than its concentration in a saturated solution.

A supersaturated solution is one in which the concentration of solute is greater than its concentration in a saturated solution.

A supersaturated solution is unstable and its solute tends eventually to crystallize out of solution, much as a super cooled liquid tends eventually to crystallize.

• Gas solution is not possible to prepare a heterogeneous mixture of two gases because all gases mix uniformly with each other in all proportions. Gaseous solutions have the structure that is typical of all gases. Air, the gaseous solution with which we come in closest contact, is composed primarily of N2 (78 % by volume), O2 (21 %), and Ar (1 %), with smaller concentrations of CO2, H2O, Ne, He, and dozens of other substances at very low levels.

• Liquid solutions have the internal structure that is typical of pure liquids: closely spaced particles arranged with little order. Unlike a pure liquid, how ever, a liquid solution is composed of different particles. Much of this chapter is devoted to the properties of liquid solutions, and special emphasis is given to aqueous solutions, in which the major component is water.

• Two kinds of solid solutions are common. The first, the substitutional solid solution, exhibits a crystal lattice that has structural regularity but in which there is a random occupancy of the lattice points by different species.

Disperse systemsDisperse systems are called systems,

which consist of two phases, one of which is scattered or dispersed in other.

The disperse phase - phase which is scattered (dispersed) in medium.

The disperse medium - phase in which dispersion done.

Classification disperse systems

• By stat of dispersed phase and dispersed medium

By size of dispersed phase

• Colloidal solutions are disperse systems, which have dispersed phase particle, which size between 10-9 to 10-7m or 1 nm to 100 nm.

Concentration units of solution • Mass fraction (i) of solute in solution is the ratio of the

mass solute (mi) to the mass of solution mi +ms; ms- mass of a solvent:

• Percentage by weight (mass) or mass percent, is the quantity of one component of a so lution expressed as a percentage of the total mass:

• where m - percent by mass,• mA, mB, mC - mass of components in the solution.

• Mass concentration, titer (T) is number grams of solute (m) per one milliliter of solution (V). Or it is the ratio of the quantity grams of solute and volume solution:

T = m . V • Molarity (CM), or molar concentration, is the number of moles of solute dissolved

per liter of solution.

CM = γ = m . V MVwhere: CM - molarity (by mole of solute per liter of a solution);

γ - number mole solute;m - mass solute, grams;M - molar mass solute, in grams/mole;V - volume of the solution;• Molality is defined as the number of moles (γ) of solute dissolved per kilogram of

solvent. Thus, the molality of solute in a solution is

Cm = γ = msolute ; msolvent M solute msolvent

when Cm – molality (by mole of solute per kilogram of solvent);γ - number of moles of solute;m – mass of solvent.

• In measure analysis for the characteristic the composition of solution will use molar mass of an equivalent (equivalent mass)

• Molar mass of an equivalent of element is the mass of the element which combines with or displaces 1.008 parts by mass of hydrogen or 8 part by mass of oxygen or 35.5 parts by mass of chlorine: E = fequivalence · MB

• The factor of equivalence (fequiv) - number, which is demonstrated which part of matter (equivalent) can react with one atom of Hydrogen, or one electron in reduction reactions.

• Molar concentration of an equivalent (normal concentration), normality is quantity gram-equivalent of solute per one liter of solution (V):

• Ceq= γeq = m . V E Vwhere: CM - molarity (by mole of solute per liter of a solution);

γeq - number mole-equivalent of solute;m - mass solute, grams;E - molar mass of an equivalent solute (equivalent mass of solute);V - volume of the solution;

Henry's Law:Henry's Law:

The solubility of a gas dissolved in a liquid is proportional The solubility of a gas dissolved in a liquid is proportional to the partial pressure of the gas above the liquid.to the partial pressure of the gas above the liquid.

This is a statement of Henry's law, which can be written X = KPX is the equilibrium mole fraction of the gas in solution (its

solubility) P is its partial pressure in the gas phase K - constant of proportionality or Henry's-law constant.• The partial pressure is a part of common pressure,

which one is a share of each gas in gas mixture.

Properties of a solution which depend only on the concentration of the solute and not upon its identity are known as colligative properties.

• vapor-pressure lowering• boiling-point elevation• freezing-point depression• osmotic pressure.

The spontaneous mixing of the particles of the solute (present in the solution) and the solvent (present above the solution) to form а homogeneous mixture is called diffusion, just as the term is used for the spontaneous mixing of gases to form homogeneous mixtures.

A semi-permeable membrane - а membrane which allows the solvent molecules to pass through but not the solute particles.

The net spontaneous flow of the solvent molecules from the solvent to the solution or from a less concentrated solution to а more concentrated solution through а semi-permeable membrane is called osmosis (Greek: push).

• The osmotic pressure of а solution may thus be defined as the equivalent of excess pressure which must be applied, to the solution in order to prevent the passage of the solvent into it through а semi-permeable membrane separating the two, i.e. the solution and the pure solvent.

• Osmotic pressure may be defined as the equilibrium hydrostatic pressure of the column set up as а result of osmosis.

• Р С; Т; Р СТ or P=RCT • PV= nRT – van’t Hoff equation for dilute

solutions

Laws of osmotic pressure - These are the same as gas laws and apply to dilute solutions which occur in the living body

The effect of hypertonic and hypotonic solutions on animal cells.

(а) Hypertonic solutions cause cells to shrink (crenation);

(b) hypotonic solutions cause cell rupture;

(c) isotonic solutions cause no changes in cell volume.

The partial vapor pressure of a component in liquid solution is propor tional to the mole fraction of that component, the constant of proportionality being the vapor pressure of the pure component.

Raoult's law can be written as P1 = X1 P1

0

where P1 and P10 are the vapor pressure of the solution and that of the pure solvent,

respectively,X1 is the mole fraction of the solvent in the solution. P1 is the total vapor pressure of the solution. X2 = 1 - X2, P1 = (1- X2)P1

0

P10 - P1 is the vapor-pressure lowering

P10 - P1

---------- = X2 fractional vapor-pressure loweringP1

0 which can be seen to be equal to the mole fraction of the solute - X2.

The relationship between boiling-point elevation and solute concentration: it can be shown that in dilute solutions the boiling-point elevation is proportional to the molality of the solute particles.

if Tb, represents the boiling-point elevation: Tboiling =Tboiling (solution) - Tboiling (solvent), Tb = KbCm

Cm = molality, number of mole of solute per one kilogram of solvent

Where: Cm - molality of the solute in solution Kb- proportionality constant known as the molal

boiling-point elevation constant.

The relationship between freezing-point depression and molality in dilute solutions is a direct proportionality

Tf = Tfreezing(solvent) - Tfreezing(solution) - freezing-point depression

Tfreezing= KfCm

Where: Cm - molality of solute;

Kf - molal freezing-point depression constant

Thank you for attention