Ch. 8 - Solutions How Solutions Form Solubility and Concentration

Definitions  Solution -  Solution - homogeneous mixture Solvent Solvent - present in greater amount Solute Solute - substance being dissolved

Definitions Solute Solute - KMnO 4 Solvent Solvent - H 2 O Solute: substance that is being dissolved Solvent: Substance doing the dissolving 99% of the time water is a solvent

Solutes can dissolve 3 Ways… Dissociation (Physical Change) Separating ionic compounds ( Ex. NaCl in water) The solvent and solute particles must attract one another in a dissociation. Example is NaCl (ionic compound) Water breaks up salt into its ions of Na and Cl.

Dispersion (Physical Change) Breaking down molecular or covalent compounds (Ex. Sugar in water) This involves breaking of a substance into small pieces that spread throughout the water. When enough water molecules surround sugar, its attraction is greater than the attraction holding the sugar together and it separates

Ionization (Chemical Change) Solute reacts with solvent to form new substances Ionization is a chemical change that involves a neutral atom gaining or losing electrons. An example is H 2 0 and HCl forming a hydronium ion and Cl -

Properties of Liquid Solutions Conductivity a.Solutes can change conductivity of a solution b.IONIC COMPOUNDS WILL CONDUCT ELECTRICITY Solid sodium chloride is a poor conductor of electricity. But when it is dissociated in water, the ions of sodium chloride can move freely allowing for current to flow.

Freezing/Boiling Point a.Increase or decrease based on amount of solute (salt lowers the freezing point of water – think sidewalks in winter) Solutions can increase or decrease the temperature for a phase change. MgCl 2 in salt spread on road during a snow storm lowers the freezing point of water. C 2 H 6 O 2 is a liquid used in antifreeze to increase the temp that water boils.

Heat of Solution During the formation of a solution energy is either released or absorbed. It can be described as we described chemical reactions – exothermic or endothermic Attractions among solute and solvent must be broken-this requires energy. Solutes dissolve and new attractions are formed releasing energy. The differences between energies is heat of solution.

Cold Packs Cold packs work by action of chemicals either releasing or absorbing heat when they dissolve in water. In cold packs water interacts with ammonium nitrate causing heat to be absorbed. Water dissolves ammonium nitrate causing temperature in the bag to drop cooling your injury.

Examples: Sodium hydroxide dissolves in water and becomes warmer Ammonium nitrate dissolves in water the solution becomes colder

Factors Affecting Rates of Dissolving 1.Surface Area 2.Stirring 3.Temperature

Warm Up  Explain what happens to the boiling point and freezing point of a solvent as the concentration of solute is increased in a solution.  Boiling point:  Freezing point:

Concentration Concentrated solution Concentrated solution –large amount of solute Dilute solution Dilute solution –small amount of solute Concentration = % of solute in a solution It Can be determined in mL or grams

Concentration Equations % by Volume: mL of solute/mL of solution X 100 usually liquid in liquid EX: 10% apple juice by volume = 10mL juice + 90mL water % By Mass: g of solute / mL of solution X 100 usually solid in liquid EX: 20% NaCl by mass = 20g NaCl + 80g water

Concentration Calculations mL of orange juice has 310 ml of pure orange concentrate in it. What is the concentration? 2. What is the concentration of 15 g of KoolAid in 85 mL of water? 3. A 600 mL solution contains 23% alcohol. What is the volume of the alcohol present?

Solubility Solubility = How readily a substance will dissolve or combine in another substance I.Saturated Solutions a.Contains as much solute as a solvents can hold b.Amount of Solute = Amount of Solvent II.Unsaturated Solutions a.Solution has less than the maximum amount of solute b.Amount of solute < Amount of solvent III.Supersaturated Solutions a.Contains more solute than the solvent can handle b.Amount of Solute > Amount of Solvent

SATURATED SOLUTION no more solute dissolves UNSATURATED SOLUTION more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration

Factors that Affect Solubility a.Polar vs Non-Polar b.Temperature c.Pressure

Solubility Solubility Curve Solubility Curve –shows the dependence of solubility on temperature

Solubility Solids are more soluble at... Solids are more soluble at... –high temperatures.  Gases are more soluble at... low temperatures. high pressures