Solutions Types of Mixtures, Rates of Solubility, and Molarity/Molality
Types of Solutions • Solutions • Soluble – capable of being dissolved • Solution – homogeneous mixture of two or more substances in a single phase • Components of Solutions • Solvent – dissolving medium in a solution • Solute – substance dissolved in a solution
Types of Mixtures • May exist in all states of matter (gas, liquid, solid) • Examples: • Oxygen and Nitrogen gas (gas/gas) • Carbon Dioxide in water (gas/liquid) • Water in air (Liquid/gas) • Alcohol in water (Liquid/Liquid) • Mercury in Silver (Liquid/Solid) • Sugar in water (solid/liquid) • Copper in Nickel (Solid/Solid)
Types of Solutions • Suspensions – particles in a solvent are so large that they settle out unless the mixture is constantly stirred or agitated • Colloids – particles that are intermediate in size between those in solutions and suspensions form mixtures known as colloidal dispersions • Tyndall Effect • Particles are sometimes large enough to scatter light. • Light is scattered by colloidal particles dispersed in a transparent medium • Gelatin in water = colloid • Sugar and water = true solution
Types of Solutions • Solutes: Electrolytes v. Nonelectrolytes • Electrolyte – substance that dissolves in water to give a solution that conducts electric current • Nonelectrolyte – substances that dissolves in water to give a solution that does not conducts electric current
The Solution Process • Factors Affect the Rate of Dissolution • Increasing the Surface Area of Solute • Agitating a Solution • Heating a Solvent
The Solution Process • Solubility • Solution equilibrium – the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates. • Saturated v Unsaturated • Saturated - solution that contains the maximum amount of a dissolved solute • Unsaturated – solution that contains less solute than a saturated solution under the existing conditions
The Solution Process • Supersaturated • A solution that contains more dissolved solute than a saturated solution contains under the same conditions • Solubility Values • The solubility of a substance is the amount of that substance required to form a saturated solution with specific amount of solvent at a specified temperature
The Solution Process • Solute – Solvent Interactions • Dissolving Ionic Compounds in Aqueous Solution • Hydration – solution process with water as the solvent is referred • When crystallized from aqueous solutions, some ionic substances form crystals that incorporate water molecules.
The Solution Process • Nonpolar Solvents • Ionic compounds are generally not soluble in nonpolar solvents such as carbon tetrachloride. • Non polar solvent molecules do not attract the ions of the crystal strongly enough to overcome the forces holding them together.
The Solution Process • Liquid Solutes and Solvents • Immiscible – liquid solutes and solvents that are not soluble in each other • Miscible – liquids that dissolve freely in one another in any proportion
The Solution Process • Effects of Pressure on Solubility • Increases in pressure increase gas solubilities in liquids • Henry’s Law – the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid. • There are no gas bubbles in an unopened bottle of soda because the pressure of CO2 applied during the bottling process keeps the carbon dioxide gas dissolved in the liquid. • Effervescence – rapid escape of a gas from a liquid in which it is dissolved
The Solution Process • Effects of Temperature on Solubility • Increasing the temperature usually decreases gas solubility • The effect of temperature on the solubility of solids in liquids is more difficult to predict. • Often increasing the temperature increases the solubility of solids • However, an equivalent temperature increase can result in a large increase in solubility in one case and only a slight increase in another.
The Solution Process • Heats of Solution • The net amount of heat energy absorbed or released when a specific amount of solute dissolves
Concentration of Solutions • Concentration – a measure of the amount of solute in a given amount of solvent or solution
Concentration of Solutions • Molarity • The number of moles of solute in one liter of solution • Molarity (M) = • Example: You have 3.50 L of solution that containes 90.0 g of sodium chloride. What is the molarity of that solution? • Given: solute mass = 90.0n g NaCl solution volume = 3.50 L • 90.0 g NaCl x = 1.54 mol NaCl • = 0.440 M NaCl
Concentration of Solutions • Now You Try • You have 0.8 L if 0.5 M HCl solution. How many moles of HCl does this solution contain? • To produce 40.0 g of silver chromate, you will need at least 23.4 g of potassium chromate in solution as a reactant. All you have on hand in the stock room is 5 L of a 6.0 M K2CrO4 solution. What volume of the solution is needed to give you the 23. 4 g K2CrO4 needed for the reaction?
Concentration of Solutions • What is the molarity of a solution composed of 5. 85 g of potassium iodide, KI, dissolved in enough water to make 0.125 L of solution? • How many moles of H2SO4 are present in 0.500 L ov a 0.150 M H2SO4 solution? • What volume of 3.00 M NaCl is needed for a reaction that requires 146.3 g of NaCl?
Concentration of Solutions • Molality • The concentration of a solution expressed in moles of solute per kilogram of solvent • Molality =
Concentration of Solutions • Example: A solution was prepared by dissolving 17.1 g of sucrose ( C12H22O11) in 125 g of water. Find the molal concentration of this solution. • Given: solute mass = 17.1 g sucrose • Solvent mass = 125 g water • 17.1 g C12H22O11 x = 0.0500 mol C12H22O11 • = 0.400 m C12H22O11
Concentration of Solutions • Now You Try! • A solution of iodine, I2, in carbon tetrachloride is used when iodine is needed for certain chemical tests. How much iodine must be added to prepare a 0.480 m solution of iodine in carbon tetrachloride if 100.0 g of CCl4 is used? • What is the molality of a solution composed of 255 g of acetone, (CH3)2CO, dissolved in 200 g of water? • What quantity in grams of methanol, CH3OH, is required to prepare a 0.244 m solution in 400 g of water?