Molality, aqueous solutions

A 1.00 molal aqueous solution of trichloroacetic acid (CCl3COOH) is heated to the boiling point. The solution has a boiling point of 100.18°C. 

A 5.2 molal aqueous solution of methyl alcohol, CH3OH, is supplied. What is the mole fraction of methyl alcohol in this solution ... 

An infinitesimal transfer of glycine from the sohd phase to the solution at constant temperature, pressure, and composition of solution results in a corresponding change dJ in the thermodynamic property J of the system composed of crystalline glycine and a 1-molal aqueous solution of glycine. The application of Equation (9.32) leads to the expression... 

A 0 0200 molal aqueous solution of picric acid, HCbH207N3, freezes al -0 0656°C Picric acid ionizes to a certain extent in water, as... 

From AGf° for CH30H(1) and ideal solution correction to 1 molal aqueous solution. 

Problem An exactly 1 molal aqueous solution of mannitol has a vapor pressure of 17.222 mm. of mercury at 20° C at the same temperature, tlie vapor pressure of pure water is 17.535 mm. Calculate tlie activity and activity coefficient of water in the given solution. 

A molal aqueous solution contains 1 mole of solute and 1000/18.016 = 55.51 moles of solvent the mole fraction of solvent is thus... 

The activity and mole fraction are so close that the activity coefficient is virtually unity. (It is of interest to note that the mole fraction N2 of the solute in a 1 molal aqueous solution is only 1.0000 — 0.9823 = 0.0177, and so it is not surprising to find that the solvent obeys Raoult s law.)... 

Calculate the effective radius of the ionic atmosphere (l/x) in a 0.1 molal aqueous solution of potassium sulfate at 25 C. The dielectric constant of water at 26 C is 78.64. 

As we have emphasized, colligative properties depend on the number of solute particles in a given mass of solvent. A 0.100 molal aqueous solution of a covalent compound that does not ionize gives a freezing point depression of 0.186°C. If dissociation were complete, 0.100 m KBr would have an ejfective molality of 0.200 m (i.e., 0.100 m K+ + 0.100 m Br ). So we might predict that a 0.100 molal solution of this 1 1 strong electrolyte would have a freezing point depression of 2 X 0.186°C, or 0.372°C. In fact, the observed depression is only 0.349°C. This value for ATf is about 6% less than we would expect for an effective molarity of 0.200 m. 

Predict the mean activity coefficient of Na2S04 in a 1.5 molal aqueous solution at 298.15 K using the LIQUAC model. For the calculation the following properties should be used ... 

Calculate the mole fractions of all true species in a 0.1 molal aqueous solution of sodium thiosulfate assuming complete dissociation. Is this a valid assumption. ... 

A laboratory procedure calls for a 2.0 molal aqueous solution. A student accidentally makes a 2.0 molar solution. The solution made by the student is ... 

The mean ionic activity coefficient of NaCl in a 0.100 molal aqueous solution at 298.15K has been evaluated with measurements of equilibrium cell potentials," with the result In y = —0.2505. Use this value in Eq. 10.6.9, together with the values of osmotic coefficients in Table 10.1, to evaluate y at each of the molalities shown in the table then plot y as a function of wb. 

Freezing-point depression. A 0.00200 molal aqueous solution of KCo(NH3)2(N02)4 fieezes at —0.00736 C. How many moles of ions are present in a dilute solution containing 1 mole of this compound ... 

Freezing-point depression. Estimate the freezing point of a 0.01000 molal aqueous solution of KCIO3, an ionic salt. 

A 200,000-amu average molecular weight polymer is contaminated with 0.5% of a 100-amu impurity, presumably the monomer. Determine the error in the molecular weight determination if a 1.000 x lO molal aqueous solution is used. Assume a temperature of 25.0°C. 

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