Introduction of Differential Scanning Calorimetry in a General Chemistry Laboratory Course: Determination of Molar Mass by Freezing Point Depression

Combining Freezing Point Depression and Self-Diffusion Data for Characterizing Aggregation

“…In the case of neat cyclohexane, the liberation of heat was too fast for the instrument’s cooling control to keep a constant cooling rate, and the sample temperature actually increased slightly for a short period of time resulting in a crossover line shape for the negative cyclohexane freezing peak in Figure . However, this instrumental artifact does not impact the accuracy of the onset temperature at which the freezing phase transition begins, which for pure cyclohexane compares well with prior reported ones. , The onset temperature in Figure is reduced for a solution of 0.46 mol kg –1 biphenyl in cyclohexane by the expected amount of about 10 K based on the freezing point depression constant for cyclohexane of 20.8 K mol –1 kg . In contrast, a solution of 0.42 mol kg –1 C 10 E 6 reduces the onset temperature in Figure much less than expected by eq because of the formation of reverse micelles, which reduces the effective number of C 10 E 6 solutes.…”

“…However, this instrumental artifact does not impact the accuracy of the onset temperature at which the freezing phase transition begins, which for pure cyclohexane compares well with prior reported ones. 14,25 The onset temperature in Figure 1 is reduced for a solution of 0.46 mol kg −1 biphenyl in cyclohexane by the expected amount of about 10 K based on the freezing point depression constant for cyclohexane of 20.8 K mol −1 kg. 15 In contrast, a solution of 0.42 mol kg −1 C 10 E 6 reduces the onset temperature in Figure 1 much less than expected by eq 1 because of the formation of reverse micelles, which reduces the effective number of C 10 E 6 solutes.…”

“…Colligative properties of solutions, such as osmotic pressure, boiling point elevation, and freezing point depression, are properties that only depend on the number of dissolved solutes but not their identity. Common, longstanding chemistry laboratory curriculum experiments involve the determination of the molecular weight of nondissociable organic solutes by means of the boiling point elevation or freezing point depression, − recognizing that absolute change in phase transition temperature relative to the pure solvent, Δ T , is proportional to the solute molality, m , according to eq with K being either the molal freezing point depression or boiling point elevation constant. An underlying assumption in eq is that the solute does not aggregate, which is the case for many organic solutes in organic solvents. Conversely, solute aggregation is in principle detectable by a lesser Δ T than expected from solution molality.…”

Supporting Engagement in Metamodeling Ideas in General Chemistry: Development and Validation of Activities Designed Using Process Oriented Guided Inquiry Learning Criteria

“…Colligative properties, including vapor pressure, freezing point depression, boiling point elevation, molality, and osmotic pressure, are not focused on in the present literature, with a lack of research and educational tools and activities related to these concepts . The few published activities on colligative properties that are available for undergraduates were created for laboratory settings and analyze concepts like freezing point depression and vapor pressure. , In previously published POGIL activities related to colligative properties, students are provided equations related to boiling point elevation/freezing point depression and asked to perform calculations and draw conclusions . For our activity, emphasis was placed on guiding students to construct a definition for vapor pressure and colligative properties, along with recognizing that vapor pressure is a colligative property.…”

Evidência não evidente: as explicações em uma disciplina de química geral

“…Os químicos focalizam propriedades emergentes de sistemas que, geralmente, são muito complexos para que sejam usados modelos e métodos físicos (Brown, 2003). (Laszlo, 1998, p. 5 4 4 Os artigos selecionados foram: Josephsen, 2003;Sandi-Urena et al, 2011;Kennepohl, 2007;Walker e Sampson, 2013;Fong, 2004;D'amelia et al, 2006;D'amelia et al, 2007;D'amelia et al, 2008;Furlan e Melcer, 2014;Solow, 2004;Olsen, 2008;Kalivas, 2008;Nyasulu et al, 2013;Everest e Vargason, 2013;Lindquist et al, 2007;Griep e Mikasen, 2005;Yang e Tsai, 2006;Hansen, 1996;Blanco e Romero, 1995;Copper e Koubek, 1998;Wimpfheimer, 2004;Domin, 1999 , 2009;Martin et al, 2015;Cessna et al, 2009;Winkelmann et al, 2015;Tomasik et al, 2013;Abraham et al, 1997;Vitz e Egolf, 2002;Ni et al, 2015;Shipp et al, 2001;van Staveren et al, 2012;Silva et al, 1999;Davis et al, 2003;Bosma, 1998;Henderson e Mirafzal, 1999;Vannatta et al, 2010;Golde et al, 2006;Tic...…”