Experiment 4 Freezing Point Depression

Using the information content, H, to describe the structure at any temperature, it is possible to estimate the new temperature of water when a solute has been added. An increase in this temperature corresponds to the freezing point depression because the water must experience a greater decrease in temperature in order to arrive at the point of solidification. 

The freezing point depression constant for water is known from experiments and can be found in tables Tf = 1.858 ° C kg/mol. To calculate the freezing point, we must first determine the molality of the... 

Like freezing point depression and boiling point elevation, osmotic pressure is proportional to the concentration of solute molecules. Experiments show that osmotic pressure is proportional to both concentration (expressed as... 

Experiment 4 Determination of Molecular Mass by Freezing-Point Depression ... 

Most carbocations are too reactive to be directly observable in ordinary solvents, and until relatively recently evidence has been obtained indirectly, primarily through the study of reaction kinetics and trapping processes, experiments discussed in Sections 5.1, 5.2, and 5.4. Nevertheless, a few types of compounds have long been known to produce observable concentrations of positive ions relatively easily. The triarylmethyl derivatives were the first of this type to be investigated the halides ionize readily in non-nucleophilic solvents such as sulfur dioxide,70 and the alcohols yield solutions of the ions in concentrated sulfuric acid. Early observations by the freezing-point depression technique (see Section 3.2, p. 130) established that each mole of triphenyl carbinol yields 4 moles of ions in sulfuric acid, the reaction presumably being by way of Equation 5.14.71 Results in methane-sulfonic acid are similar.72... 

Ge and Wang also visualized the fuel cell cathode during cold start.6 Using a silver mesh as cathode GDL, they observed that when product water was less than 0.56 mg/cm2 water was not seen on the catalyst layer surface and that when it reached 1.12 mg/cm2 the liquid water emerged from the catalyst layer surface. This is consistent with the roughly estimated value of cathode catalyst layer water storage capacity of M).5 mg/cm2. They also estimated from their experiment that the freezing-point depression of water in the catalyst layer was at most 2°C. Then, they made the fuel cell optical... 

Using the average freezing point depression constant obtained for lauric acid in your experiment, calculate what would be the freezing point of a 10.0% w/w benzoic acid solution ... 

You used 0.5 M glucose and 3% NaCl aqueous solutions in your tonicity experiments. What would be the freezing points of each of these solutions, considering that the freezing point depression constant of water is 1.86°C/osmol ... 

Experiment 19 Colligative properties freezing point depression and osmotic pressure... 

In this experiment, the freezing-point depression of aqueous solutions is used to determine the degree of dissociation of a weak electrolyte and to study the deviation from ideal behavior that occurs with a strong electrolyte. 

For the determination of very high molar masses, freezing-point depressions, boiling-point elevations, and vapor-pressure lowerings are too small for accurate measurement. Osmotic pressures are of a convenient order of magnitude, but measurements are time-consuming. The technique to be used in this experiment depends on the determination of the intrinsic viscosity of the polymer. However, molar-mass determinations from osmotic pressures are valuable in calibrating the viscosity method. 

Judging from reports in the literature and the author s experience, one would think the preparation of the Schardinger dextrin acetates would be nearly fool-proof. Even so, widely varying optical rotations and other properties have been reported for these compounds. As has been seen, the variation in optical rotations, melting points, and freezing-point depression with different dextrin preparations has led to an abundance of confusion in this area. 

Boiling point elevation AT = mK[, (the constants have been tabulated) Freezing point depression AT = —mK (the constants have been tabulated) A solution in contact with its pure solvent across a semi-permeable membrane experiences an increase in pressure as pure solvent flows through the membrane into the solution. This osmotic pressure can be measured quite accurately, and through the equation ttV = nRT permits determination of the molecular weight of the solute. 

MNDO calculations, spectroscopic investigations, and X-ray analysis. It was also shown by freezing point depression experiments that the lithiated SAMP hydrazones exist in a monomeric form. Electrophilic attack by the electrophile on this system proceeds from the sterically more accessible face with high diastereoselectivity. 

A popular experiment uses freezing point depression to find the molar mass of an unknown solute. If a known mass of an unknown non-polar solute is placed into a known mass of a known non-polar solvent and the freezing point depression is measured, which of the following expressions will be equal to the molar mass of the unknown solute ... 

It would be impossible to determine the molar mass of this solute with a freezing-point depression experiment. (See Supplementary Problems 11 and 19.) ... 

Any of the colligative properties could be used to determine the activity coefficients of a dissolved substance whether it is an electrolyte or nonelectrolyte. The freezing-point depression is much used, because this experiment requires somewhat less elaborate equipment than any of the others. It has the disadvantage that the values of y can be... 

A common application of freezing-point depression and boiling-point elevation experiments is to provide a means to calculate the molar mass of a nonvolatile solute. What data are needed to calculate the molar mass of a nonvolatile solute Explain how you would manipulate these data to calculate the molar mass of the nonvolatile solute. 

PURPOSE OP EXPERIMENT Determine the molecular weight of an unknown solid by using the colligative property of freezing point depression. 

PURPOSE OP EXPERIMENT Prepare aspirin, determine its molecular weight by freezing point depression, and assay commercial aspirin by titration with NaOH. 

By referring to Experiment 20 (Freezing-Point Depression and Molecular Weight of an Unknown Solid), devise a reasonable method for determining the molecular weight of aspirin. Your instructor must approve an outline of your method and the quantities you plan to use before you begin work. Record all experimental data in TABLE 31.1C. 

For example, in an aqueous non-electrolyte solution with a mole fraction of Xb = 0.01, ATsi is about -1 K. An example from everyday life is shown in Experiment 12.10. A prime example of an application of freezing-point depression is, however, the melting effect of road salt. 

Activity coefficients of single ions cannot be measured directly. Instead, on the basis of experiments in which the free energy of an electrolyte is determined by various methods (such as by measuring freezing point depressions of solutions or by the measurement of the e.m.f. s of cells), a quantity called the mean ionic activity coefficient is obtained. For an electrolyte the mean ionic activity coefficient is defined as follows ... 

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