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SOLUTIONS Mr. Kinton Honors Chemistry MIXTURES • Combination of 2 or more substances • Does not follow the law of definite proportions • Mixtures are either homogeneous or heterogeneous • Separated by physical means • Each of the substances in a mixture are called components HETEROGENEOUS MIXTURES • Do not have the same composition • Do not have do not have the same properties • Do not have a uniform appearance • Colloids and suspensions are specific types SUSPENSIONS • Heterogeneous mixture in which some particles settle • Able to settle due to their size and gravity acting on them • Typically will occur in a liquid medium COLLOIDS • Type of mixture where the particles dissolved are larger than normal but remain small enough to be suspended • Can occur as solids, liquids and gases • Tyndall Effect- the scattering of light by colloidal particles HOMOGENEOUS MIXTURES • Mixture that is uniform throughout • Can be in the solid, liquid or gaseous state • Also referred to as solutions • Forms when one substance disperses uniformly throughout another • With the exception of gaseous solutions, they all contain the condensed phase 7 TYPES OF SOLUTIONS TERMINOLOGY FOR SOLUTIONS • Solvent- the component of a mixture that is present in the greatest amount. • This component does the “dissolving” • Solute- the component of a mixture that is present in a smaller amount. • This component is being “dissolved” • Solubility- The amount of solute needed to form a saturated solution in a specific quantity of solvent • Solvation- occurs when the solvent completely surrounds the solute and breaks the intermolecular forces holding the solute together • Hydration- the process of solvation when water is the solvent THE SOLUTION PROCESS THE SOLUTION PROCESS • The solute and solvent must have similar attractive forces in order for a solution to form • When a solution is formed this is simply a physical change • When a solution energy is either absorbed or it is released • Endothermic- energy is absorbed, typically non-spontaneous (positive value) • Exothermic- energy is released, typically spontaneous (negative value) • ∆Hsoln = ∆H1 + ∆H2 + ∆H3 • • • • ∆H1 = Separation of solute molecules ∆H2 = Separation of solvent molecules ∆H3 = Formation of solute-solvent interactions ∆Hsoln = Enthalpy change of the solution or Heat of the solution ENTHALPY OF SOLUTION FORMATION ENTROPY • The amount of disorder present in a system • Processes that increase entropy tend to occur spontaneously • Solution formation is favored when entropy increases SOLUTIONS AND SOLUBILITY • Saturated solution- solution that is in equilibrium with the undissolved solute • Solute + Solvent Solution • Unsaturated solution- less solute is dissolved than possible for a given solvent • Supersaturated solution – solution that has been heated, additional solute has been added, and then the solution is cooled. • These solutions are extremely unstable SOLUBILITY CURVES • X-axis gives the temperature • Y-axis tells the amount of solvent being used • Allows us to know the saturation point of specific compounds • Be sure to look at the axes in order to properly answer questions! SOLUTE-SOLVENT INTERACTIONS • Increase when there are stronger attractions between solute and solvent • Hence “like dissolves like” • Miscible: liquids that mix in all proportions • Immiscible: liquids that do not dissolve each other PRESSURE • The amount of force applied on a given area of an object • Only impacts gases in solution • Increasing pressure causes an increase in gas concentration TEMPERATURE • Increase in temperature causes an increase in solid solubility • Increase in temperature causes a decrease in gas solubility TYPES OF SOLUTES Nonelectrolyte Weak Electrolyte Strong Electrolyte A Substance that does not form ions in solution Exist mostly as molecules with a small fraction of ions also Solutes that completely or nearly exist as ions Examples: Examples: Examples: Hydrocarbons Alcohols Other Molecules Weak Acids Weak Bases Strong Acids Strong Bases Salts- ionic compound formed by replacing the H+ of an acid CONCENTRATION • The amount of solute dissolved in a given quantity of solvent or solution • The more solute that is dissolved the more concentrated the solution will be • Concentration is not the same thing as the strength of the solution • What is the difference between concentration and strength? • We will often express concentration quantitatively rather than qualitatively CONCENTRATION Molarity Molality • M • m • Molarity equals moles of solute divided by volume of solution • Molality equals moles of solute divided by kilograms of solvent • Units are given as mol/L • Units are given as mol/kg • Electrolyte concentration can be expressed by the compound or the components • Electrolyte concentration can be expressed by the compound or the components EXAMPLE 1 • Calculate the molarity of a solution made by dissolving 23.4 grams of sodium sulfate in enough water to make 125 mL of solution. EXAMPLE 2 • What are the molar concentrations of each of the ions present in a .025 M aqueous solution of calcium nitrate? EXAMPLE 3 • A solution is made by dissolving 4.35 grams of glucose in 25.0 mL of water. Calculate the molality of glucose in the solution. DILUTION • Process in which a stock solution is made less concentrated by adding water • Moles solute before dilution = Moles of solute after dilution • M1V1=M2V2 • For diluting concentrated acids and bases add the acid or base to water EXAMPLE 1 • How many milliliters of 3.0M H2SO4 are needed to make 450 mL of .10M H2SO4?
