Solutions and Solubilities All solutions have at least two parts: Solute: Solvent: Part of solution present in largest amount Substance that is dissolved, present in a smaller amount

What happens when you cool a solution or let it sit for a long time? Precipitates:A solid that comes back out of its solution due to a chemical reaction. Temp.

2 KI(aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2 KNO 3 (aq)

Why do solutes seem to disappear in a solvent? Whenever a solution forms, particles of the solute leave each other and become surrounded by particles of the solvent.

Why does the solute dissolve in a solvent? When a solute is dropped into a solvent, the solvent molecules “attack” the solute and pull it apart. Solvent- solvent interactions This happens only if the solvent-solute attraction is higher than the solvent-solvent interactions and solute-solute interactions.

Polarity of Water

Dilute: Concentrated: describes how much solute is present in a solution compared to the amount of the solvent These two terms are used when comparing the [ ] of two solutions with the same type of solute and solvent A mixture that has little solute dissolved in it A mixture that has a lot of solute dissolved in it Concentration

measurement that describes the limit of how much solute dissolves in a given amount (100 g) of solvent at a given temperature. Yet another CHARACTERISTIC PHYSICAL PROPERTY! - in other words, a measure of how well a solute dissolves in a solvent at a given temperature. Unsaturated solution: Saturated solution: A mixture in which more solute can dissolve A mixture that has the maximum amount of solute that can dissolve  HUH???  Solubility

Solubility in 100 g water at 0º C CompoundSolubility Salt (NaCl)35.7 Baking Soda (NaHCO 3 )6.9 Carbon Dioxide (CO 2 )0.348 Sugar (C 12 H 22 O 11 )180 Each compound listed in the table dissolves in water, but they have different solubilities. Which compound is the most soluble? Which compound is the least soluble?

Quiz 1.What two parts make up a solution? 2. If you are not part of the solution, you are part of the ___________________ 3.Two ways to describe the concentration of a solution are _______ and ___________________. 4.A ______________________ solution cannot hold any more solute at a given temperature. 5._____________ describes how well a solute dissolves in a solvent at a given temperature. 6.___________________describes how much solute is present in a solvent

Quiz-Answers 1.What two parts make up a solution? Solute and solvent 2. If you are not part of the solution, you are part of the ____precipitate____ 3.Two ways to describe the concentration of a solution are __dilute___ and ____concentrated________. 4.A _____saturated_______________ solution cannot hold any more solute at a given temperature. 5.__Solubility___________ describes how well a solute dissolves in a solvent at a given temperature. 6.Concentration_________describes how much solute is present in a solvent

Why doesn’t a solute added to a saturated solution dissolve?

Factors that Affect Solubility Temperature Nature of solute and solvent Pressure (gases only) (Not discussed here) In most cases, solubility increase with an increase in temperature (liquid-solid solutions). There are some exceptions to this. Gases are more soluble in colder solvents than in hotter solvents (liquid-gas solutions) Effect of temperature WHY? Entropy! Gases have highest entropy Liquids are in the middle. Solids have the lowest entropy

Factors that Affect Solubility Nature of the solute and solvent Size of molecule of the solute Attraction to solute/solvent particles

Factors that Affect Rate of Solution Rate of Solution: a measure of how fast a substance dissolves size of particles stirring amount of solute already dissolved temperature

Factors that Affect Rate of Solution Size of Particle Breaking up the solute into smaller pieces increases the surface area – area of contact between solute and solvent

Factors that Affect Rate of Solution Stirring Brings fresh portions of the solvent in contact with the solute, thereby increasing rate of dissolving

Amount of Solute Already Dissolved Factors that Affect Rate of Solution When there is little or no solute in solution, dissolving takes place relatively rapidly. As the solution approaches saturation, dissolving takes place more slowly.

Factors that Affect Rate of Solution For liquids and solid solutes, increasing the temperature not only increases the amount of solute that will dissolve but also increases the rate at which the solute will dissolve. For gases, the reverse is true. An increase in temperature decreases both solubility and rate of solution. Temperature

Solubility Curves - Used to determine the SOLUBILITY of a compound at a particular TEMPERATURE. - ON the curve indicates that the solution is SATURATED. -BELOW the curve indicates that the solution is UNSATURED. - ABOVE the curve indicates that the solution is SUPERSATURATED.

Solubility Questions What substance has a solubility of 90 g/100mL of water at a temperature of 25ºC ? At 45 degrees celcius, what is the solubility of sodium nitrate? At what temperature will sodium nitrate have a solubility of 95 g/100cm 3 What is the solubility of sodium chloride at 45 degrees celcius? What is the solubility of sodium chloride at 25ºC in 150 cm 3 of water ? 30 grams of potassium nitrate has been added to 100 mL of water at a temperature of 50ºC. How many additional grams of solute must be added in order to make it saturated?