Starter S-161 Define Saturated solution Miscible Supersaturated solution

Chapter 16 Solutions

16.1 Properties of Solutions Chapter 16 16.1 Properties of Solutions

16.1 Solution Properties Solutions occur when a solute dissolves in a solvent Solutions are homogeneous mixtures Three factors determine how rapidly solutes dissolve Sink Hole Animation

16.1 Solution Properties Stirring – moves fresh solvent over the surface of the solute Temperature – particles move faster at higher temperatures, increase in frequency and force of collisions between solute and solvent Particle Size – smaller particles expose greater surface areas to the colliding solvent

16.1 Solution Properties Solubility – the amount of solute dissolved in a given amount of solvent Unsaturated – more solute can be dissolved at a specific temp Saturated – maximum solute that can be dissolved

16.1 Solution Properties Some liquids are infinitely soluble in each other. They are said to be miscible. Immiscible – liquids that are insoluble in each other Solubility is often given as grams of solute per 100g of solvent immiscible

16.1 Solution Properties A solubility curve gives the solubility (usually in grams solute per 100g solution) as it varies with temperature For most substances solubility increases with temperature Charts are for specific solvents You will need to read these charts for the test

16.1 Solution Properties Pressure has little effect on the solubility of liquids or solids Strong effect on the solubility of gases Henry’s Law – at a certain temperature, the solubility of a gas in a liquid is proportional to the pressure of the gas above the liquid

16.2 Concentrations of Solutions Chapter 16 16.2 Concentrations of Solutions

16.2 Concentrations of Solutions There are different ways to calculate how much solute is dissolved Concentration – the amount of solute dissolved in a solvent Dilute – small amount of solute Concentrated – large amount of solute

16.2 Concentrations of Solutions Molarity (M) – the number of moles of solute dissolved in one liter of solution Moles are calculated from the mass Volume must be in liters (convert from mL if necessary) Volume is the total final volume of the solution, not the volume of the solvent

16.2 Concentrations of Solutions Example: 0.90g NaCl is dissolved to make 100.0 mL of solution. What is the molarity of the soution?

16.2 Concentrations of Solutions Example: Household laundry bleach is a dilute aqueous solution of sodium hypochlorite. How many moles of solute are present in 1.5 L of 0.70M NaClO?

16.2 Concentrations of Solutions Often it is necessary to dilute a chemical. Make it’s molarity lower However, we can not reduce the number of moles in solution without a chemical reaction

16.2 Concentrations of Solutions Example: How many milliliters of aqueous 2.00M Magnesium Sulfate must be diluted with water to prepare 100.0 mL of 0.400 M Mangesium Sulfate? This means that 20.0 mL of the 2.00 M solution must be mixed with 80.0 mL of water (the solvent) to make the 0.400 M solution

16.2 Concentrations of Solutions Percent Solutions – can be expressed two ways Percent by mass

16.2 Concentrations of Solutions Example: How many grams of glucose is needed to make 2000.0g of a 2.8% by mass solution?

16.2 Concentrations of Solutions Percent Solutions – can be expressed two ways Percent by mass It helps often to remember that 1g of water equals 1 mL of water

16.2 Concentrations of Solutions Example: What is the percent volume of ethanol (C2H6O) in the final solution when 85 mL of ethanol is diluted by adding 165 mL of water?

16.3 Colligative Properties of Solutions Chapter 16 16.3 Colligative Properties of Solutions

16.2 Concentrations of Solutions Colligative Property – depends only on the number of solute particles, not their identity Vapor-Pressure Depression (lowering) Boiling-Point Elevation (increasing) Freezing-Point Depression

16.2 Concentrations of Solutions Vapor-Pressure Depression The surface of a liquid has particles that are constantly leaving the surface and some particles returning (equilibrium)

16.2 Concentrations of Solutions Vapor-Pressure Depression If a solute is dissolved in the solvent Not as many molecules can escape the surface

16.2 Concentrations of Solutions Vapor-Pressure Depression This reduces the amount of gas above the solution So the vapor pressure decreases

16.2 Concentrations of Solutions Vapor-Pressure Depression The decrease in a solution’s vapor pressure is proportional to the number of particles the solute makes in solution

16.2 Concentrations of Solutions Freezing-Point Depression When a substance freezes the particles take on an orderly pattern The addition of a solute disrupts this pattern More kinetic energy must be withdrawn form the solution to cause it to solidify

16.2 Concentrations of Solutions Freezing-Point Depression The difference in temperature between the normal freezing point of the solvent and the freezing point of the solution is called freezing-point depression

16.2 Concentrations of Solutions Freezing-Point Depression Salt is added to ice to lower the freezing point If enough salt it added, the freezing point is depressed and the ice turns to liquid

16.2 Concentrations of Solutions Boiling Point Elevation Boiling occurs when the vapor pressure of the liquid equals the atmospheric pressure Solutes decrease vapor pressure, so a solution must be at a higher temperature before it can boil

16.2 Concentrations of Solutions Boiling Point Elevation The difference between the normal boiling point of the solvent and the boiling point of the solution is called boiling point elevation

16.2 Concentrations of Solutions Remember that all colligative properties are proportional to the number of particles in solution The greatest effect would occur in a 50/50 solutions Antifreeze is mixed with water to increase the boiling point and to lower the freezing point