Mr. Kinton Honors Chemistry 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 Strong Electrolyte Weak Electrolyte A Substance that does not form ions in solution Examples: Hydrocarbons Alcohols Other Molecules Exist mostly as molecules with a small fraction of ions also Examples: Weak Acids Weak Bases Solutes that completely or nearly exist as ions Examples: 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 Molarity equals moles of solute divided by volume of solution Units are given as mol/L Electrolyte concentration can be expressed by the compound or the components m Molality equals moles of solute divided by kilograms of solvent Units are given as mol/kg 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?