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Molar, Third: The aftermost permanent tooth on each side in the maxilla and mandible.
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 Science Education: Essentials of General Chemistry

Freezing-Point Depression to Determine an Unknown Compound

JoVE Science Education

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.

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 JoVE Bioengineering

In situ Compressive Loading and Correlative Noninvasive Imaging of the Bone-periodontal Ligament-tooth Fibrous Joint

1Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, University of California San Francisco, 2Department of Radiology and Biomedical Imaging, University of California San Francisco, 3Xradia Inc.


JoVE 51147

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 Science Education: Essentials of General Chemistry

Introduction to Titration

JoVE Science Education

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

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 Science Education: Essentials of General Chemistry

Spectrophotometric Determination of an Equilibrium Constant

JoVE Science Education

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

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 Science Education: Essentials of General Chemistry

Determining the Empirical Formula

JoVE Science Education

Source: Laboratory of Dr. Neal Abrams - SUNY College of Environmental Science and Forestry

Determining the chemical formula of a compound is at the heart of what chemists do in the laboratory every day. Many tools are available to aid in this determination, but one of the simplest (and most accurate) is the determination of the empirical formula. Why is this useful? Because of the law of conservation of mass, any reaction can be followed gravimetrically, or by change in mass. The empirical formula provides the smallest whole-number ratio among elements (or compounds) within a molecular compound. In this experiment, gravimetric analysis will be used to determine the empirical formula of copper chloride hydrate, CuxCly·nH2O.

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 Science Education: Essentials of Analytical Chemistry

Ultraviolet-Visible (UV-Vis) Spectroscopy

JoVE Science Education

Source: Laboratory of Dr. B. Jill Venton - University of Virginia

Ultraviolet-visible (UV-Vis) spectroscopy is one of the most popular analytical techniques because it is very versatile and able to detect nearly every molecule. With UV-Vis spectroscopy, the UV-Vis light is passed through a sample and the transmittance of light by a sample is measured. From the transmittance (T), the absorbance can be calculated as A=-log (T). An absorbance spectrum is obtained that shows the absorbance of a compound at different wavelengths. The amount of absorbance at any wavelength is due to the chemical structure of the molecule. UV-Vis can be used in a qualitative manner, to identify functional groups or confirm the identity of a compound by matching the absorbance spectrum. It can also be used in a quantitative manner, as concentration of the analyte is related to the absorbance using Beer's Law. UV-Vis spectroscopy is used to quantify the amount of DNA or protein in a sample, for water analysis, and as a detector for many types of chromatography. Kinetics of chemical reactions are also measured with UV-Vis spectroscopy by taking repeated UV-Vis measurements over time. UV-Vis measurements are generally taken with a spectrophotometer. UV-Vis is also a very popular detector for other analytical tech

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 JoVE Behavior

Examination of Rapid Dopamine Dynamics with Fast Scan Cyclic Voltammetry During Intra-oral Tastant Administration in Awake Rats

1Interdepartmental Neuroscience Program, Yale University, 2Department of Biotechnical and Clinical Laboratory Sciences, School of Medicine and Biomedical Sciences, University at Buffalo, 3Department of Psychiatry, Yale School of Medicine, 4Department of Cellular and Molecular Physiology, Yale School of Medicine


JoVE 52468

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 JoVE Bioengineering

Fully Automated Centrifugal Microfluidic Device for Ultrasensitive Protein Detection from Whole Blood

1Department of Biomedical Engineering, School of Life Sciences, Ulsan National Institute of Science and Technology (UNIST), UNIST-gil 50, Ulsan, Republic of Korea, 2Current Affiliation is Agency for Defense Development (ADD), Daejeon, Republic of Korea, 3Current Affiliation is KOGAS (Korea Gas Corporation) Research Institute, Daegu, Republic of Korea, 4Center for Soft and Living Matter, Institute for Basic Science (IBS), UNIST-gil 50, Ulsan, Republic of Korea


JoVE 54143

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