CHE 132 Lecture Notes - Lecture 31: Freezing-Point Depression, Colligative Properties, Boiling-Point Elevation

DETERMINATION oF MOLAR EXPERIMENT 23 MASS FROM FREEZING POINT DEPRESSION EQUIPMENT AND CHEMICALS: Equipment 600 mL beaker Chemicals Cyclohexane (C Stir plate 100 ml. graduated cylinder Clamp Nonvolatile Unknowns Freezing point apparatus Spin vane 0.1 C Thermometer INTRODUCTION: When a solute is introduced into a pure solvent the newly formed solution will have certain physical properties that are from the solvent. As a of the presence of the the pressure of the solution will be lower than that of the pure solvent. As the vapor pressure is lowered there is a resulting increase in the amount of energy required to reach the boiling point of the solution. Conversely, the solution must cool to a lower temperature before a state change from liquid to solid occurs. These changes in physical properties vapor pressure lowering, boiling point elevation and freezing point depression are collectively referred to as colligative properties. These colligative properties, which also include osmotic pressure, do not depend on the nature of the nonvolatile solute in the solution but rather on the concentration of solute present. Because the properties are independent of the nature of the solute, they may be used to determine other properties of the solute such as molecular weight. The effect of a nonvolatile, nonelectrolyte solute on a pure solvent will be examined by finding the freezing point depression of a cyclohexane unknown so solution. The freezing point of a pure sample of cyclohexane will be determined. Introducing a nonelectrolyte solute should in solution formed to freeze at a lower temperature. This temperature will then be experimentally determined As stated the The molality of the solution dependent on the quantity of solute particles present in solution. (moles solute particles per kilogram of solvent) is directly proportional to the change in temperature between the freezing point of the pure solvent and that of the ATfss Kim The molal freezing point depression constant, K for cyclohexane is equal to 20.00 cfmolal By experimentally determining the freezing point depression of a ohexanel unknown solution, the molal concentration is easily calculated. In turn the molar mass of the unknown olute can be calculated as well Chemistry 132 EXPERIMENT23

QUESTION 8 1 points Save Answr What will the solution vapor pressure be for a solution of 9.13 mol of sucrose (C12H22011) dissolved in 1,000L of water at 20.0 °C? The vapor pressure of pure water at 20.0 "C is 17.5 torr QUESTION 9 1 points Save Answer Osmosis is the net motion of a solvent toward a region of lower solvent concentration from a region of higher solvent concentration. Or otherwise stated: the net movement of a solute from a region of higher solute concentration to a region of lower solute concentration. The important concept is that nature tries to disperse the solutes in a heterogeneous (liquid or gas phase) solution to produce homogeneous solution. This leads to a pressure that propels the components of the mixture. The equation used to describe this pressure is similar to the ideal gas law: TV InRT where n,R, T, and Vhave the same meanings as in the ideal gas law and IT is the osmotic pressure and i is the van't Hoff factor What is the osmotic pressure of 4.84 g of NaCl in 1.00 L of water at 20.0 "C QUESTION 10 1 points What are the units of osmotic pressure in the calculation above? psi atm kPa e All Answers Save and Subm Click Save and Submit to save and submit Click Save All Answers to sove all onswers