Introduction to Solutions and Osmotic Pressure PDF

BCM 221: INTRODUCTORY BIOCHEMISTRY STRUCTURE LECTURE 1 Introduction to Solutions and Osmotic pressure  Definitions Solution : solute plus solvent gives solution for which the properties is different from the reactants....

BCM 221: INTRODUCTORY BIOCHEMISTRY STRUCTURE LECTURE 1 Introduction to Solutions and Osmotic pressure  Definitions Solution : solute plus solvent gives solution for which the properties is different from the reactants. Solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance known as solvent. Solvent : the liquid in which a solute is dissolved to form a solution. Is the component of solution that is present in the greatest amount e.g water , ethanol, chloroform, acetone, n-hexane Solute : a substance that is dissolved in liquid. e.g sugar, salt , oxygen Osmolality is the osmotic pressure exerted by the number of moles per kg of solvent Osmolarity :the concentration of a solution expressed as the total number of solute particles per litre. Osmolarity means osmotic pressure exerted by the number of moles per liter of solution— Osmolarity, currently known as Osmotic concentration, is the measure of solute concentration expressed as molarity, The osmolarity of a solution is usually expressed as Osm/L  Definitions cont’d Molarity definition Molarity (M) is the amount of a substance in a certain volume of solution. Molarity is defined as the moles of a solute per liters of a solution. Molarity is also known as the molar concentration of a solution. Molarity formula and units The units of molarity are M or mol/L. A 1 M solution is said to be “one molar.” Molarity equation M = moles solute / liters solution Molality (m), or molal concentration, is the amount of a substance dissolved in a certain mass of solvent. It is defined as the moles of a solute per kilograms of a solvent Molality equation m = moles solute / kilograms solvent The unit of molality are m or mol/kg. The molality describes the moles of a solute in relation to the mass of a solvent, while the molarity is concerned with the moles of a solute in relation to the volume of a solution.  Definitions cont’d Molarity VS Molality  Definition cont’d Osmosis is the process by which solvent tends to move through a semipermeable membrane from a solution of lower concentration to a solution of higher concentration of solute to which membrane is relatively impermeable Osmosis is the spontaneous flow of solvent from a solution with a lower concentration of solutes to a more concentrated solution, with flow occurring across a semipermeable membrane. Osmotic pressure, the amount of force applied to a solution that prevents solvent from moving across a semipermeable membrane Total osmolality of the solution is the osmotic effect that would be exerted by the sum of all the dissolved molecules and ions across a membrane permeable only to water. Colloid is an aggregates of atoms or molecules in a finely divided state (submicroscopic), dispersed in a gaseous, liquid or solid medium and resisting sedimentation, diffusion and filtration. For example plasma albumin, blood, lipoprotein. Crystalloids, resembling a crystal in a body solution containing ions that can pass through a semipermeable membrane e.g Normal saline, Ringer’s lactate, Dextrose saline; as distinguished from a colloid which cannot do so. Crystalloids and water can easily diffuse across membranes, but an osmotic gradient is provided by the non-diffusible colloidal (protein and other higher MW) particles.  Definitions cont’d Tonicity, on the other hand, refers to the relative concentration of two solutions separated by a semipermeable membrane The difference between the osmosis and tonicity is based on what is considered for osmosis and tonicity. In case of osmosis, it is the water (or solvent) which moves across the membrane, while tonicity depends on the solutes which cannot move across the membrane Osmolarity takes into account the total concentration of penetrating solutes and non-penetrating solutes, whereas tonicity takes into account the total concentration of only non-penetrating solutes Filtration: filtration is the process by which fluid is forced through a membrane or other barrier because of a difference in pressure on the two sides Diffusion: is defined as the motion of a substance from a region of high concentration to one of low concentration  Pure?! Even though the water still looks ‘pure’, this term is wrong. Pure would mean there were only water particles, however we now have water particles + sugar particles! The sugar has not disappeared - instead it has dissolved in the water We would call the water + sugar a solution A solid dissolved in a liquid makes a solution In a solution the liquid is called the solvent, and the solid is called the solute Solute Solvent Solution Figure 1: Preparation of solution  They all sound the same! Solute Solvent Solution  These words need to be learned - however, be careful because they all sound pretty similar!  