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Despite extensive conceptualization of ions as hard spheres in most textbooks, solid-state structures are more accurately modeled as overlapping soft spheres that better reflect the size of the ions. The corresponding soft-sphere ionic radii of alkali and halide ions can be empirically established from the partial molar volume of the ions in aqueous solution. Partial molar volumes for 15 alkali halide solutes are calculated from the slope of solution density (g/L) versus the solution molarity (mol/L) at the infinite dilution limit. The set of resulting ion sizes for the lithium, sodium, potassium, rubidium, cesium, chloride, bromide, and iodide is both self-consistent, being composed of quantities that are mathematically additive, and physically meaningful. Upon setting the volume of Li­(I) to 5.2 mL/mol, the solid-state structures of all 15 alkali halides, whether rock salt or CsCl, can be constructed to accurately model ion overlap as well as hole volume, though the size ordering of the ions is different than the ordering found for hard spheres. This new conceptual and empirical bridge between the solution and solid phases should help advance the teaching of these commonly disparate subjects by reinforcing aspects of both while drawing new connections between them.

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It is imperative to engage in interdisciplinary and multisectoral partnerships as we seek to develop and deliver effective solutions to address the global water crisis. These partnerships allow us to live out our Christian charge to demand justice for the vulnerable and promote human flourishing. This case study reviews the benefits and challenges of multisectoral partnerships between faith-based and secular organizations using the example of a multi-year water filter distribution project in Liberia. Benefits of the partnership include shared expertise, investment in students and Liberians, and results-driven research. Challenges include differing sub-goals, logistical challenges, communication difficulties, and different ways of communicating results. Intentional program planning, avoiding preferential treatment, and engagement in process evaluation are all suggestions for mitigating the potentially harmful effects of these challenges.

In Liberia, access to safe water is not universal, and waterborne diseases like diarrhea run rampant. As part of a larger border-to-border clean water project in Liberia, hollow membrane fiber filters were distributed to households in remote and/or small villages across Liberia. While filter efficacy has been demonstrated in the laboratory, studies of filter efficacy in real-world settings yield more mixed results. Intervention efficacy in Liberia was evaluated by assessing (1) user ability to correctly filter and backwash and (2) filter functioning at follow-up visits approximately 2 and 8 weeks post-intervention. Ultimately, the results supported the efficacy of this intervention. At arrival of both follow-ups, over 95% of filters were functioning properly and the majority of issues were resolved during visits. This supported the short-term durability of the filters and the importance of follow-up visits for repairs. Furthermore, the vast majority of households were able to correctly demonstrate filtering and backwashing: 88.47% at the first follow-up and 91.79% at the second. This slight increase may indicate the value of follow-up visits as educational tools. The widescale distribution of point-of-use filters as a mechanism for clean water should include on-going education and affordable filter repair and replacement opportunities.