Solutions

Clear Targets

Mixture Basics  Homogenous – the different parts are unable to be seen  Heterogeneous – the different parts of a solution are able to be seen

Types of Mixtures  Solutions (homogenous) – a mixture that will remain mixed unless acted upon by an outside force (particle size is normally around 1 nm)  Suspension (Heterogeneous) - a mixture which contains large particles (normally over 1000 nm) of at least one of the ingredients. These large particles will settle out over time  Like clay in water  Colloid (Heterogeneous) – a mixture similar to a suspension in which the particles are a lot smaller (1 to 100 nm in size)

Colloids  Colloids are similar to both solutions and suspensions  They can be clear or seemingly one material like a solution, but they can be cloudy like a suspension when concentrated  Particles are in between the sized of solutions or suspensions.  The particles will not settle and cannot be filtered out like a suspension.

Colloids (properties)  Colloids have unique properties  Tyndall Effect  Browning Motion – when a colloid is looked under a microscope, it flashes light in a chaotic manner (called scintillations) because of its collisions between particles. These collisions keep the particles form settling.  Coagulation - colloidal particles tend to adsorb ions (almost always the same type of ions). The repulsive effect of these ions keep the colloidal particles from clumping together. Addition of another oppositely charged ion can cause them to coagulate (clump together and as the weight increases to settle out)

Emulsions  Emulsion – a colloid of a liquid in a liquid. Often the presence of an emulsifier (surfactant) is necessary. The surfactant is what keeps the colloidal particles from settling out.  emulsifier (surfactant) – a long molecule that is polar on one end and non polar on the other.

Review

Solubility (dissolving)  The solute and the solvent determine whether a substance will be dissolved.  Things like heat, agitation, and surface area determine how fast something dissolves.  This is because dissolution occurs on the surface of the solute. The more contact with the surface, the faster it will dissolve.  Agitation (stirring) causes more collisions between solute and solvent.  Heat- more kinetic motion between all particles  Surface area – the more surface are the more opportunity to dissolve (remember the mentos)

Solubility  When a substance is dissolved in a solution, there is a limit to how many particles can be dissolved.  What happens is when extra solute is added, it solvates (goes into solution by becoming ionized). At the same time, some of the ions join back together to become solid.  This happens at the same rate, so there is not net change in dissolved matter.

Solubility  A solution can only hold so much dissolved matter at a given temperature.  When a solution holds the maximum amount of matter possible, it is called a saturated solution. Otherwise it is called unsaturated.  Solubility is often expressed grams of solute per 100g of solvent

Miscible / Immiscible  Miscible – some liquids are infinitely dissolvable (the is no maximum amount of solute that will dissolve)  Water and ethanol  Immiscible – the exact opposite of miscible. These liquids never dissolve into each other  Oil and water, vinegar and oil

Factors of Solubitlity  Temperature – Temperature affects how much material a solution can hold.  If a solution of KNO 3 is saturated at 30  C and is allowed to cool 5 degrees, we would expect to see some solid Potassium Nitrate as it cools down. This is a result of a lower amount of solubility  Some solutions, like sodium acetate, can hold more material than expected in these situations. This is called a supersaturated solution.  It is in such a fragile condition that just one crystal of the sodium acetate will cause all of the material above that saturation point to crystallize.

Factors of Solubility

Colligative Properties  Colligative Properties – properties of a solution that have very little if nothing to do with the solute that is dissolved in it  Instead they depend upon the # of particles of the solute that are dissolved in it  There are 3 main properties that are colligative  Vapor pressure Lowering  Freezing point Depression  Boiling point Elevation

Vapor Pressure Lowering  Non volatile (not easily vaporized) solutions have a lower vapor pressure than pure solvent  The more free particles, the lower the vapor pressure will be.  The water surrounds the particles in a shell which is less able to break away to become a vapor.  Glucose – covalent 1 Particle (1x)  NaCl – ionic 2 particles (2x)  CaCl 2 – ionic 3 particles (3x)  (if these are at = molarities)

Freezing Point Depression  Again, the shells of solvation (shells of solvent around the particles) interfere with the freezing process (orderly arrangements of atoms)  The more particles – the more energy required to freeze it. The lower the freezing point  1 mol of a substance added to water drops the freezing point 1.86  C for every free particle  Glucose – 1 * 1.86  C  NaCl – 2 * 1.86  C  CaCl 2 – 3 * 1.86  C

Boiling Point Elevation  Boiling Point is the point where vapor pressure = atmospheric pressure  Since a solute lowers vapor pressure, it takes more energy to reach atmospheric pressure.  1 mol of a substance added to water raises the boiling point  C for every free particle  Glucose – 1 *  C  NaCl – 2 *  C  CaCl 2 – 3 *  C