module 4 colligative properties

• electrolyte: is a substance that forms ions when dissolved in water, which is then able to conduct a current (conductivity).
• When ionic compounds dissolve in water, the ions in the solid separate and disperse uniformly throughout the solution because water molecules surround and solvate the ions, reducing the strong electrostatic forces between them. This process represents a physical change known as dissociation.
• The pH scale, which measures acidity and alkalinity, was introduced by Søren Peder Lauritz Sørensen, a Danish chemist.
• Solutions


  Formed from the physical combination of different solutes and solvents
• Aqueous solution


  Water that contains one or more dissolved substances
• Electrolyte


  Substance that forms ions when dissolved in water and can conduct a current
• Dissociation of ions in water

  Ionic compounds dissolve in water, ions separate and disperse uniformly throughout the solution due to water molecules surrounding and solvating the ions
• Strong electrolyte


  • Completely ionized or dissociated in water, soluble, only ions are present
• Weak electrolyte


  • Not completely dissociated or ionized in water, reversible reaction with both ions and molecules present
• Nonelectrolyte


  Compound that does not ionize in solution and does not conduct electricity
• Glucose (sugar) or C6H12O6 is considered a nonelectrolyte as it does not dissociate into a solution
• Most soluble ionic compounds and few molecular compounds are strong electrolytes, while most molecular compounds are weak or nonelectrolytes
• Molality


  Number of moles of solute per kilogram of solvent, used when temperature is a concern as it is based on the mass of the solvent
• Molality is often used in comparing and determining colligative properties due to its accuracy in measuring solutes in solution when working with a range of temperatures or pressures
• Molality


  Based on the mass of the solvent used to create the solution because mass does not change as the temperature changes. It is a more accurate measure of solutes in solution when working with a range of temperatures (or pressure)
• Colligative properties


  • Physical properties of a solution that depend only on the number of solute particles present and not on the type of solute present. Include vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure
• Equilibrium vapor pressure


  The pressure of the vapor phase above the liquid when an equal amount of molecules are returning to the liquid state as they are escaping into the gas phase
• Vapor pressure lowering


  Determined by factors such as temperature, pressure, and intermolecular forces. Volatile liquids have high vapor pressure, while nonvolatile substances have low vapor pressure
• Addition of nonvolatile solute to solvent

  Limits the number of solvent molecules at the surface and increases solute-solvent interactions, making it difficult for solvent molecules to escape to the vapor phase
• Solute-solvent interactions


  Increases the difficulty for solvent molecules to escape to the vapor phase
• Vapor Pressure Lowering


  The presence of solute particles lowers the equilibrium vapor pressure of the solution compared to the pure solvent
• Greater concentration of solute in the solution

  Results in a greater reduction in vapor pressure
• The vapor pressure of an electrolyte solution will be lower than that of a weak electrolyte and a nonelectrolyte
• Difference between the vapor pressure of pure solvent (P0) and the vapor pressure of the solution (Ps)

  Termed as lowering in vapor pressure
• Relative lowering of vapor pressure

  Ratio (P0 – Ps)/P0
• Raoult’s Law


  Psolution = Xsolvent (Psolvent) where Psolution is the vapor pressure of the solution, Xsolvent is the mole fraction of solvent, and Psolvent is the vapor pressure of the solvent
• Boiling point is the temperature at which the vapor pressure of a liquid is equal to the atmospheric pressure
• Change in external pressure from 1 atm


  Results in a change in the boiling point
• A liquid with higher vapor pressure evaporates faster
• Addition of a nonvolatile liquid to a pure solvent

  Causes the vapor pressure of the solution to decrease
• A solution has lower vapor pressure than its pure solvent
• To make the vapor pressure of the solution equal to atmospheric pressure, the temperature of the solution needs to be increased
• It takes a higher temperature to attain the boiling point of a solution
• The vapor pressure of the solution decreases

  A solution has lower vapor pressure than its pure solvent
• To make the vapor pressure of the solution equal to atmospheric pressure

  We have to increase the temperature of the solution
• Boiling Point Elevation


  The difference in the boiling point of the solution and the boiling point of the pure solvent is termed as elevation in boiling point (∆Tb)
• Boiling Point Elevation


  The increase in boiling point (∆Tb) observed when a nonvolatile solute is dissolved in a solvent is directly proportional to the molal concentration of solute particles
• How to get the Van’t hoff factor

  1. NaCl → Na+ + Cl-

  2. Na has 1 ion (+1)

  3. Cl has 1 ion (-1)

  4. Thus, i = 2
• We add salt to boiling water when processing spaghetti in order to add flavor to the food
• The extent to which the vapor pressure of a solvent is lowered and the boiling point is elevated depends on the total number of solute particles present in a given amount of solvent, not on the mass or size or chemical identities of the particles