CHM120H5 Study Guide - Final Guide: Cyclohexene, Molality, Freezing-Point Depression

557 views13 pages

harlequinhound715

9 Feb 2016

School

Department

Course

Professor

For unlimited access to Study Guides, a Grade+ subscription is required.

Document Summary

Determination of a molar mass by freezing point. To determine the identification of an unknown compound chemists must first determine is molar mass1. The purpose of this experiment was to determine the molar mass of the unknown, non-volatile solute while analyzing the changes on the freezing point of a liquid solvent. In this work, the liquid is cooled to its freezing point while measuring for the time and temperature. With this, the moles of the solute can be calculated and this value is used to determine the molar mass of the unknown compound. The identification of the unknown compound"s molar mass was performed according to the procedure given in the lab manual (pages 42-45)1. The experiment was repeated 4 times, once with the pure solvent and three times with various concentrations of the unknown solute. The calculations were performed according to the same procedure1 and are presented in appendix i.

Related Questions

PARTS A,B,C ARE RIGHT. JUST NEED D, E, F

Another way that freezing point depression can be useful is toexperimentally determine the molar mass of an unknown solute in asolution. Use the data in the table to answer the questions belowand identify the unknown solute.

ExperimentalResults

Mass of solvent	10.234 g
Freezing point of pure solvent	24.0

magentadonkey275

Please help me solve for the molar mass of sample 1 and 2 and the molecular formula

Experiment 1084-03: Determination of M.M. by Freezing Point Depres sion Measure the freezing-point depressions solute whose empirical formula is known Pool the class hat occur with solutions containing mass of the solute and its Background Information However, as soon as the solution begins to freeze, Adding a solute to a pure, non-volatile lquid ature will remain constant untl all the (solvent) lowers the vapor pressure of the solvent raises its boiling point, and lowers (depresses) its freezing point. The extent to which these are aftected depends on the relative number of solute particlos in the solution. Properties of solutions that depend only on the number of solute molecules in a given quantity of solvent are called colligative properties. Such cyclohexane turns into solid. Once the substance again. The freezing point is the temperature where it stays constant, Le. the liquld phase and the sold phase of the cyclohexane coexists (Figure 3-1) boiling point elevation and osmotic pressure. They do NOT dopend on the nature of the solute, but DO depend on the nature of the solvent. As a consequence, colligative properties can be used to determine an unknown molar mass for a solute. In this experiment, we will be using cyclohexane (d " 0.779 gmL, K, . 20.5 oC/m) as the solvent to determine the molar mass of a white solid with an empirical formula of C,HC. The freezing point depression, Î7, is the difference between the freezing point of the pure solvent, TP, and the freezing point of the solution (solvent and solute). T As mentioned above, thits quantity is proportional only to the molal concentration of the solute, m Figure 3-1. Cooling Curves The proportionality constant, K, is called the freezing-point-depression constant. The K value of 20.5 C/m for Cyclohexane is one of the largest values one can find. Molal concentration is defined as the number of moles of substance in 1 kg of solvent. Now we can calculate the molar mass of a solute from ATã K,, the mass of the The freezing point of a solution in cyclohexane can be obtained in a similar way. Cooling results in an initial rapid decrease in the temperature until freezing begins as seen in the cooling curve of the pure solvent. However, the temperature of the solution does not remain constant while being frozen. As the cyclohexane in the solution treezes, cyclohexane is taken away from the solution and the concentration of the solute becomes higher In the liquid portion. Thus the molal concentration of the solute increases and the freezing point of the solute and the mass of the solvent. remaining liquid becomes lower. The result is a steadily decreasing freezing temperature until the solution is completely frozen. When all the solution In order to determine ATP, we will measure the freezing point of pure cyclohexane and the freezing point of a solution of the solute in is frozen, the temperature decreases more rapidly To evaluate the freezing point of pure cyclohexame, you will cool a sample of this substance, and measure the temperature as a The freezing point of the solution is the temperature at which the solution starts to freeze. portion represents the concentration of the starting function of time. As cooling begins, theOnly at this point, the concentration of the liquid temperature of the cyclohexane decreases rapidly.

CHM120H5 Study Guide - Final Guide: Cyclohexene, Molality, Freezing-Point Depression

Document Summary

Get access

Related Documents

CHM120H5 Lecture Notes - Lecture 1: Freezing-Point Depression, Vapor Pressure, Boiling-Point Elevation

CHM120H5 Lecture Notes - Lecture 3: Molality, 2Degrees, Supercooling

CHM120H5 Lecture Notes - Lecture 1: Freezing-Point Depression, Cyclohexane, Molar Mass

Related Questions