1 / 15

Ch. 18 Solutions

Ch. 18 Solutions. Ch. 18.1 Properties of Solutions Ch. 18.2 Concentrations of Solutions Ch. 18.3 Colligative Properties of Solutions Ch. 18.4 Calculations Involving Colligative Properties. Ch. 18.1 Properties of Solutions. Solution formation

zofia
Download Presentation

Ch. 18 Solutions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ch. 18 Solutions • Ch. 18.1 Properties of Solutions • Ch. 18.2 Concentrations of Solutions • Ch. 18.3 Colligative Properties of Solutions • Ch. 18.4 Calculations Involving Colligative Properties

  2. Ch. 18.1 Properties of Solutions • Solution formation • Factors that affect whether or not a solution will form • Nature of the solute and the solvent • Factors that affect how fast a solute will dissolve • Stirring, temperature and surface area • Each factor involves the contact of the solute with the solvent

  3. Ch. 18.1 Properties of Solutions • Solubility • The solubility of a solution is the amount of solute that dissolves in a given amount of solvent at a given temperature to produce a saturated solution • In the formation of a solution, particles move back and forth between the solvated stage and the solid stage • There is no change in the overall system • A state of dynamic equilibrium exists between the solution and the undissolved solute (if T is constant)

  4. Ch. 18.1 Properties of Solutions • Solubility • Types of solutions • Saturated solution • Contains the maximum amount of solute for a given amount of solvent at a constant temperature • Unsaturated solutions • A solution that contains less solute than a saturated solution • Supersaturated solution • Contains more solute than should be theoretically possible at a given temperature (see pg. 506 – seed crystals) • Liquids can be miscible or immiscible • Miscible if they dissolve in each other • Immiscible if they do not dissolve in each other

  5. Ch. 18.1 Properties of Solutions • Factors affecting solubility • Temperature • The solubility of most solids increases as the temperature of the solvent increases • The solubility of gases decreases as the temperature of the solvent increases • Pressure • Gasses become more soluble as the partial pressure of the gas above the solution increases • Henry’s Law states that at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure of the gas above the liquid (see Sample Problem 18-1, pg. 507) • S1P2 = S2P1

  6. Ch. 18.2 Concentrations of Solutions • Molarity • The number of moles of solute dissolved per liter of solution (M) • Also known as molar concentration • Concentration is a measure of the amount of solute that is dissolved in a given quantity of solvent • A dilute solution is one that contains a low concentration of solute • A concentrated solution is one that contains a large amount of solute • Molarity is measured in moles of solute/liters of solution

  7. Ch. 18.2 Concentrations of Solutions • Making dilutions • Solutions can be made less concentrated by adding more solvent (diluting the solution) • Total number of dissolved moles does not change • Moles of solute before dilution = moles of solute after dilution (see Sample Problem 18-4, pg. 513) • M1V1 = M2V2 • There are several tools in the Chem Lab that can help with dilutions • Volumetric pipette • Volumetric flask

  8. Ch. 18.2 Concentrations of Solutions • Percent solutions • When using solutions in which both the solute and solvent are liquids, the concentration of the solute is expressed as a percent of the solution by volume • Expressed as volume/volume or v/v • Percent (mass/volume) is the number of grams of solute per 100ml of solution • The relationship among percent (mass/volume), solute mass, and solution volume is : • %m/v = mass of solute (g)/ solution volume (mL) x 100 • See Sample Problem 18-6, pg. 515)

  9. Ch. 18.3 Colligative Properties of Solutions • Colligative properties • Properties that depend only on the number of particles dissolved in a given mass of solvent • Vapor pressure reduction • Boiling point elevation • Freezing point depression

  10. Ch. 18.3 Colligative Properties of Solutions • Vapor pressure reduction • A solution that contains a non-volatile solute always has a lower vapor pressure than a pure solvent • Interferes with the intermolecular forces between the molecules in the solvent • The solution has a lower vapor pressure (p. 517) • The decrease in vapor pressure is proportional to the number of particles the solute makes in the solution • A solute that completely ionizes will have a greater effect on the vapor pressure than one that does not (pg. 518)

  11. Ch. 18.3 Colligative Properties of Solutions • Boiling point elevation • The difference in temperature between the boiling point of a solution and that of the pure solvent • Related to vapor pressure reduction • When the particle of solute interfere with the hydrogen bonding of water, vapor pressure is reduced • It takes much more kinetic energy to make the vapor pressure equal the atmospheric pressure (boiling) • It also takes more energy for the particles to escape the liquid • The boiling point increases with the addition of a non-volatile solute

  12. Ch. 18.3 Colligative Properties of Solutions • Freezing point depression • The difference in temperature between the freezing point of a solution and that of a pure solvent • The magnitude of the freezing point depression is proportional to the number of solute particles dissolved in the solvent • Does not depend on the identity of the solute • Addition of a solute interferes with the formation of crystals that form when a solution freezes • See example on pg. 519, middle of 3rd paragraph

  13. Ch. 18.4 Calculations Involving Colligative Properties • Molality and mole fraction • Colligative properties depend on solute concentrations • There are two ways to express the ratio of solute particles to solvent particles • Molality • Moles of solute/kg of solvent • Mole fraction • Ratio of the moles of solute in solution to the total moles of solution • X = molesA/ molesA + molesB

  14. Ch. 18.4 Calculations Involving Colligative Properties • Boiling point elevation and freezing point depression • Elevations and depressions are usually small • The magnitude of the boiling point elevation is directly proportional to the molal concentration, assuming the solute is molecular • The change in the boiling temperature is the elevation of the boiling point of the solvent rTb = Kb x m • Involves a molal boiling point constant (Kb) – the units are 0C/m • The boiling point elevation for an ionic solid depends on the number of ions produced by each formula unit

  15. Ch. 18.4 Calculations Involving Colligative Properties • Boiling point elevation and freezing point depression • The change in the freezing temperature represents the freezing point depression • Involves the molal freezing point depression constant (Kf) which is equal to the change in the freezing point for a I molal solution of a non-volatile molecular solute rTf = Kf x m • The units are 0C/m

More Related