Unit 10: Properties of Solutions Tyna L. Meeks

Unit 6: Properties of Solutions Water is the only ordinary liquid found in our environment. Many substances dissolve readily in water, quite a few liquids are actually water solutions Many substances dissolve readily in water, quite a few liquids are actually water solutions Water based solutions are often called aqueous solutions, represented by an (aq) following chemical formula Water based solutions are often called aqueous solutions, represented by an (aq) following chemical formula

Unit 6: Properties of Solutions Even water that seems pure is never entirely so surface water contains dissolved minerals as well as other substances surface water contains dissolved minerals as well as other substances distilled water used in steam irons and car batteries contains dissolved gases from the atmosphere, as does rainwater distilled water used in steam irons and car batteries contains dissolved gases from the atmosphere, as does rainwater

Unit 6: Properties of Solutions Even water that seems pure is never entirely so Solutions - a unique homogeneous mixture Solutions - a unique homogeneous mixture when small amounts of salts are mixed with water, the salt may dissolve when small amounts of salts are mixed with water, the salt may dissolve – salt crystals separate into particles so small they can not be seen under any magnification – no Tyndall effect (light is not dispersed if a flashlight is shone through the solution)

Unit 6: Properties of Solutions Solutions always homogenous mixtures always homogenous mixtures – the salt that is dissolved is called the solute – the water, which does the dissolving, is called the solvent – dissolved salts will always give a positive result with a conductivity test. (The light bulb will illuminate, WHY?)

Unit 6: Properties of Solutions Solutions always homogenous mixtures always homogenous mixtures – the salt that is dissolved is called the solute – the water, which does the dissolving, is called the solvent – dissolved salts will always give a positive result with a conductivity test. (The light bulb will illuminate, WHY?) IONS

Unit 6: Properties of Solutions A solution can be any homogeneous mixture in the same physical state! - 2 solids: an alloy - 2 liquids: miscible - 2 gases: ALWAYS homogeneous Solutions do not disperse light, but they can be colored Solutions will never settle out a solid, they always pass through filters

Unit 6: Properties of Solutions Creation of a Solution: solid solute is added to water solid solute is added to water the solid crystals dissolve and disappear into the solvent the solid crystals dissolve and disappear into the solvent resulting solution is clear and colorless resulting solution is clear and colorless –What happens if a second, third, or even fourth scoop is added?

Unit 6: Properties of Solutions Dissolving process: So far, our discussion has been on the macroscopic level, but what is happening on the atomic and molecular level? Temperature, agitation and time all contribute to dissolving a material Temperature, agitation and time all contribute to dissolving a material How do the atoms and molecules interact to make this happen? How do the atoms and molecules interact to make this happen?

Unit 6: Properties of Solutions Dissolving process: Polar water molecules are attracted to other polar substances and to substances composed of electrically charged particles. These attractions make it possible for water to dissolve a great variety of substances. Dissolving a substance can be compared to a tug of war Dissolving a substance can be compared to a tug of war

Unit 6: Properties of Solutions in ionic crystals, positively charged cations are attracted to negatively charged anions, these attractive forces hold the crystal together in ionic crystals, positively charged cations are attracted to negatively charged anions, these attractive forces hold the crystal together substance will dissolve only if its ions are so strongly attracted to water molecules that the water tugs them out of the crystal substance will dissolve only if its ions are so strongly attracted to water molecules that the water tugs them out of the crystal

Unit 6: Properties of Solutions water’s positive end is attracted to the negative ion water’s positive end is attracted to the negative ion water’s negative end is attracted to the positive ion water’s negative end is attracted to the positive ion These intermolecular (between molecules) forces are called molecule- ion attractions These intermolecular (between molecules) forces are called molecule- ion attractions

Unit 6: Properties of Solutions

Dissolving includes competition among three types of attractions between solvent and solute particles between solvent particles themselves between particles within the solute crystals * Properties of both solute and solvent will affect whether two substances will form a solution

Unit 6: Properties of Solutions Dissolving also occurs following this simple guideline : “like dissolves like”

