Studies of concentrated electrolyte solutions using the electrodynamic balance. 1. Water activities for single-electrolyte solutions

Abstract

An electrodynamic balance apparatus has been used to suspend single, 20-#tm-diameter, charged droplets of aqueous salt solutions in a humid environment. From measurements of the humidity surrounding the droplet and the relative mass of the particle in its wet and dry states, the dependence of water activity on solute concentration was determined for aqueous solutions of the following salts at 20 °C: NaCl, NaBr, KC1, KBr, NH4C1, Na2S04, (NH4)2S04, CaCl2, MnCl2, and FeCl3. This technique allowed the thermodynamics of highly supersaturated solutions to be studied, and for most of the salts, the measurements were made to higher concentrations than have previously been reported at comparable temperatures. The dependence of the solute activity coefficient on concentration was calculated for each of the salts, and the features of this dependence are discussed in relationship to ionic hydration and association. Several semiempirical electrolyte solution models were tested against the data, and it was found that salt-specific model parameters estimated from low-concentration data could not be reliably used to predict the solution behavior at high concentrations. However, with estimated parameters based on the full range of the data, the models were able to represent the experimental data to within the uncertainty in the measurements.

Canadian Aerosol Module: A size‐segregated simulation of atmospheric aerosol processes for climate and air quality models 1. Module development

“…[13] There exist several methods to estimate the water uptake by mixed soluble aerosols [Cohen et al, 1987a[Cohen et al, , 1987bSaxena and Peterson, 1981]. The so-called ZSR (Zdandovskii-Stokes-Robinson) method [Sangster et al, 1973;Stokes and Robinson, 1966] has been used in treating multicomponent aerosol solutions.…”

Determination of Water Activity in Ammonium Sulfate and Sulfuric Acid Mixtures Using Levitated Single Particles

“…en previously (Cohen et al, 1987a;Chan et al, 1992). A charged droplet is trapped in the SVEL by controlling the a.c. field, and the d.c. field is then adjusted to balance the weight of the particle.…”

“…If these values agree within a reasonable range, the aforementioned assumption is deemed to be a reasonable one and the mfs based on the dry particle assumption is used. This is the approach followed by Cohen et al (1987a). If that is not the case, we follow the approach adopted by Chan et al (1992) in estimating solution concentration.…”

“…An advantage of the levitated single particle techniques is that the exact mass change of a droplet can be measured. These techniques have been widely used to study solution thermodynamics and chemistry of single component solutions Munkelwitz, 1977, 1984;Rubel, 1981;Richardson and Kurtz, 1984;Richardson and Spann, 1984;Tang et al, 1986;Cohen et al, 1987a;Chan et al, 1992) and multicomponent solutions (Tang et al, 1978;Spann and Richardson, 1985;Cohen et a]., 1987b;Chan et al, 1992).…”

Water Content and Phase Transitions in Particles of Inorganic and Organic Species and their Mixtures Using Micro-Raman Spectroscopy

“…The electrodynamic balance (EDB) (Richardson and Spann 1984;Cohen et al 1987;Tang et al 1995) and humidified tandem differential mobility analyzer (HTDMA) (McMurry and Stolzenburg 1989;Svenningsson et al 1997;Chan and Chan 2005;Swietlicki et al 2008) have been widely used to study the hygroscopic growth of suspended particles. However, these techniques give no direct information of the phase state of the particles' components.…”