PLAN 1. The main concepts of solutions 2. Types of solutions 3. Heat effect of a dissolution 4. Methods for expressing the concentration of a solution 5. Vapour pressure and Raoult’s law 6. Collogative properties: 6.1 Relative lowering in vapour pressure 6.2 Elevation in boiling point 6.3 Depression in freezing point 6.4 Osmotic pressure 7 Van’t Hoff factor ‘i’ Colligative properties of nonelectrolyte’s solutions Assistant Kozachok S.S. prepared

A solution is a homogeneous mixture of two or more substances whose composition can be varied within certain limits

The substances making up the solutions are called components The components of a binary solution are solute and solvent. Solvent is a component which is present in excess, in other words a solvent is a substance in which dissolution takes place. Solvent doesn’t change its physical state during reaction of dissolution. Solute is a component which is present in lesser quantity. Or solute is a substance that dissolves

In a solution, the particles are of molecular size (about 1000 pm) and the different components cannot be separated by any of the physical methods such as filtration, setting,centrifugation, etc.) TYPES OF SOLUTION 1. Depending upon the total components present in the solution: a)Binary solution (two components) b) Ternary solution (three components) c)Quaternary solution (four components)…..etc. 2. Depending upon the ability of the dissolution some quantity of the solute in the solvent: a)Saturated solution b) Not saturated solution

3. Depending upon the physical states of the solute and solvent, the solution can be classified into the following nine type:

Out of the nine types of solutions, namely solid in liquid, liquid in liquid and gas in liquid are very common. In all these types of solutions, liquid acts as solvent. 4. According to the nature of solvent the solutions can be classified such as: a) aqueous solution – the solution in which water is a solvent; b) non- aqueous solution in which water is not the solvent (ether, benzene…) The basic rule for solubility is “like dissolves like” 5. Depending upon component’s solubility in liquid solutions (which are themselves liquids), these mixtures may be classified into the following three types: 1)The two components are completely miscible (ethyl alcohol in water) 2)The two components are almost immiscible (oil and water, benzene and water) 3)The two components are partially miscible (ether and water) 6. The binary solutions may be classified into two types: 1) Ideal solutions. Such solutions are formed by mixing the two components which are identical in molecular size, in structure and have almost identical intermolecular forces. In these solutions, the intermolecular interactions between the components (A-B) are of same magnitude as the intermolecular interactions in pure components ( A-A and B-B). Ideal solutions obeys Raoult’s law. 2) Non-ideal solutions

The mechanism of dissolving NaCl in the water Cl- Na +

Methods for expressing the concentration of a solution The concentration of a solution may be defined as the amount of solute present In the given quantity of the solution. 1.Mass percentage or volume percentage The mass percentage of a component in a given solution is the mass of the com ponent per 100 g of the solution.

2. Molarity It is the number of moles of the solute dissolved per litre of the solution. It’s represented as M or (М) = Moles of solute / Volume of solution in litres or (М) = Mass of component A/ Molar mass of A *Volume of solution in litres The unit of molarity is mol/L, 1L = 1000 ml 3. Molality It is the number of moles of the solute dissolved per 1000 g (or 1 kg) of the solvent. It’s denoted by m or (m) = Moles of solute/Weight of solvent in kg or (m) = Moles of solute * 1000/Weight of solvent in gram The unit of Molality is m or mol/kg

Molalty is considered better for expressing the concentration as compared to molarity because the molarity changes with temperature because of expansion of the liquid with the temperature 4. Normality It is the number of gram equivalents of the solute dissolved per litre of the solution. It’s denoted by N or (N) = Number of gram equivalents of solute/Volume of solution in litres or (N) = Number of gram equivalents of solute *1000/Volume of solution in ml Number of gram equivalents of solute = Mass of solute / Equivalent mass of solute

Methods f expression of solution’s composition Mass Mass particle ω, [%] Molar particle χ, [%] Molality С m, [mol/kilogram] Volume Molarity С м, [mol/L] Normality С N, [mol-equivalent./L] Titre Т, [g/ml]

Relationship between Normality and Molarity of Solutions Normality = Molarity * Molar mass/Equivalent mass 5. Mole fraction It is the ratio of number of moles of one component to the total number of moles (solute and solven) present in the solution. It’s denoted by X. Let suppose that solution contains moles of solute and moles of the solvent. Then

Vapour pressure and Raoult’s law vapour pressure The pressure exerted by the vapours above the liqud surface in equilibrium with the liquid at a given temperature is called vapour pressure The vapour pressure of a liquid depends upon 1.Nature of the liquid. The liquid, which have weaker intermolecular forces, tend to escape readily into vapour phase and therefore, have greater vapour pressure. 2.Temperature. The vapour pressure of a liquid increases with increase in temperature. This is due to the fact that with increase in temperature, more molecules will have large kinetic energies. Therefore, larger number of molecules will escape from the surface of the liquid to the vapour phase resulting higher vapour pressure.

