Surface Tensions of Solutions: Inputs

First, the required model is selected on the input page. The concentrations are then entered in a series of fields, and options are set using radio buttons.

• Temperature: enter an absolute temperature (in Kelvin) that is between the specified limits of 150 to 373.15 K.
• Concentration unit: the concentrations of the ions and/or NH3 can be entered either as their weight percentages in the solution, or as molalities. Note that molality is moles per kg of water, and not moles per kg of solution. Molality tends to infinity as the melt composition is approached, so weight percent is a better choice for systems at extreme concentration.
• Concentration: enter the concentration of ions and/or NH3 in the selected unit. In the former case (i.e., ion concentrations) the charge balance will be checked by the system. An error message will be shown if this test is failed.

  For the second of the two systems, concentrations can be entered for NH4⁺, OH⁻, and NH3. If entries are made for both NH4⁺ and OH⁻, the amounts will be converted to NH3 and water and a residual amount of whichever ion was in excess, using the reaction NH4⁺ + OH⁻ → NH3 + H2O. For example, if 2 mol kg⁻¹ NH4⁺ was entered, and 1 mol kg⁻¹ OH, then the NH3 concentration would be increased by 1 mol kg⁻¹ and 1 mol would be added to the total amount of water present. The remaining concentration of NH4⁺ would be 2 − 1 = 1.0 mol kg⁻¹. An analogous calculation is done in the case where weight percentages of solute species are entered rather than molalities.