Solutions

Characteristics of Solutions Forming Solutions Solubility

Forming Solutions Solution Aqueous solution Homogeneous solutions Uniformly mixed Solute + Solvent Solute: what is being dissolved Solvent: the substance that the solute is dissolved into Aqueous solution Solvent is water

Solubility “Like Dissolves Like” a given solvent can dissolve solutes that have similar polarities Polar dissolves in polar (So things like water dissolve get pulled apart) Non-polar dissolves in nonpolar (like oily organic stuff)

Different Solutes Ionic Substances Have a dipole Ions are attracted to the polar water molecules Can dissolve in water Polar substances Charged poles are attracted to the polar water molecules Nonpolar substances Do not have a dipole Cannot dissolve in water

Types of Solutions Solid Alloys Brass Liquid Sea water Gas Air

Solvation Process of solvent particles surrounding solute particles to create a solution The attraction between the solute and solvent overcome the attraction between the particles

Ionic vs. Covalent Substances connected by intermolecular forces Substances connected by electrostatic attractions Solvent break apart the crystalline solid form by the ions Breaks into individual ions Substances connected by intermolecular forces Hydrogen bonding Dipoles Solvent overcomes intermolecular forces to break apart the “clump” Breaks into molecules

Electrolytes vs. Non-Electrolytes Electrolytes: solutions that conduct an electric current Acids, bases, and salts dissolve in water to form conducting solutions Non-electrolytes→ solutions that do not conduct an electric current

Solution Composition Unsaturated Saturated Supersaturated More solute can be added to solvent at that temperature Saturated The maximum amount of solute is dissolved in the solvent at that temperature Supersaturated The amount of solute dissolved into the solvent is OVER the maximum amount at that temperature

Describing Solutions Dilute Small amount of solute is dissolved Concentrated Large amount of solute is dissolved Concentration [ ] shown sometimes as brackets A measure of the amount of solute in a given amount of volume

Factors Affecting Solubility Solubility: the ability to dissolve Surface area Stirring Temperature

Surface Area / Stirring Amount of area on the surface of a substance/object More surface area = faster rate More stirring = increase in rate Break away old particle exposing new one to repeat dissolving process

Average Kinetic Energy Temperature Average Kinetic Energy High temperature = Faster rate Causes solvent particles to move faster Most solids are more soluble at high temperatures Most gases are more soluble at low temperatures

Properties of Solutions Homogeneous Light goes through them Particles will NOT come out of solution They will go through fine filters

Calculations Parts Per Million or or Parts Per Billion or Mg of solute Cppm = L of solution Parts Per Billion or

Percentages Mass percent: Percents of the solution by mass Mass-volume percent: mass of solute in grams per 100mL of solvent Volume -volume percent: volume of solute in grams per 100mL of solvent Mass of solute (g) x 100 Mass of solution (g) Mass of solute (g) x 100 Volume of solution mL Volume of solute x 100 Volume of solution

Solubility Curves Curve that shows how many grams of solute can be dissolved into a given amount of solvent at different temperatures. How to Read a Solubility Curve Find the temperature on the (x-axis) Move up the substance line (curve) Slide over to the gram amount

Solubility Curves Continued If the amount is ABOVE the curve the solution is supersaturated If the amount is BELOW the curve the solution is unsaturated If the amount is RIGHT ON the curve the solution is saturated

Types of Soulubity Problems Am I saturated, unsaturated, or supersaturated ? How much more/less solute will be in solution if I raise/lower the temperature ? How much solute would saturate a solution of a DIFFERENT volume than the solubility curve ?

Solubility Problem of a different Volume Steps to solve Find saturation amount from the curve Make a table of values Setup a proportion using the information from the problem and curve Solve

Molarity The amount of mole per given volume of solutions Measurement of concentration Indicated by M Units are mol/L

Molarity by Dilution M1V1=M2V2 Dilute: to add more solvent without adding solute To determine the concentration of new solution M1V1=M2V2 M: Molarity defined as “moles per liter” V: Volume defined as “liters”

Colligative Properties physical properties of solutions that are affected by the number of solute particles but not the identity of dissolved solute particles Vapor Pressure Boiling Point elevation Freezing point depression

Vapor Pressure the pressure exerted in a closed container by liquids particles that have escaped the liquid’s surface & entered the gaseous state Lowers Vapor Pressure Adding a nonvolatile solute Less molecules of the solvent (water) are able to evaporate which lowers the VP

Boiling Point temperature at which the vapor pressure equals the atmospheric pressure in order for the solvent to escape the liquid state Boiling Point Elevation the temperature difference between a solution’s boiling point and a pure solvent’s boiling point Greater number of solute particles in solution the greater the boiling point is elevated Directly proportional relationship

Freezing Point The temperature when a solution goes from a liquid to a solid Particles become more organized Particle do not have enough KE to overcome their intermolecular forces Freezing Point Depression Difference in temperature between its freezing point and the freezing point of its pure solvent Particle interfere with the IMFs which lowers the FP The more particles of solute the lower the FP depresses

Molality Molality is used to calculate FP and BP problems Allows for other solvents to be used more easily

Colligative properties problems TB = (KB) (m) (i) TF = (KF) (m) (i) TB: Change in boiling point KB: Boiling point constant m: Molality i: number of particles (Van Hoff) TF: Change in freezing point KF: Freezing point constant i: number of particles (Van Hoff)

Steps to solve Calculate the molality Determine how many parts the solute breaks into Use the colligative properties equation Is it freezing ? Is it boiling? Solve for change in temperature add/subtract from original BP/FP BP adding FP subtraction

Solubility Review Not all compounds are soluble Completely soluble Slightly soluble insoluble Must check the solubility chart Solvent is water

Process to solve Write a balanced equation with phase indicators Balance for charge (subscripts) Balance for mass (coefficients) Determine if there is an insoluble product Separate all soluble compounds Do not separate insoluble compounds Cross out spectator ions Re-write the equations with ions/compound that contribute to the reactions 29

Sample Problem Ni 2+(aq) +2(OH 1-)(aq) → Ni(OH)2(s) 2 2 ____Ni(NO3)2 + ____NaOH → _____ Ni(OH)2 + _____ NaNO3 Ni 2+(aq) +2(NO3)1-(aq)+2Na1+(aq)+2(OH 1-)(aq) → Ni(OH)2 + 2Na1+(aq)+ 2(NO3)1-(aq) Ni 2+(aq) +2(OH 1-)(aq) → Ni(OH)2(s) (aq) (aq) (s) (aq) (s) (s) 30