Essential Chemistry: Understanding Solutions & Definitions

Ch 1. SOLUTION Malvika Gaur Chemistry GRADE : xII Some Important Definitions 1. Mixture When two or more chemically non-reacting substances are mixed, they form mixture. 2. Heterogeneous Mixture It consists of distinct phases, and the observed properties are just the sum of the properties of individual phases. 3. Homogeneous Mixture It consists of a single phase which has properties that may differ from one of the individual components. 4. Solution The homogeneous mixture of two or more components such that at least one component is a liquid is called solution. 5. Solvent It is the constituent of solution which has same physical state as that of solution and generally present in greater amount than all the other components. 6. Solute The component of a solution other than solvent is called solute, may or may not have same physical state as that of solution. Generally it is in smaller amount. Ex- In a sugar syrup (liquid solution) containing 60% sugar (solid) and 40% water (liquinsend), water is termed as solvent, due to same physical state as that of solution. solutions Types of solutions ' Solid-liquid solution Most of the solids dissolve in one liquid or the other to form homogenous mixtures called solid-liquid solution When the amount of solute is much less as compared to the amountof solvent, the solution istermedas dilute solution In casethe amount of solute is relatively larger, the solution is known as concentrated solution. Liquid-liquid solution When two liquid are mixed together, the solution may be homogenous or not Depending upon the mutual miseitibility Completely miscible: When two liquid mixup together in all proportion to form homogenous mixtures they are said to-be completely miscible The mixing of two completely miscible liquids gives a true solution ~ Thecompletely missile liquids are of same nature i.e , they are either polar { alcohol and water } or non-polar { benzene and toluene} Partially miscible Some liquid fairs dissolve partially in each other to form twos distinct layer When mixed together. One layer consist of the solution of first component into the other while the second layer is the solution of second layer. Immisuble: When two liquids do not dissolve into each other and Form separate layer (each layer containing a pure component) they are saidto be immiscible or almost imeiscible solution Examples of such liquids are benzene-water carbon titrachloride- water etc two liquids are immiseible when one is polar and other one is non-polar In case of liquid-liquid system also, the chemically alike liquids dissolve in each other. Gas-liquid solution The solubility of the gas as in liquid defends upon several factors among these, the important ones are: a. Nature of gas b. Nature of liquid C.temperature d. Pressure Composition of solution The. Amout of solute dissolved in a particular amount of solvent is known as composition of solution or concentrationof solution Mass percentage (w/w) ' Mass percentage is defined asthe mass of solute in grams dissolved in per 100 gm of solution. Mass percent of solute: Mass of solute Mass of solute + mass of solvent * 100 i.e. Mass percent of solute Mass of solute Mass of solvent X 100 Molarity: The number of moles of solute dissolved per litres of the solution at a particular temperature is called molarity of the solution at that temperature It is denoted by M Molarity= Number of moles of the solute Volume of the solution in titres - Formality: The number of gram formula mass of an ionic solute dissolved per litre of solution particular temperature is called formality of the solution. Formality a solution =number of gram formula mass of solute Volume of solution in litres Molality Molality of a solution is defined as the number of moles ' of solute dissolved per 100gm of the solvent It is denoted by m Molality = number of moles of solute. Mass of solvent in kg Normality : The number of gram equivalent of the solute dissolved per litre of a solution at a particular temperature is called normality of the solution. Normality = Number of grams equivalent of solute Volume of solution in litres - Mole fraction : Mole fraction of particular component in a solution is the ratio of the number of moles of that component to the total number of moles of all the component present the solution. Mole fraction of a component = Number of moles of the given component total numbers of moles in the solution n - ·A - - HA ~At 4B HB = Nq+HB. Solubility Solubility of a substance is its maximum amount that can be dissolved in a specified amount of solvent at a specified temperature. It depends upon the nature of solute and solvent as well as temperature and pressure. Let us consider the effect of these factors in solution of a solid or a gas in a liquid. 