Solution - the mixture formed when a substance dissolves in it  Solute - the substance that dissolves  Solvent - the liquid in the solution  Dissolve - mixing of a substance in a liquid  Soluble - a substance which can dissolve (mix in a liquid)  Insoluble - a substance which cannot dissolve (mix in a liquid)  Solution Solution: a mixture of two or more substances that is identical throughout (homogeneous) can be physically separated Salt water is considered a composed of solutes and solventssolution. How can it be physically separated? the substance being dissolved the substance that dissolves the solute Iced Tea Mix Iced Tea Water (solute) (solution) (solvent)  Solution cont’d The solvent is the largest part of the solution and the solute is the smallest part of the solution S O L V E N T S O L U T E  Types of Solutions  On basis of solvent and solute, solution can be categorized into three as follows: 1. Gaseous solutions – air = Oxygen + Nitrogen 2. Liquid solutions – drinks = mix + water 3. Solid solutions – alloys = steel, brass, etc  On the basis of tonicity i. Isotonic solution ii. Hypotonic solution iii. Hypertonic solution  On the basis of Raoult’s Law, liquid-liquid solutions can be of two types. Ideal Solutions Non-ideal Solutions  Raoult’s law : Proposed by French chemist François-Marie Raoult in 1887, it states that the partial pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component (liquid or solid) multiplied by its mole fraction in the mixture Mole fraction –a fraction equal to the number of moles of a component, divided by the total number of moles in a solution Mole fraction = Xsolute=moles of solute/total moles of solution  Types of Solutions cont’d  Ideal solution: The solutions which obey Raoult’s Law at every range of concentration and at all temperatures are Ideal Solutions. We can obtain ideal solutions by mixing two ideal components that are, solute and a solvent having similar molecular size and structure. For Example, consider two liquids A and B, and mix them. The formed solution will experience several intermolecular forces of attractions inside it, which will be: A – A intermolecular forces of attraction B – B intermolecular forces of attraction A – B intermolecular forces of attraction The solution is said to be an ideal solution, only when the intermolecular forces of attraction between A – A, B – B and A – B are nearly equal  Types of solution cont’d Common examples of solutions are sugar in water and salt in water solutions, soda water, etc. In a solution, all the components appear as a single phase. Salt water is formed when salt (generally table salt) is mixed in water. Sugar water is formed by mixing sugar in water. Mouthwash consists of a number of chemicals dissolved in water. Tincture of iodine is obtained by dissolving crystals of iodine in alcohol.  What is a mixture? Mixture: a combination of two or more substances that do not combine chemically, but remain the same individual substances; can be separated by physical means. Two types: – Heterogeneous – Homogeneous  Homogeneous Mixture “Homo” means the same has the same uniform appearance and composition throughout; maintain one phase (solid, liquid, gas) Commonly referred to as solutions Example: Salt Water  Heterogeneous Mixture “Hetero” means “different” Consists of visibly different substances or phases (solid, liquid, gas) Can be separated by filtering Example:  Concentration the amount of solute dissolved in a solvent at a given temperature described as dilute if it has a low concentration of solute dissolved described as concentrated if it has a high concentration of solute dissolved  Concentration cont’d Unsaturated - has a less than the maximum concentration of solute dissolved Saturated - has the maximum concentration of solute dissolved (can see solid in bottom of solution) Supersaturated -contains more dissolved solute than normally possible (usually requires an increase in temperature followed by cooling)  Solubility the amount of solute that dissolves in a certain amount of a solvent at a given temperature and pressure to produce a saturated solution Factors affecting solubility of solids 1. Temperature 2. Shaking increased temperature causes solids to dissolve faster Shaking (agitation) causes solids to dissolve faster 3. Particle Size Smaller particles dissolve Faster because they have more surface area Note: Increasing the amount of solute DOES NOT increase the rate of dissolving  4. Polarity and Dissolving Chemists use the saying “like dissolves like”: Polar solutes tend to dissolve in polar solvents. Nonpolar solutes tend to dissolve in nonpolar solvents. Oil is nonpolar while water is polar. They are immiscible.  Miscible liquids can easily dissolve in one another. Immiscible liquids are not soluble in each other.  A point on the line is a saturated solution. Above the line is supersaturated. Below the line is unsaturated.  Assignments 1. What is solution? 2. Classify solutions with examples 3. Describe the factors that affect solubility 4. Write short note on the following: a. Concentration b. Mixture c. Osmolarity d. Diffusion e. Osmosis f. Properties of ideal solution THANK YOU!