SUNAYANA

  1. In the determination of Ca with AAS, interferences occur due to formation of refractory oxides CaO.P2O5 and Cao.SiO3. It can be eliminated by  a. Changing air acetylene flame to nitrous oxide acetylene flame b. Decreasing oxygen concentration c. Adding of a releasing agent d. using fuel rich flame 1. a and b only             2. aand c        3.a and d        4. a,b,c and d 2. Iron (III) is best determined by UV-visible spectroscopy with 1 . Thiocyanate      2. Acetate     3. Cyanide    4. Dimethylglyoxime 3 . In the AAS, Ne+ gaseous ions bombarded the cathode ( Hollow cathode Lamp) and eject metal atoms from cathode , The process is referred to as 1. Sputtering    2. Ejectioning    3. Excitation   4. Ionisation 4 . Moment of nuclei is negligible during the time taken by an electronic transition . It is called  1. Frank ...

INTRODUCTION: Coulometry is a dynamic techniques in analytical chemistry which determines the amount of matter transformed during an electrolysis reaction by  measuring an unknown concentration of an analyte in solution and completely converting the analyte from one oxidation state to another. It  is an absolute measurement similar to gravimetry or titration and requires no chemical standards or calibration . Figure: Schematic of a coulometric cell Coulometric Titration There are two basic categories of coulometry: - 1.       Controlled potential coulometry or Potentiostatic coulometry 2.       Controlled-current coulometry or amperostatic coulometry These coulometric methods can be classified in following categories: - 1.       Potentiostatic coulometry: Potentiostatic coulometry technique is  most commonly referred to as bulk electrolysis . Here the working electrode is kept at a con...

  Introduction   The scanning Tunneling Microscope(STM) was invented in the early 1980s by Binning and Rohrer who were awarded the 1986 Nobel Prize in Physics. In Scanning Tunneling Microscopy(STM), a sharp metal tip (W, Pt–Ir) is brought sufficiently close to proximity of a conducting sample, and a bias is applied, so that their electron-wave functions can overlap and electrons tunnel between the two. Fig: Schematic diagram of STM instrument The working of STM   In STM once the gap between the tip and sample is about as small as the diameter of an atom, a tunnelling current flows in the range of pico and nano amperes. The magnitude of the current is very sensitive to the size of the gap, changing by a factor of 10 when the distance changes by 100 pm. The metal tip is scanned backward and forward across the solid, and the steep variation of the tunneling current with distance gives an image of the atoms on the surface. The image is usually formed by keeping a c...

  Introduction Atomic force microscopy or AFM is similar to STM relies on a very sharp tip, but in this case, the tip is brought close enough to the surface that the intermolecular forces between tip and   the surface can be measured. It is a method to see a surface in its full, three-dimensional picture, down to the nanometer scale. This method applies to hard and soft synthetic materials as well as biological structures (tissues, cells, biomolecules), irrespective of opaqueness or conductivity.   Working of AFM AFM provides a 3D profile of the surface on a nanoscale, by measuring forces between a sharp probe (<10 nm) and surface at very short distance (0.2-10 nm probe-sample separation). The probe is supported on a flexible cantilever. The AFM tip gently touches the surface and records the small force between the probe and the surface. Most commonly, the sharp tip is attached to a flexible microcantilever – essentially a microscopic diving board – which bends...

  Radioactivity of Lanthanides and Actinides Radioactivity Radioactivity is the extra energy, or radiation, emitted by  radioactive  elements that comes in three different types: alpha, beta, and gamma. Alpha radiation is a stream of alpha particles, which are positively charged. They're fairly large, which means they have a difficult time getting through materials like clothes and paper. Lanthanide and  Actinide  Series are both referred to as Rare Earth Metals. Both actinides and  lanthanides  are highly reactive with elements from the halogen group. Radioactivity of lanthanides The  lanthanide  series includes elements 58 to 71, which fill their 4f sublevel progressively. The  lanthanide  series can be found naturally on Earth. In the lanthanide series only radioactive elements are promethium and samarium. All of the  lanthanides  have at least one stable isotope except for promethium. Promethium being radioact...

  APPLICATIONS OF CRYSTAL FIELD THEORY Crystal field theory was developed by Hans Bethe(1929) and Van Vleck(1935). This theory ( CFT ) largely replaced Valence Bond Theory for interpreting the chemistry of coordination compounds. Main assumptions in CFT, ·          According to CFT, the interactions between the central metal ion and its ligands are purely electrostatic (ionic). ·          The ligands are treated as point Charges. ·          If the ligand is anionic : ion-ion interaction. If the ligand is neutral : ion-dipole interaction ·          The electrons on metal occupy those d-orbitals farthest away from the direction of approach of ligands. Three p - orbitals Five d - orbitals In octahedral field: dxy, dxz, dyz ▬ t 2g set dz², dx²-y² ▬ e g set Applications of CFT are, 1.    ...