LECTURE 1

1. LECTURE1 THEME: Coligative properties of biological liquids. Bases of titrimetric (volumetric) analysis. Complex compound in biological systems. ass. prof. Dmukhalska Ye.B. prepared

2. 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 7.

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

4. 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

5. 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: • Binary solution (two components) • Ternary solution (three components) • Quaternary solution (four components)…..etc. • 2. Depending upon the abilityof the dissolution some quantity of the solute in the solvent: • Saturated solution • Not saturated solution

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

7. 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: • The two components are completely miscible (ethyl alcohol in water) • The two components are almost immiscible (oil and water, benzene and water) • 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

8. 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. • Mass percentage or volume percentage • The mass percentage of a component in a given solution is the mass of the com ponentper 100 g of the solution.

9. 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

10. 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

11. 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

12. 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 • = Number of gram equivalents of solute/Volume of solution in litres • or • = 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

13. 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

14. Vapour pressure and Raoult’s law • The pressure exerted by the vapours above the liqud surface in equilibrium with the liquid at a given temperature is calledvapour pressure • The vapour pressure of a liquid depends upon • Nature of the liquid. The liquid, which have weaker intermolecular forces, tend to escape readily into vapour phase and therefore, have greater vapour pressure. • 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.

15. 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.

16. Vapour pressure of solution

17. 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

18. 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

19. 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 • Relative lowering in vapour pressure • 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

20. 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

21. 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

22. 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

23. Determination of Molar mass

24. Osmotic pressure

25. 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 or 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.

26. Difference between osmosis and diffusion

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

28. Determination of Molar Mass from Osmotic Pressure Conditions for getting accurate value of molar mass • The solute must be non-volatile. • The solution must be dilute, concentration of the solute in the solution should not be more than 5 % • The solute should not undergo either dissociation or association in the solution.

29. If two solutions have same osmotic pressure are called isotonic solutions or isoosmoticsolutions 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 sodium chlorine (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

30. The effect of hypertonic and hypotonic solutions on animal cells. • (а) Hypertonic solutions cause cells to shrink (crenation) - plasmolysis; • (b) hypotonic solutions cause cell rupture - hemolysis; • (c) isotonic solutions cause no changes in cell volume.

31. Titrimetry, in which we measure the volume of a reagent reacting stoichiometrically with the analyte, first appeared as an analytical method in the early eighteenth century.

32. Overview of Titrimetry: • Titrimetric methods are classified into four groups based on the type of reaction involved. • These groups are acid–base titrations, in which an acidic or basic titrantreacts with an analyte that is a base or an acid; complexometric titrations involving a metal–ligand complexation reaction; redox titrations, where the titrant is an oxidizing or reducing agent; and precipitation titrations, in which the analyte and titrant react to form a precipitate..

33. Typical instrumentation for performing anautomatic titration.

34. Equivalence Points and End Points • For a titration to be accurate we must add a stoichiometrically equivalent amount of titrant to a solution containing the analyte. We call this stoichiometric mixture the equivalence point. Unlike precipitation gravimetry, where the precipitant is added in excess, determining the exact volume of titrant needed to reach the equivalence point is essential. The product of the equivalence point volume, Veq, and the titrant’s concentration, CT, gives the moles of titrant reacting with the analyte. • Moles titrant = Veq. CT • Knowing the stoichiometry of the titration reaction, we can calculate the moles of analyte. Unfortunately, in most titrations we usually have no obvious indication that the equivalence point has been reached. Instead, we stop adding titrant when we reach an end point of our choosing. Often this end point is indicated by a change in the color of a substance added to the solution containing the analyte. Such substances are known as indicators.

37. Equipment for Measuring Volume • Analytical chemists use a variety of glassware to measure volume: beaker; graduated cylinder;volumetric flask; pipet;dropping pipet.

38. Beakers, dropping pipets, and graduated cylindersare used to measure volumes approximately, typically with errors of several percent. • Pipets and volumetric flasks provide a more accurate means for measuring volume. • Volumetricflask contains a solution, it is useful in preparing solutions with exact concentrations. The reagent is transferredto thevolumetric flask, and enough solvent isadded to dissolve the reagent. After the reagent is dissolved, additional solvent is added in several portions, mixing the solution after each addition. The final adjustment of volume to the flask’s calibration mark is madeusing a droppingpipet.