Unit 6: Properties of Solutions Colloids and Suspensions: Mixtures 2 types 2 types –heterogeneous: composition is not the same, or uniform, throughout a suspension is an example of these because the particles are large enough to settle out and can be separated by using a filter a suspension is an example of these because the particles are large enough to settle out and can be separated by using a filter

Unit 6: Properties of Solutions Colloids and Suspensions: Mixtures 2 types 2 types –heterogeneous: composition is not the same, or uniform, throughout a colloid is another example, the particles are not large enough to see without magnification, but they will scatter light (Tyndall effect) a colloid is another example, the particles are not large enough to see without magnification, but they will scatter light (Tyndall effect)

Unit 6: Properties of Solutions Colloids and Suspensions:

Unit 6: Properties of Solutions Solubility the ability of a solute to dissolve in a solvent the ability of a solute to dissolve in a solvent – soluble - can be dissolved – insoluble - cannot be dissolved the amount of solute able to dissolve in a given amount of solvent the amount of solute able to dissolve in a given amount of solvent – Table G

Unit 6: Properties of Solutions Be careful, the table lists the amounts able to dissolve in 100 g of water only. What about 200 g? 50 g? 50 g?

Unit 6: Properties of Solutions Each point on the slope of the line on graph represents an exact amount of solute that 100 g can possibly hold. SATURATED Below the line, more could be added UNSATURATED Above the line, extra amount of solute have been forced to go into solution SUPERSATURATED

Unit 6: Properties of Solutions Some salts are more temperature dependent than others - this can be observed by the slope of the line - the steeper the slope, the more dependent on temperature the salt is

Unit 6: Properties of Solutions Why do some of the slopes go downward?

Unit 6: Properties of Solutions Why do some of the slopes go downward? GASES Gases are inversely affected by temperature, the colder the temperature the more likely a gas is to dissolve!

Unit 6: Properties of Solutions Factors that affect Solubility size of the solute crystal? size of the solute crystal? vigor and duration of stirring? vigor and duration of stirring? The above factors can affect how fast a solute dissolves, but NOT how much. How much solute dissolves is a characteristic of the compound and cannot be changed

Unit 6: Properties of Solutions If a supersaturated solution is created, it is very unstable. Any excess motion or slight addition of more solute will cause the solution to begin to “snow” as excess solute falls out of solution as quickly as it can. - heat packs - rock candy

Unit 6: Properties of Solutions The general terms saturated and unsaturated are not always adequate for describing the properties of solutions that contain different amounts of solutes. A more precise description of the amount of solute in solution is needed - a quantitative measurement.

Unit 6: Properties of Solutions Solution concentration refers to the quantity of solute dissolved in a specific quantity of solvent or solution: solubility curves percents - part x 100% total total ppm - parts per million

Unit 6: Properties of Solutions Solution concentration refers to the quantity of solute dissolved in a specific quantity of solvent or solution: solubility curves Molarity = moles L

Unit 6: Properties of Solutions Dilutions: causing the concentration of a solution to change by adding more solvent M 1 V 1 = M 2 V 2

Unit 6: Properties of Solutions Kool-Aid Lab Calculate the molar mass of Kool-aid: Mass needed for a 0.1 M solution Mass needed for a 0.4 M solution Mass needed for a 0.7 M solution

Unit 6: Properties of Solutions Solubility Rules: Table F

Unit 6: Properties of Solutions Colligative Properties: a property of water that is altered by the addition of a compound to create a solution

Unit 6: Properties of Solutions Colligative Properties: a property of water that is altered by the addition of a compound to create a solution Boiling Point Elevation – adding a compound to water raises the boiling point of water 0.52 degrees for every particle added Particles are whole molecular compounds, or each ion present

Unit 6: Properties of Solutions Colligative Properties: a property of water that is altered by the addition of a compound to create a solution Freezing Point Depression – adding a compound to water lowers the freezing point of water 1.86 degrees for every particle added Particles are whole molecular compounds, or each ion present

Unit 6: Properties of Solutions Colligative Properties: a property of water that is altered by the addition of a compound to create a solution Vapor Pressure – can be altered if the substance added causes hydrogen bonds to be created – creating hydrogen bonds will lower the vapor pressure by creating stronger intermolecular forces of attraction