1. Solubility of Solid in Liquid A solute dissolves in a solvent if the intermolecular interactions are similar in them, i.e., like dissolves like. Polar solute dissolves in polar solvent and non-polar solute in non-polar solvent. For e.g., sodium chloride and sugar dissolves readily in water and napthalene and anthracene dissolves readily in benzene. Solute + Solvent ⟶ Solution (i). Dissolution: When a solid solute is added to the solvent, some solute dissolves and its concentration increases in solution. This process is called dissolution. ii). Crystallization: Some solute particles collide with solute particles in solution and get separated out. This process is called crystallization. ( iii). Saturated solution: Such a solution in which no more solute can be dissolved at the same temperature and pressure is called a saturated solution . (iv). Unsaturated solution: An unsaturated solution is one in which more solute can be dissolved at the same temperature. (vi) Effect of temperature: In general, if in a nearly saturated solution, the dissolution process is endothermic, the solubility should increase with rise in temperature, if it is exothermic, the solubility should decrease with rise in temperature. (vii) Effect of pressure: Solids and liquids are highly incompressible, so pressure does not have any significant effect on solubility of solids and liquids. (vii) Supersaturated solution: When more solute can be dissolved at higher temperature in a saturated solution, then the solution becomes supersaturated. , 2. Solubility of ' Gas in Liquid ' All gases are soluble in water as well as in other liquids to a greater or lesser extent. The solubility of a gas in liquid depends upon the following factors Nature of the gas, Nature of solvent, Temperature and Pressure. Generally, the gases which can be easily liquified are more soluble in common solvents. For e.g., CO2 is more soluble than hydrogen or oxygen in water. The gases which are capable of forming ions in aqueous solutions are much more soluble in water than other solvents. For e.g., HCl and NH3 are highly soluble in water but not in organic solvents (like benzene) in which they do not ionize. i) Effect of temperature: Solubility of most of the gases in liquids decreases with rise in temperature. In dissolution of a gas in liquid, heat is evolved and thus this is an exothermic process. The dissolution process involves dynamic equilibrium and thus follows Le Chatelier’s principle. As dissolution is exothermic the solubility of gas should decrease with rise in temperature. (ii) Effect of pressure: Henry’s law - At constant temperature, the solubility of a gas in a liquid is directly proportional to the pressure of the gas. p = KH x, KH = Henry’s law constant. Applications of Henry’s law 1. In manufacture of soft drinks and soda water, CO2 is passed at high pressure to increase its solubility 2. To minimise the painful effects accompanying the decompression of deep sea divers. O2 diluted with less soluble. He gas is used as breathing gas. 3. At high altitudes, the partial pressure of O2 is less then that at the ground level. This leads to low concentrations of O2 in the blood of climbers which causes ‘anoxia’. i). Nature of liquid : Liquid with higher intermolecular attraction forces form less amount of vapour and hence lower vapour pressure and vice-versa. ii). Temperature : Vapour pressure increases with temperature of liquid. This is because, as temperature increases, kinetic energy of the molecules increases, hence, more molecules leave the surface of the liquid and come into vapour phase. Intensive, extensive and colligative properties intensive properties The properties which do not depend-upon the quantityof matter present in the system are called intensive properties For example: temperature, density, concentration, specific heat, viscosity, surface tension,etc. Extensive properties: The properties which depend upon the quantity of matter present in the system is called extensive properties For example: Number of moles, mass, volume, enthalpy, entropy free energy Colligative properties: Solution exhibit certain very important and interesting properties These properties are related to the number of solute and solvent particles present in the solution and do not depend upon the nature of solute The properties of solution which depend upon the numberof solute particular present in a definite amount of solvent but not the chemical nature of solute are called colligative properties. The important colligative properties of solution are as follows: Relative lowering of vapour pressure The elevation of boiling point The depression of freezing point Osmotic pressure. Non-volatile, non-electrolytic solute, electrolytic solute,dissociation and association. Non -volatile substance which dissolve in water to form solution can broadly be classified into following. a. non-electrolytic solute : Th'e solute which do not ionise in solution . # due to absence of ions, their solution do not conduct electric current. e.g.→ sugar,urea, glucose, etc. b.electrolytic solutes : The solute which dissociate into ions in aqueous solution. # these are mostly ionic compound and possess oppositely charged ions held together by electrostatic forces of attraction. # polar covalent compound may also act as electrolytic solutes ' due to presence of oppositely charged ions, the solution of an electrolytic solute conducts electric current. Strong electroytes. NaCl KCl KBr NH4Cl K2SO4 Weak electrolytes CH3COOH Na4OH HCN