Water vapor partial pressure of ammonium salt solution
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A mixed solution of ammonium salts, with the following composition: ammonium thiocyanate, 150 g/L; ammonium thiosulfate, 100 g/L; water, 850 g/L. How can I calculate or find the saturated vapor pressure of this mixed solution at 30°C and 120 KPaA?
To calculate the saturated vapor pressure of an ammonium salt solution at 30°C and 120 KPaA, Raoult’s law can be used. According to Raoult’s law, the saturated vapor pressure of a mixed solution is equal to the sum of the products of the mole fractions of each component and their respective vapor pressures. First, it is necessary to calculate the mole fractions of ammonium thiocyanate, ammonium thiosulfate, and water. The molar mass of ammonium thiocyanate is 1 sulfur atom + 1 carbon atom + 2 nitrogen atoms + 4 hydrogen atoms + 1 ammonium ion = 55.5 g/mol. Therefore, the molar fraction of ammonium thiocyanate = mass of ammonium thiocyanate (g) / total mass of the solution (g) = (150 g/L) / (150 g/L + 100 g/L + 850 g/L) = 0.150. The molar mass of ammonium thiosulfate is 1 sulfur atom + 3 hydrogen atoms + 1 ammonium ion = 76 g/mol. Therefore, the molar fraction of ammonium thiosulfate = mass of ammonium thiosulfate (g) / total mass of the solution (g) = (100 g/L) / (150 g/L + 100 g/L + 850 g/L) = 0.100. The molar mass of water is 2 hydrogen atoms + 1 oxygen atom = 18 g/mol. Therefore, the molar fraction of water = mass of water (g) / total mass of the solution (g) = (850 g/L) / (150 g/L + 100 g/L + 850 g/L) = 0.850. Then, it is necessary to look up the vapor pressures of each component at 30°C. You can consult relevant materials or use a database of material properties. Finally, by adding the products of the molar fractions of each component and their corresponding vapor pressures, the saturated water vapor pressure of the ammonium salt solution at 30°C and 120 KPaA can be obtained. .
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Thank you very much for your advice. At first, I also wanted to use Lame’s law for the calculation. However, Raoult’s law applies to ideal dilute solutions and does not apply to this ammonium salt solution, right? It should work for approximate calculations.