B555`S CHEMISTRY HUB

OIL AND WATER CAN FORM A STABLE DISPERSION WITH THE HELP OF A THIRD SUBSTANCE .WHAT IS THAT SUBSTANCE?

Composition of a sample of wustite is Fe0.93 .What percentage of iron is present in the form of Fe(III)

When a bottle of perume is opened, odorous molecules mix with air and slowly diffuse throughout the entire room. which is correct for this process ?

a) G<0
b) S>0
c) H nearly equal to 0
d) S<0

1 mole of Fe0.9 O was dopped by 0.2 mole Ti4+ ions where Ti4+ replaced Fe+2 replaced Fe+2 in the crystal. this compound is dissolved in 1 litre of water & ten treated with 0.1N KMnO4 SOLUTION IN ACIDIC MEDIUM. calculate volume of KMnO4 required in ml

1]how larger anions are stabilised by larger cations through lattice energy effects.....is the reason dat superoxide ion o2- is stabilised by large cations like potassium,rubidium...

2]Expain the trend of boiling point & melting point BF3

3) dIAMOND HAVE BETTER THERMAL CONDUCTIVITY THAN Cu. Why?

4]Is WO4 4- a better oxidizing agent than CrO4 4- if yes or no also give me the parameters for measuring the strength of oxidizing agent!!!!

Catalysts
With rare exception, no reaction below 480 °C occurs between H2 and organic compounds in the absence of metal catalysts. The catalyst binds both the H2 and the unsaturated substrate and facilitates their union. Platinum group metals, particularly platinum, palladium, rhodium, and ruthenium, form highly active catalysts, which operate at lower temperatures and lower pressures of H2. Non-precious metal catalysts, especially those based on nickel (such as Raney nickel and Urushibara nickel) have also been developed as economical alternatives, but they are often slower or require higher temperatures. The trade-off is activity (speed of reaction) vs. cost of the catalyst and cost of the apparatus required for use of high pressures. Notice that the Raney-nickel catalysed hydrogenations require high pressures:[4][5]

Two broad families of catalysts are known - homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts dissolve in the solvent that contains the unsaturated substrate. Heterogeneous catalysts are solids that are suspended in the same solvent with the substrate or are treated with gaseous substrate.

[edit] Homogeneous catalysts
Illustrative homogeneous catalysts include the rhodium-based compound known as Wilkinson's catalyst and the iridium-based Crabtree's catalyst. An example is the hydrogenation of carvone: [6].

Hydrogenation is sensitive to steric hindrance explaining the selectivity for reaction with the exocyclic double bond but not the internal double bond.

The activity and selectivity of homogeneous catalysts is adjusted by changing the ligands. For prochiral substrates, the selectivity of the catalyst can be adjusted such that one enantiomeric product is favored. Asymmetric hydrogenation is also possible via heterogeneous catalysis on a metal that is modified by a chiral ligand.[7]

Homogeneous catalysts are less active than heterogeneous catalysts.

[edit] Heterogeneous catalysts
Heterogeneous catalysts for hydrogenation are more common industrially. As in homogeneous catalysts, the activity is adjusted through changes in the environment around the metal, i.e. the coordination sphere. Different faces of a crystalline heterogeneous catalyst display distinct activities, for example. Similarly, heterogeneous catalysts are affected by their supports, i.e. the material upon with the heterogeneous catalyst is bound. In many cases, highly empirical modifications involve selective "poisons." Thus, a carefully chosen catalyst can be used to hydrogenate some functional groups without affecting others, such as the hydrogenation of alkenes without touching aromatic rings, or the selective hydrogenation of alkynes to alkenes using Lindlar's catalyst. For example, when the catalyst palladium is placed on barium sulfate and then treated with quinoline, the resulting catalyst reduces alkynes only as far as alkenes. The Lindlar catalyst has been applied to the conversion of phenylacetylene to styrene.[8]

Asymmetric hydrogenation is also possible via heterogeneous catalysis on a metal that is modified by a chiral ligand.[7]

[edit] Hydrogen sources
For hydrogenation, the obvious source of hydrogen is H2 gas itself, which is typically available commercially within the storage medium of a pressurized cylinder. The hydrogenation process often uses greater than 1 atmosphere of H2, usually conveyed from the cylinders and sometimes augmented by "booster pumps". Gaseous hydrogen is produced industrially from hydrocarbons by the process known as steam reforming.[9]

Hydrogen may, in specialised applications, also be extracted ("transferred") from "hydrogen-donors" in place of H2 gas. Hydrogen donors, which often serve as solvents include hydrazine, dihydronaphthalene, dihydroanthracene, isopropanol, and formic acid.[10] In organic synthesis, transfer hydrogenation is useful for the reduction of polar unsaturated substrates, such as ketones, aldehydes, and imines

well note the date in right coloumn of the previos post.!!!!!!!!!!!!!!

some one try the beech waale questions na....................

@ bhargav
yaar Q5 mein fugicity hai ya fugacity [7]
vaise fugacity ka wiki pe kuch mila tha

Fugacity is a measure of a chemical potential in the form of 'adjusted pressure.' It reflects the tendency of a substance to prefer one phase (liquid, solid, or gas) over another, and can be literally defined as “the tendency to flee or escape”. At a fixed temperature and pressure, a homogeneous substance will have a different fugacity for each phase. The phase with the lowest fugacity will be the most favorable, and will have the lowest Gibbs free energy. Fugacity has the same units as pressure (e.g., atm, psia, bars, etc.)

contd..........
Q2
In the boron trihalides, BX3, the length of the B-F bonds (1.30 Ã
) is shorter than would be expected for single bonds, and this shortness may indicate stronger B-X π-bonding in the fluoride. A facile explanation invokes the symmetry-allowed overlap of a p orbital on the boron atom with the in-phase combination of the three similarly oriented p orbitals on fluorine atoms.

I HOPE THIS WILL MAKE MATTER MORE CLEAR