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Molar, Third: The aftermost permanent tooth on each side in the maxilla and mandible.
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Freezing-Point Depression to Determine an Unknown Compound

JoVE 10137

Source: Laboratory of Lynne O' Connell — Boston College

When a solid compound is dissolved in a solvent, the freezing point of the resulting solution is lower than that of the pure solvent. This phenomenon is known as freezing-point depression, and the change in temperature is directly related to the molecular weight of the solute. This experiment is designed to find the identity of an unknown compound by using the phenomenon of freezing-point depression to determine its molecular weight. The compound will be dissolved in cyclohexane, and the freezing point of this solution, as well as that of pure cyclohexane, will be measured. The difference between these two temperatures allows for the calculation of the molecular weight of the unknown substance.


 General Chemistry

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Spectrophotometric Determination of an Equilibrium Constant

JoVE 10094

Source: Laboratory of Dr. Michael Evans — Georgia Institute of Technology

The equilibrium constant, K, for a chemical system is the ratio of product concentrations to reactant concentrations at equilibrium, each raised to the power of their respective stoichiometric coefficients. Measurement of K involves determination of these concentrations for systems in chemical equilibrium. Reaction systems containing a single colored component can be studied spectrophotometrically. The relation between absorbance and concentration for the colored component is measured and used to determine its concentration in the reaction system of interest. Concentrations of the colorless components can be calculated indirectly using the balanced chemical equation and the measured concentration of the colored component. In this video, the Beer's law curve for Fe(SCN)2+ is determined empirically and applied to the measurement of K for the following reaction: Four reaction systems with different initial concentrations of reactants are investigated to illustrate that K remains constant irrespective of initial concentration


 General Chemistry

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Introduction to Titration

JoVE 5699

Source: Laboratory of Dr. Yee Nee Tan — Agency for Science, Technology, and Research

Titration is a common technique used to quantitatively determine the unknown concentration of an identified analyte.1-4 It is also called volumetric analysis, as the measurement of volumes is critical in titration. There are many types of titrations based on the types of reactions they exploit. The most common types are acid-base titrations and redox titrations.5-11 In a typical titration process, a standard solution of titrant in a burette is gradually applied to react with an analyte with an unknown concentration in an Erlenmeyer flask. For acid-base titration, a pH indicator is usually added in the analyte solution to indicate the endpoint of titration.12 Instead of adding pH indicators, pH can also be monitored using a pH meter during a titration process and the endpoint is determined graphically from a pH titration curve. The volume of titrant recorded at the endpoint can be used to calculate the concentration of the analyte based on the reaction stoichiometry. For the acid-base titration presented in this video, the titrant is a standardized sodium hydroxide solution and the analyte is domestic vinegar. Vinegar is an acidic liquid that


 General Chemistry

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Evaluating the Accuracy of Snap Judgments

JoVE 10309

Source: Diego Reinero & Jay Van Bavel—New York University

Social psychologists have long been interested in the way people form impressions of others. Much of this work has focused on the errors people make in judging others, such as the exaggerated influence of central traits (such as "warm" and "cold"), the insufficient weight given to the context in which others' behavior takes place, and the tendency for people to make judgments that conform to their initial expectations about another. However, this focus on errors masks the fact that people are quite good at making fairly accurate judgments about other people's characteristics, an ability that was no doubt important over the course of human evolution. Indeed, the human ability to make quick sense of social situations and people ranks among our most valuable skills. What is particularly impressive about our ability to make sense of others is not just how little information we need to make inferences, but how well calibrated we can be with so little information. This video shows some experimental techniques used by psychology researchers, including Ambady and Rosenthal in their seminal work,1 and explores the process of making inferences in the context of students' evaluati


 Social Psychology

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Streamlined Single Cell TCR Isolation and Generation of Retroviral Vectors for In Vitro and In Vivo Expression of Human TCRs

1Department of Pediatrics, Section of Diabetes and Endocrinology, McNair Medical Institute, Baylor College of Medicine, Texas Children's Hospital, 2Benaroya Research Institute at Virginia Mason, 3Center for Human Immunobiology, Baylor College of Medicine, Texas Children's Hospital, 4Department of Pediatrics, Section of Diabetes and Endocrinology, Baylor College of Medicine, Texas Children's Hospital

JoVE 55379


 Immunology and Infection

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Micro-Dissection of Enamel Organ from Mandibular Incisor of Rats Exposed to Environmental Toxicants

1Institut National de la Santé et Recherche Médicale (INSERM) UMRS 1138, Paris-Diderot University, Pierre & Marie Curie University, Paris-Descartes University, Laboratory of Molecular Oral Pathophysiology, Cordeliers Research Centre, 2Unit of Formation and Research (UFR) of Odontology, Paris-Diderot University

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JoVE 57081


 JoVE In-Press

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