39. Pipets • A pipet is used to deliver a specified volume of solution. Several different • styles of pipets are available. Transfer pipets provide the most accurate • means for delivering a known volume of solution; their volume error is similar to • that from an equivalent volumetric flask

40. (a) (b) (c) (d) Common types of pipets and syringes: (a) transfer pipet; (b) measuring pipet;(c) digital pipet; (d) syringe.

41. Three important precautions are needed when working with pipets and volumetric flasks. First, the volume delivered by a pipet or contained by a volumetric flask assumes that the glassware is clean. Second, when filling a pipet or volumetric flask, set the liquid’s level exactly at the calibration mark. The liquid’s top surface is curved into a meniscus, the bottom of which should be exactly even with the glassware’s calibration mark. Before using a pipet or volumetric flask you should rinse it with several small portions of the solution whose volume is being measured.

42. Acid-base titrations • Based on acid-base reactions • The earliest acid–base titrations involved the determination of the acidity or alkalinity of solutions, and the purity of carbonates and alkaline earth oxides. Before 1800, acid–base titrations were conducted using H2SO4, HCl, and HNO3 as acidic titrants, and K2CO3 and Na2CO3 as basic titrants. End points were determined using visual indicators such as litmus, which is red in acidic solutions and blue in basic solutions, or by observing the cessation of CO2 effervescence when neutralizing CO32–. The accuracy of an acid-base titration was limited by the usefulness of the indicator and by the lack of a strong base titrant for the analysis of weak acids.

44. Titrations Based on Complexation Reactions • The earliest titrimetric applications involving metal-ligand complexation The use of a monodentate ligand, such as Cl– and CN–, however, limited the utility of complexation titrations to those metals that formed only a single stable complex. • The utility of complexation titrations improved following the introduction by Schwarzenbach, in 1945, of aminocarboxylic acids as multidentate ligands capable of forming stable 1:1 complexes with metal ions. The most widely used of these new ligands was ethylenediaminetetraacetic acid, EDTA, which forms strong 1:1 complexes with many metal ions. • Ethylenediaminetetraacetic acid, or EDTA, is an aminocarboxylic acid. EDTA, which is a Lewis acid, has six binding sites (the four carboxylate groups and the two amino groups), providing six pairs of electrons. The resulting metal–ligand complex, in which EDTA forms a cage-like structure around the metal ion, is very stable. The actual number of coordination sites depends on the size of the metal ion; however, all metal-EDTA complexes have a 1:1 stoichiometry.

46. Precipitation Titrations • A reaction in which the analyte and titrant form an insoluble precipitate also can form the basis for a titration. One of the earliest precipitation titrations, developed at the end of the eighteenth century, was for the analysis of K2CO3 and K2SO4 in potash. Calcium nitrate, Ca(NO3)2, was used as a titrant, forming a precipitate of CaCO3 and CaSO4. The end point was signaled by noting when the addition of titrant ceased to generate additional precipitate. The importance of precipitation titrimetry as an analytical method reached its zenith in the nineteenth century when several methods were developed for determining Ag+ and halide ions. • Pb2+(aq) + 2Cl–(aq) =PbCl2(s) • In the equilibrium treatment of precipitation, however, the reverse reaction describing the dissolution of the precipitate is more frequently encountered. • PbCl2(s) = Pb2+(aq) + 2Cl–(aq) • The equilibrium constant for this reaction is called the solubility product, Ksp, and is given as • Ksp = [Pb2+][Cl–]2 = 1.7.10–5

47. Titrations Based on Redox Reactions • Redox titrations were introduced shortly after the development of acid–base • titrimetry. • Since titrants in a reduced state are susceptible to air oxidation, most redox titrations are carried out using an oxidizing agent as the titrant. The choice of which of several common oxidizing titrants is best for a particular analysis depends on the ease with which the analyte can be oxidized. Analytes that are strong reducing agents can be successfully titrated with a relatively weak oxidizing titrant, whereas a strong oxidizing titrant is required for the analysis of analytes that are weak reducing agents.

49. Thank you for attention