Cell Notation

Clues to cocaine's toxicity could lead to better tests for its detection in biofluids

               

A new study on cocaine, the notorious white powder illegally snorted, injected or smoked by nearly 2 million Americans, details how it may permanently damage proteins in the body. That information, gleaned from laboratory tests, could be used to potentially detect the drug in biofluids for weeks or months—instead of days—after use, say scientists. The findings, which appear in the ACS journal Chemical Research in Toxicology, could also help explain cocaine's long-term health effect

cell at equilibrium

• When the cell reaction is at equilibrium, the reaction quotient Q is equal to the equilibrium constant; Q=K
• cell at equilibrium can not do work
• Potential difference, E=0

        The equilibrium constant, K, for the cell is derived using a derivative of the                                  Nernst equation:

                                                       ln K = nFE0/RT

      where F is the Faraday constant,

                  R is the gas constant, 

                  T is the temperature in kelvins.

Concentration Cell

A concentration cell is an electrolytic cell that is comprised of two half-cells with the same electrodes, but differing in concentrations. A concentration cell acts to dilute the more concentrated solution and concentrate the more dilute solution, creating a voltage as the cell reaches an equilibrium. This is achieved by transferring the electrons from the cell with the lower concentration to the cell with the higher concentration.

Problems

 Calculate cell potential for a concentration cell with two silver electrodes with concentrations 0.2M and 3.0M.

SOLUTION:

Reaction:

Ag2++2e−→Ag(s)

Cell Diagram:

Ag(s)|Ag2+(0.2M)||Ag2+(3.0M)|Ag(s)

Nernst Equation:

E=Eo−0.05922log 0.23.0

  **Eo = 0 for concentration cells

                       E = 0.0644V

Nernst Equation

Related the zero current potential to the activities of the participants in the cell reaction

                   (half-cell reduction potential)

           

                  (total cell potential) (Q)- Reaction Quotient

liquid junction potential

• In a cell when two different electrolytes are in contact, an additional source of potential difference occur across the interface of the two electrolytes  
• That is called liquid junction potential

Isomerism in Coordination Compounds

                                Isomerism in Coordination Compounds

Isomers are two or more compounds that have the same chemical formula but a different arrangement of atoms. Because of the different arrangement of atoms, they differ in one or more physical or chemical properties. Two principal types of isomerism are known among coordination compounds. Each of which can be further subdivided. 

(a) Stereoisomerism

               (i) Geometrical isomerism           (ii) Optical isomerism

 (b) Structural isomerism

                 (i) Linkage isomerism                 (ii) Coordination isomerism                                                                 (iii) Ionisation isomerism             (iv) Solvate isomerism 

Stereoisomers have the same chemical formula and chemical bonds but they have different spatial arrangement. Structural isomers have different bonds. A detailed account of these isomers are given below.

•   Geometric Isomerism

                The facial (fac) and meridional (mer) isomers of [Co(NH3 )3(NO2 )3]

Naming organic chemistry compounds

The chemistry of carbon compounds

Introduction to Spectroscopy

In previous sections of this text the structural formulas of hundreds of organic compounds have been reported, often with very little supporting evidence. These structures, and millions of others described in the scientific literature, are in fact based upon sound experimental evidence, which was omitted at the time in order to focus on other aspects of the subject. Much of the most compelling evidence for structure comes from spectroscopic experiments, as will be demonstrated in the following topics. The Light of Knowledge is an often used phrase, but it is particularly appropriate in reference to spectroscopy. Most of what we know about the structure of atoms and molecules comes from studying their interaction with light (electromagnetic radiation). Different regions of the electromagnetic spectrum provide different kinds of information as a result of such interactions. Realizing that light may be considered to have both wave-like and particle-like characteristics, it is useful to consider that a given frequency or wavelength of light is associated with a "light quanta" of energy we now call a photon. As noted in the following equations, frequency and energy change proportionally, but wavelength has an inverse relationship to these quantities. In order to "see" a molecule, we must use light having a wavelength smaller than the molecule itself (roughly 1 to 15 angstrom units). Such radiation is found in the X-ray region of the spectrum, and the field of X-ray crystallography yields remarkably detailed pictures of molecular structures amenable to examination. The chief limiting factor here is the need for high quality crystals of the compound being studied. The methods of X-ray crystallography are too complex to be described here; nevertheless, as automatic instrumentation and data handling techniques improve, it will undoubtedly prove to be the procedure of choice for structure determination. The spectroscopic techniques described below do not provide a three-dimensional picture of a molecule, but instead yield information about certain characteristic features. A brief summary of this information follows: • Mass Spectrometry: Sample molecules are ionized by high energy electrons. The mass to charge ratio of these ions is measured very accurately by electrostatic acceleration and magnetic field perturbation, providing a precise molecular weight. Ion fragmentation patterns may be related to the structure of the molecular ion. • Ultraviolet-Visible Spectroscopy: Absorption of this relatively high-energy light causes electronic excitation. The easily accessible part of this region (wavelengths of 200 to 800 nm) shows absorption only if conjugated pi-electron systems are present. • Infrared Spectroscopy: Absorption of this lower energy radiation causes vibrational and rotational excitation of groups of atoms. within the molecule. Because of their characteristic absorptions identification of functional groups is easily accomplished. • Nuclear Magnetic Resonance Spectroscopy: Absorption in the low-energy radio-frequency part of the spectrum causes excitation of nuclear spin states. NMR spectrometers are tuned to certain nuclei (e.g. 1H, 13C, 19F & 31P). For a given type of nucleus, high-resolution spectroscopy distinguishes and counts atoms in different locations in the molecule.

What Is Chemistry?

Chemistry is the study of matter and energy and the interactions between them. This is also the definition for physics, by the way. Chemistry and physics are specializations of physical science. Chemistry tends to focus on the properties of substances and the interactions between different types of matter, particularly reactions that involve electrons. Physics tends to focus more on the nuclear part of the atom, as well as the subatomic realm. Really, they are two sides of the same coin.