Freezing point depression constants

A = Kj- Cflj A 7b = Ki) Cflj We use molality in these equations because they describe temperature changes. The constant Zf is called the freezing point depression constant, and is called the boiling point elevation constant. These constants are different for different solvents but do not depend on the identity of the solutes. For water, Zf is 1.858 °C kg/mol and is 0.512 °C kg/mol. 

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... 

What is the freezing point depression constant of naphthalene ... 

The solution in question 3 freezes at -0.192°C. Because water normally freezes at 0°C, this means that the freezing point has decreased by 0.192°C. Thus, ATf = -0.192°C. What is the freezing point depression constant of water, Kfl... 

The depression of the freezing point of a solvent due to the presence of a dissolved solute is an example of a colligative property, that is, a property of a dilute solution that depends on the number of dissolved particles and not on the identity of the particles. Water has a freezing point depression constant, Kf, of 1.86 K kg mol-1. In other words, for every mole of nonvolatile solute dissolved in a kilogram of water, the freezing point of water is lowered by 1.86°C. The change in freezing point, A T, can be calculated from the equation... 

What was the molality of the naphthalene The freezing point depression constant for paradichlorobenzene is 7.1 °C ml. 

Impure substances have melting points that are very dependent upon the amount of impurity present. For a few substances this is quantified as the molal freezing point depression constant. The result is that melting points can be a very useful indicator of purification efforts. As long as each purification step in a process results in a higher melting point, the substance has been made more pure. This same concept allows the quality control chemist to have a very sensitive method for detecting impurities that is lower than anticipated. 

ATt is the number of degrees that the freezing point has been lowered (the difference in the freezing point of the pure solvent and the solution). Kt is the freezing-point depression constant (a constant of the individual solvent). The molality (m) is the molality of the solute, and i is the van t Hoff factor, which is the ratio of the number of moles of particles released into solution per mole of solute dissolved. For a nonelectrolyte such as sucrose, the van t Hoff factor would be 1. For an electrolyte such as sodium sulfate, you must take into consideration that if 1 mol of Na2S04 dissolves, 3 mol of particles would result (2 mol Na+, 1 mol SO) ). Therefore, the van t Hoff factor should be 3. However, because sometimes there is a pairing of ions in solution the observed van t Hoff factor is slightly less. The more dilute the solution, the closer the observed van t Hoff factor should be to the expected one. 

D—To calculate the molar mass, the mass of the solute and the moles of the solute are needed. The molality of the solution may be determined from the freezing-point depression, and the freezing-point depression constant (I and II). If the mass of the solvent is known, the moles of the solute may be calculated from the molality. These moles, along with the mass of the solute, can be used to determine the molar mass. 

Calculate the molality of the solution by dividing the change in temperature (AT) by the freezing-point depression constant (A)). 

IQ = molal freezing-point depression constant Kb = molal boiling-point elevation constant Kf for water = 1.86 K kg mol-1 for water = 0.512 K kg mol-1 AT = iKf x molality ATb = iKb x molality n = MRT... 

B) This problem can be solved using the factor-label method. The freezing point depression constant (kd for water is 1.86°C m ... 

Kf = molal freezing-point depression constant Kt,= molal boiling-point elevation constant A = absorbance a= molar absorptivity b = path length c= concentration Q = reaction quotient /= current (amperes) q= charge (coulombs) f= time (seconds)... 

A solution also exhibits a depression in its freezing point. The freezing point depression is the decrease in the temperature of the freezing point due to the addition of a solute. It is calculated using the equations ATj. = Kjm, where ATj. is the decrease in freezing point for the solution, Kj. is the molal freezing point depression constant, and m is the molality of the solution. Water s K. value is 1.86°C/m. 

For example, the observation that the freezing point of a 1 molal solution of acetone in sulfuric acid is depressed by twice the molal freezing-point depression constant of sulfuric acid is interpreted in terms of the reaction... 

A 0.01 molal solution of COH in H2S04 freezes at 10.09°C. The freezing point of pure H2S04 is 10.36°C, and the molal freezing-point depression constant is 6.81 °C. Explain. 

Molal Boiling-Point-Elevation Constants (Afb) and Molal Freezing-Point-Depression Constants (ACf) for Some Common Substances... 

PROBLEM 11.20 Assuming complete dissociation, what is the molality of an aqueous solution of KBr whose freezing point is —2.95°C The molal freezing-point-depression constant of water is given in Table 11.4. 

PROBLEM 11.25 A solution of 0.250 g of naphthalene (mothballs) in 35.00 g of camphor lowers the freezing point by 2.10°C. What is the molar mass of naphthalene The freezing-point-depression constant for camphor is 37.7 (°C kg)/mol. 

A solution prepared by dissolving 3.00 g of ascorbic acid (vitamin C, C HsOg) in 50.0 g of acetic acid has a freezing point that is depressed by AT = 1.33°C below that of pure acetic acid. What is the value of the molal freezing-point-depression constant for acetic acid ... 

Pure benzene freezes at 5.50°C and has a density of 0.876 g/mL. A solution of 1.7 g of nitrobenzene in 250 mL benzene freezes at 5.18°C. What is the molality-based freezing-point depression constant of benzene and at what temperature does a solution containing 3.2 g of bromobenzene in 250 mL of benzene freeze (You may make the ideally dilute approximation for both these solutions.)... 

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