Soln Notes February 17, 2017

Transcription

1 Chapter 15 Solutions You are responsible for reading/notes on Section 15.4 Heterogeneous Mixtures p What is a SOLUTION? SOLUTE vs SOLVENT Characteristics of Solutions: Soluble/ Insoluble Solvation Immiscible/miscible Solubility Heat of Solution Endothermic- positive heat of solution; solute + solvent + heat à soln Exothermic - negative heat of solution; solute + solvent à soln + heat Factors that Affect Solubility Types of Solvent & Solutes Like Dissolves Like ; polar = water nonpolar = fats, oils, greases Chemistry Music Video 24: For Those About To Dissolve We Solute You Pressure Mainly for gases Gas solubilities in liquids increase with increasing pressure. Why??? Henry s Law - solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid (at constant temp) S1 = S2 P 1 P 2 Effervescence - Rapid escape of a gas from a liquid in which it is dissolved. Temperature As temp. increases, gas solubility decreases. Why? What happens with solids & liquids? Concentrations of Solutions Concentration: measurement of the amount of solute in a given amount of solvent or soln. Percent By Mass = number of grams of solute dissolved in g of solution EX: 3g sugar to 100g water What is the % by mass? Molarity, M = number of moles of solute in 1 L of soln (6M HCl means that there are 6 moles of HCl per every liter of soln) EX: 5 moles of NaOH in 1 L of soln Molality, m = Concentration of a soln expressed in moles of solute per kg of solvent. One molal soln EX: 0.3 moles of sugar in 500g of water. What is the "m"?

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3 What is the molarity of an aqueous solution containing 40.0 g of glucose (C ) 6 in 1.5 L of soln? H O 12 6

4 What is the molarity of a bleach soln containing 9.5 g of NaOCl per liter of bleach. Answer: 0.13 M Calculate the molarity of 1.60 L of a soln containing 1.55 g of dissolved KBr. Answer: M or 8.13 x 10-3 M How many grams of CaCl 2 would be dissolved in 1.0 L of 0.10 M soln of CaCl 2? 11 g

5 Electrolytes Nonelectrolytes produces ions (charge) does NOT produce ions Can Conduct Electricity Ionic Cpds & Some Polar Bonds Ex: NaCl No conduction Covalent Cpds (nonpolar) Ex: Sugar

6 Colligative Properties The presence of solutes cause solution to behave differently than their pure solvent. These new properties are called colligative properties. Colligative properties depend on the amount of particles dissolved, NOT the type of particles. 4 Types of Colligative Properties: Boiling Point Add more solute, BP goes UP!! Freezing Point Add more solute, FP goes Down!! Vapor Pressure Add Solute, VP goes down! Osmotic Pressure Osmosis is the process in which water moves across a semi-permeable membrane. It occurs because the water molecules are trying to reach equilibrium on either side of the membrane. Osmotic pressure is the amount of pressure required to prevent osmosis from occuring. Add solute, OP goes UP!

7 Colloids Solutions are homogeneous mixtures that do not separate. Homogeneous means that the particles are evenly distributed in the solution. A supsension contains larger particles that eventually settle out of the mixture (Ex. silt). A colloid is a heterogeneous mixture that contains small particles dispersed in a medium. (Ex: fog) Colloids can be solid, liquid, or gas. Foams, aerosols, and gels are common colloids.

8 Tyndall Effect Named for John Tyndall, the physicist who demonstrated that the particle in colloids were large enough to scatter light waves. A beam of light will pass through a solution without being seen. The same beam will be visible when it passes through a colloid because the particles are larger and disturb the light waves.

9 Colligative Properties Notes Colligative Properties The presence of solutes cause solution to behave differently than their pure solvent. These new properties are called colligative properties. Colligative properties depend on the amount of particles dissolved, NOT the type of particles. Vapor Pressure Depression The presence of a solute often causes the vapor pressure to drop. Thus is because the solute particles fill positions that are normally occupied by solvent molecules. Thus fewer solvent molecules escape the solution. Boiling Point Elevation The presence of solutes often raise the boiling point of the solutions. 1 mole of particles in 1 kg of water elevates the boiling point of water by degrees C. The more concentrated a solution is, the greater the boiling point elevation will be. Freezing Point Depression. Solutions freeze at lower temperatures than their pure solvents. A 1 molal solution of sugar in water freezes at deg. C. The more concentrated the solution, the more the freezing point will be lowered. Antifreeze Antifreeze affects both the boiling and freezing points of water. It prevents water in the radiator from freezing in the winter by lowering the freezing point and it prevents water from boiling in the summer because it also raises the boiling point of water. Osmotic Pressure Osmosis is the process in which water moves across a semi-permeable membrane. It occurs because the water molecules are trying to reach equilibrium on either side of the membrane. Osmotic pressure is the amount of pressure required to prevent osmosis from occuring. The more solute particle there are in a solution, the higher the osmotic pressure will be. Colloids Solutions are homogeneous mixtures that do not separate. Homogeneous means that the particles are evenly distributed in the solution. A supsension contains larger particles that eventually settle out of the mixture (Ex. silt). A colloid is a mixture that contains small particles dispersed in a medium. (Ex. fog) Colloids can be solid, liquid, or gas. Foams, aerosols, and gels are common colloids. Tyndall Effect Named for John Tyndall, the physicist who demonstrated that the particle in colloids were large enough to scatter light waves. A beam of light will pass through a solution without being seen. The same beam will be visible when it passes through a colloid because the particles are larger and disturb the light waves.