Calculations boiling-point elevation

When the concentration of sugar reaches 66%, you are at the maple syrup stage. The calculated boiling point elevation (660 g of sugar, 340 g of water)... 

Table XXVII.—Comparison of Calculated Boiling Point Elevation, Freezing Point Depression, and Osmotic Pressure...

Since pure water freezes at 0°C, the solution will freeze at -7.79°C. We can calculate boiling-point elevation in the same way as follows ... 

Remember to use molality (m) and not molarity (M) when calculating boiling point elevation or freezing point depression. 

Calculating Boiling-Point Elevation and Freezing-Point Depression... 

Calculating boiling-point elevation and freezing-point depression Given the molality of a solution of nonvolatile, undissociated solute, calculate the boiling-point elevation and heezing-point depression. (EXAMPLE 12.10)... 

The molal boiling-point and freezing-point constants are used to calculate boiling-point elevations and freezing-point depressions of solvents containing nonvolatile solutes. 

The freezing point depression and boiling point elevation techniques are useful in calculating the molar mass of a solute or its van t Hoff factor. In these cases, you will begin with the answer (the freezing point depression or the boiling point elevation), and follow the same steps as above in reverse order. 

In freezing-point depression and boiling-point elevation problems, to find the actual freezing/boiling point, calculate the AT (change in temperature), then subtract that amount from the solvent s freezing point, or add it to the solvent s boiling point. 

A similar property of solutions is boiling point elevation. A solution boils at a slightly higher temperature than the pure solvent. The change in the boiling point is calculated from... 

A. 120.6°C. The problem asks for the boiling point of the solution, so you know that first you have to calculate the boiling point elevation. This means you need to know the molality of the solution and the value of the solvent (acetic acid). Table 13-2 tells you that the of acetic acid is 3.07. To calculate the molality, you must convert 45.2 g of menthol to moles ... 

The use of boiling-point elevation to determine molecular weights is based upon the same type of calculation, using KB instead of Kt. 

Values of the heat of concentration and heat capacity of sea water near room temperature have been measured experimentally. The heat of concentration values compare favorably with those calculated from the vapor pressure data given by Arons and Kientzler by use of the Clapeyron equation. The heat capacity agrees with tne values reported by Cox and Smith. Calculated values for the heat of concentration and boiling point elevation from 77° to 302° F. at salinities up to 9% are presented in both tabular and graphical form. 

Here R(T )2/A/fv ] is a property of the pure solvent. Equation (10.92) is the basic equation for the simpler expressions involving the mole fraction or molality of the solute of the equation for the boiling point elevation, but it must be emphasized that it is only an approximate equation, valid in the limit as xx approaches unity. Even for the approximation of ideal solutions, Equation (10.90) should be used for the calculation of the boiling point when Xj is removed from unity. 

Another important equation, the Gibbs-Helmholtz equation, is derived from the Maxwell relations. A chemist may use this equation to determine the enthalpy change in a reaction, and a pharmaceutical scientist may use it to calculate colligative properties (i.e., freezing point depression and boiling point elevation). The expression for free energy with respect to temperature at constant pressure is given by Equation (1.105) ... 

By taking the slope of the plot of AG/T vs. 1/T, one can determine the enthalpy change for a reaction. The equilibrium constants at different temperatures under constant pressure, freezing point depression, and boiling point elevation may be calculated from Equation (1.116), as will be discussed in Chapter 3. 

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