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Solutions Ch 15 & 16. What is a solution?  A solution is uniform mixture that may contain solids, liquids, or gases.  Known as a homogenous mixture.

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Presentation on theme: "Solutions Ch 15 & 16. What is a solution?  A solution is uniform mixture that may contain solids, liquids, or gases.  Known as a homogenous mixture."— Presentation transcript:

1 Solutions Ch 15 & 16

2 What is a solution?  A solution is uniform mixture that may contain solids, liquids, or gases.  Known as a homogenous mixture  Solution = solute + solvent  Solvent – The substance in greater abundance in the solution  A solvent dissolves the solute. (dissolving medium)  Solute – The substance dissolved in the solvent

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5 Characteristics of Solutions  Soluble – The solute’s ability to dissolve in a solvent  Insoluble – The solute is not able to dissolve in a solvent  Immiscible – Two liquids that can be mixed together, but separate shortly after you stop mixing them  Miscible – Two liquids that are soluble in each other

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7 Solvation in Aqueous Solutions  Solvation – The process of surrounding solute particles with solvent particles to form a solution  Aqueous solution – A solute dissolved in water  Caused by constant, random molecular motion of solute and solvent particles. (Remember KMT)  In an aqueous solution each ion is surrounded by water molecules  Individual solute ions break away from the crystal and the charged ions become surrounded by solvent molecules (H 2 O) and the ionic crystal dissolves

8 Solvation Process

9 Rules for Solvation  Like dissolves like  Polar molecules dissolve polar molecules  Non-polar molecules dissolve non-polar molecules Polar MoleculeNon-polar Molecule Equal distribution of electrons CO O O HH H2OH2O CO 2

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11 Factors that Affect Rate of Solvation (How fast something dissolves)  Need to increase collisions between solute and solvent molecules 1. Agitating the mixture (Stirring)  New collisions between solute and solvent will occur 2. Increasing the surface area of the solute (Crushing the solute)  Greater surface area allows more collisions to occur 3. Increasing the temperature of the solvent  Increases kinetic energy of molecules and more frequent collisions occur 4. Increasing the pressure (For gases)  Increases the rate of collision between particles.

12 Solubility (How much is dissolved)  Solubility – The maximum amount of solute that will dissolve in a given amount of solvent at a specified temperature and pressure.  Solubility is usually expressed in grams of solute per 100 g of solvent or in grams/liter.

13 Solubility cont...  Saturated solution contains the maximum amount of dissolved solute for a given amount of solvent at a specific pressure and temperature.  In a saturated solution, solvation and crystallization are in equilibrium (They are happening at equal rates at the same time.)  Unsaturated solution contains less dissolved solute for a given temperature and pressure than a saturated solution  Supersaturated solution contains more dissolved solute than a saturated solution at the same temperature  A supersaturated solution is made at high temperatures, cooled slowly, and is unstable

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15 Factors That Affect Solubility (How much is dissolved) 1. Temperature  Most substances as temperature increases solubility increases  Gases are the exception and solubility tends to decrease as temperature increases, because they are moving quickly escaping the solvent 2. Pressure (For Gases Only)  The solubility of a gas in any solvent increases as the pressure above the solution increases, keeping the gas from escaping in the solvent

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19 Henry’s Law (Pressure and Solubility of a Gas)  Henry’s Law states that at a given temperature the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) 

20 Describing Solutions - Electrolytes  Electrolytes are compounds that dissociate or ionize in water to form a solution that conducts an electric current  To dissociate or ionize means to break apart into individual ions  Ionic compounds are electrolytes because they dissociate into ions  When NaCl is dissolved in water it breaks up into Na+ and Cl- ions.

21 Electrolytes dissociate into individual ions and conduct an electric current

22 Strong ElectrolyteWeak ElectrolyteNonelectrolyte Conducts a strong current. NaCl Conducts a weak current. HgCl 2 Does not conduct a current. Sugar water

23 Strong and Weak Electrolytes  A strong electrolyte conducts a strong current and the compound has completely dissociated into ions  NaCl  A weak electrolyte conducts a poor current because only part of the solute exists as ions.  NH 3 (Ammonia)  A nonelectrolyte does not dissociate or form ions, thus does not conduct a current.  Most molecular compounds are nonelectrolytes  Sucrose (sugar)

24 Solubility Example 1 If the solubility of NaCl at 25˚C is 36.2 g/100 g H2O, what is the maximum mass of NaCl that can be dissolved in 200.0 g of H 2 O at the same temperature?

25 Solubility Example 2 If the solubility of KNO 3 at 20 ˚ C is 79 grams in 250 grams of water, what is the solubility in grams per liter?

26 Henry’s Law Example The solubility of a gas is 0.35 g/L at 25.0 kPa of pressure. What is the solubility when the pressure is increased to 115 kPa?


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