The process of evaporation in a closed container will proceed until there are as many molecules returning to the liquid as there are escaping. At this point the vapor is said to be saturated, and the pressure of that vapor (usually expressed in mmHg) is called the saturated vapor pressure. Since the molecular kinetic energy is greater at higher temperature, more molecules can escape the surface and the saturated vapor pressure is correspondingly higher. If the liquid is open to the air, then the vapor pressure is seen as a partial pressure along with the other constituents of the air. The temperature at which the vapor pressure is equal to the atmospheric pressure is called the boiling point. evaporationtemperatureairatmospheric pressureboiling pointevaporationtemperatureairatmospheric pressureboiling point

Vapour pressure of solution Video

Vapour pressure of solution The vapour pressure of solution is found to be less than that of the pure solvent. Raoult’s law for Binary solutions of volatile liquids At a given temperature, for a solution of volatile liquids, the partial pressure of each component is equal to the product of the vapour pressure of the pure component and its mole fraction. Suppose a binary solution consists of two volatile liquids A and B. If and are the partial vapour pressure of the two lquids and a are their mole fractions in solution, then

Raoult’s law for solutions containing non-volatile solutes Vapour pressure of the solution=Vapour pressure of the solvent in the solution If is the vapour pressure of the solvent over a solution containing non-volatile solute and is its mole fraction then according to Raolt’s law, or At a given temperature, the vapour pressure of a solution containing non-volatile solute is directly proportional to the mole fraction of the solvent

Collogative properties The dilute solutions of non-volatile solutes exhibit certain characteristic properties which don’t depend upon the nature of the solute but depend only on the number of particles of the solute, on the molar concentration of the solute. These are called colligative properties. Thus 1.Relative lowering in vapour pressure 2.Elevation in boiling point 3. Depression in freezing point 4. Osmotic pressure This mean that if two solutions contain equal number of solute particles of A and B then the two solutions will have same colligative properties

Dependence general presser & partial pressure according to the concentration Concentration pressure

Diagram of the positive (А) & the negative (B) divergences from A Raoult’s law А Concentration А В В А

Dependence of the vapor pressure according to the nature of composition (for non ideal solutions) Vapour Liquid liquid + Vapour Concentration Curve of pair Curve of liquid

The curves of boiling (А) & freezing (B) for a pure water & solution (solvent) АБ Boiling of water tºtº Boiling of solution Time tºtº Freezing of water Freezing of solution time 0 100

The relative lowering in vapour pressure of an ideal solution containing the non-volatile solute is equal to the mole fraction of the solute at a given temperature. where A is a solvent, B is a solute

Elevation in boiling point The boiling point of a liquid is the temperature at which its vapour pressure becomes equal to the atmospheric pressure. The boiling point of the solution is always higher than that of the pure solvent. The different in the boiling points of the solution and pure solvent is called the elevation in boiling point It has been found out experimentally that the elevation in the boiling point of a solution is proportional to the molality concentration of the solution where is called molal elevation constant or ebullioscopicconstant

Depression in freezing point The freezing point is the temperature a which the solid and the liquid states of the substance have the same vapour pressure. The freezing point of the solution is always lower than that of the pure solvent. where is the molal depression constant or molal cryoscopic constant

Determination of Molar mass Conditions for getting accurate value of molar mass 1.The solute must be non-volatile. 2.The solution must be dilute, concentration of the solute in the solution should not be more than 5 % 3.The solute should not undergo either dissociation or association in the solution.

Osmotic pressure

OSMOSIS. It is the movement of water across a semi- permeable membrane from an area of high water potential (low solute concentration) to an area of low water potential (high solute concentration). It is a physical process in which a solvent moves, without input of energy, across a semi-permeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations water potentialsolutesolventwater potentialsolutesolventor Osmosis is the phenomenon of the flow of solvent through a semi-permeable membrane from pure solvent to the solution. Osmosis can also take place between the solutions of different concentrations. In such cases, the solvent molecules move from the solution of low solute concentration to that of higher solute concentration.

Difference between osmosis and diffusion

Osmotic pressure depends upon the molar concentration of solution Van’t Hoff observed that for dilute solutions, the osmotic pressure is given as:

Determination of Molar Mass from Osmotic Pressure

If two solutions have same osmotic pressure are called isotonic solutions or isoosmotic solutions If a solution has more osmotic pressure than some other solutrion, it is called hypertonic On the other hand, a solution having less osmosis pressure than the other solution is called hypotonic To note that a 0,9% solution of sodiun chloride (known as saline water) is isotonic with human blood corpuscles. In this solution, the corpuscles neither swell nor shrink. Therefore, the medicines are mixed with saline water before being injected into the veins. 5% NaCl solution is hypertonic solution and when red blood cells are placed in this solution, water comes out of the cells and they shrink On the other hand, when red blood cells are placed in distilled water (hypotonic solution), water flows into the cells and they swell or burst

7. Molecules of certain substances dissociate in a solvent to give two or more particles. For example: Consequently, the total number of particles increases in solution and, therefore, the colligative properties of such solutions will be large. Van’t Hoff factor ‘i’ to express the extent of association or dissociation of solutes in solution. It is the ratio of the normal and observed molar masses of the solute… In case of association, observed molar mass being more than the normal, the factor ‘i’ has a value less than 1. But in case of dissociation, the Van’t Hoff factor is more than 1 because the observed molar mass has a lesser value.

In case of solutes which do not undergo any association or dissociation in a solvent. Van’t Hoff factor ‘i’ will be equal to 1 because the observed and normal molar masses will be same. Since the molar mass are inversely proportional to the colligative property, Van’t Hoff factor may also be expressed as: i = Observed value of colligative property/Normal value of colligative propert Inclusion of Van’t Hoff (i) modifies the equation for colligative properties as follows: