Solutions CPS Chemistry

Definitions  Solutions A homogeneous mixture of two or more substances in a single phase  Soluble Capable of being dissolved

 Solvent Dissolving medium in a solution  What is doing the dissolving  Solute Substance dissolved in a solution  What is dissolved  Example Sugar in tea –  tea is solvent, sugar solute

Types of Solutions  May exist as gasses, liquids or solids  One component is designated as solvent and one as solute Chart on pg. 396

Phase  If there are two different types of substances it is a phase change Water + salt; water and gas  Same phase Water and apple juice  This is an aqueous solution  Means there is water involved Alcohol and liquid  Tincture solution  Means there is alcohol involved

Mixtures  2 or more substances when each retains its properties  Homogeneous Uniform distribution of particles nm size particles, can be atoms Can be physically separated Ex. Salt water, air Also called solution

 Heterogeneous Distribution of particles is not uniform Can be separated by physical means Particle size nm (nanometer)

Suspensions  When particles in a solvent are so large that they settle out unless stirred constantly  Gravity pulls particles to bottom of container

 Particles >1000nm in diameter, 1000 times as large as atoms  Ex. Italian salad dressing, muddy water  Can be separated by passing liquid through a filter

Colloids  Has particles that are intermediate in size and they remain dispersed in the solute  nm particle size  Emulsion or foam are specific types  Mayonnaise is an emulsion of egg and oil

The Tyndall effect  Is a sign that it may be a colloid  The particles are not large enough to be seen, but large enough to scatter light  Ex: headlights on a foggy night

Test tube Light Beam Test tube Light Beam Tyndall Effect, beam of light can be seen in suspensions and colloids No Tyndall Effect, beam of light cannot be seen in solutions

Electrolytes vs. Nonelectrolytes  Electrolyte A substance that dissolves in water to give a solution the ability to conduct electricity  Nonelectrolyte A substance that when dissolved in water to make a solution that does not conduct electricity

 When ionic compounds dissolve, the positive and negative ions separate from each other and are surrounded by water molecules  When the ions are free to move, electricity moves easily

How to Make Solutions  You need to know the: Solubility –the maximum amount solute can dissolve in a solvent Rate – how fast the solute dissolves

Factors that affect rate of dissolution  Surface area of the solute The larger the surface area, the more quickly it dissolves  Agitation of a solution When you stir or shake the solute particles are dispersed throughout the solvent, and it increase the rate of dissolution

Saturated Solutions  A solution that contains the maximum amount of dissolved solute is saturated  The factors that determine saturation are mass of solvent, mass of solute and the temperature  When a solution contains less than the maximum saturation it is considered unsaturated

Supersaturate  A solution that contains more dissolved solute than a saturated solution contains under the same conditions  But will form crystals when disturbed or cooled

Like dissolves like  The rule for predicting whether one substance will dissolve in another is related to the type of bonding, the polarity of a molecule and the intermolecular forces between the solute and solvent  Things need to be similar for them to dissolve

SolventSolute= Solution PolarPolar= yes Polarnon-polar= no NonpolarPolar= no Nonpolar Nonpolar= yes

Reminder molecule polarity

More Vocab.  Immiscible Liquid solutes and solvents that are not soluble in each other  Oil and water  Oil and salt  Miscible Liquids that dissolve freely in one another in any proportion  Water and food coloring

Back to Temperature- Solubility  Increase temp =increase KE= increase in solubility + increase in rate Higher temps dissolve faster( Liquids) BUT  Gasses act differently Increase temp = decrease solubility  Because gasses will leave solution at high temps

Pressure –solubility  There is no difference to solids or liquids, but with an increase in pressure it will increase the solubility of a gas For example CO 2 dissolved in a solution of sucrose and water (soda) will come out of solution when the pressure is decreased (opening the bottle, lets the soda bubble)

Size of the Particle – rate  Because the dissolution occurs only at the surface of the solute, when you crush a substance,  You get a larger surface, so you increase the rate at which it is dissolved

Stirring - rate  When you agitate the solvent, you increase the contact with the surface of the solute  You increase the rate

Amount of Solute -rate  As you increase the amount of solute you want to dissolve  You decrease the solubility and rate

Concentration  A measure of the amount of solute in a given amount of solvent or soulution  MATH IS INVOLVED

Molarity  The number of moles of solute in one liter of solution  Molar mass- as a reminder it is the mass listed on the PTE.. If it is for a compound, you simly add the masses of the atoms of the emperical formula  Ex. H 2 O H=1.00 O=15.99 total molar mass is =17.99g

Formula Amount of solute (mol) Molarity ( M) = ______________________ Volume of solution (L)

Practice  You have3.50 L of solution that contains 90.0 g of sodium chloride, NaCl. What is the molarity of that soulution?  Mass of solute 90.0  Solution volume = 3.50 L  Molar Mass if NaCl g/mol

Molality  Don’t confuse them…  The concentration of a solution expressed in moles of solute per kilogram of solvent  You measure the mass of the solvent…

Formula moles of solute (mol) Molality = ______________________ mass of solvent (Kg)

Practice  A solution was prepared by dissolving 17.1 g of sucrose C12H22O11 in 125g of water. Find the molal concentration  Given Solute mass = 17.1g sucrose  Solvent mass = 125 g H2O

Colligative Properties  Boiling- point elevation  Freezing-point depression  Vapor-pressure lowering  Osmotic pressure

 These change in relation to the total number of solute particles present  They are a constant that can be used to calculate the changes in solvents that contain nonvolatile solutes  Electrolytes have greater affects on colligative properties