Chemistry Is My Passion

09/08/2016

05/06/2016

😉

05/06/2016

Yes

05/06/2016

Did you know?

05/06/2016

POLARIMETER:

This is one of the most crucial analytical instruments in organic chemistry, particularly . The instrument works on the principle of of plane of polarized light by optically active chiral molecules.

An organic molecule with stereocencter or chiral center is capable of rotating plane of polarized light to produce a mirror image with which it's not superposable. Such stereoisomers are called . Sample is placed in the sample tube and the light is set from the source. The rotation is observed on the field of view in the instrument.

A rotation of the light on the clockwise direction indicates a (-) isomers while rotation in the counterclockwise (right) direction indicates (+) isomers. If the samples are not mirror images, they are said to be . A mixture of Stereoisomers of equal molar concentration (uquimolar) are termed as .

NB: enantiomers are the same hence have similar physical and chemical properties. However, diastereomers are not the same and cannot be used interchangeably.
Connect for more information.

25/05/2014

Colour of lanthanide compounds
The lanthanide metals are silvery white but the tivalent lanthanide ions show different colours.
Colour of the ions depend on the number of unpaired electrons because the elements with (x)f electrons often have a similar colour to those of (14-x)f electrons.
No. of unpaired electrons Ions colour
0 La3+, Lu3+ Colourless
1 Ce3+, Yb3+ Colourless
2 Pr3+, Tm3+ Green
3 Nd3+, Er3+ Red
4 Pm3+, Ho3+ Pink and Yellow respectively
5 Sm3+, Dm3+ Yellow
6 Eu3+, Tb3+ Pink
7 Gd3+ Colourless
The colour of lanthanide ions is due to the presence of partly filled f orbitals. As a result it is possible to absorb certain wavelength from the visible region of the spectrum. This results in transitions from one 4f orbital to another 4f orbital known as f-f transition..

04/01/2014

Le Chatelier's Principle ► ► ►
► A statement of Le Chatelier's Principle
• If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.
1. Effect of Concentration

A + 2B C + D

If increase the concentration of A, equilibrium position will shift to the forward direction in order to maintain the balance of A.

Suppose you want to convert B into C and D but it’s a expensive material whereas A is cheap material. This way is the low cost way to produce C and D from minimum amount of A

2. Effect of Pressure

A(g) + 2B(g) C(g) + D(g)

Pressure is caused by gas molecules hitting the sides of their container.

Therefore, increasing the pressure on a gas reaction shifts the position of equilibrium towards the side with fewer molecules in order to decrease the pressure.

Decreasing the pressure on a gas reaction shifts the position of equilibrium backwards the side with higher molecules in order to increase the pressure.

But there is another case, what will happen if the number of molecules is same at both sides of the equilibrium equation.

In this case, no effect occurred by the pressure change.

3. Effect of temperature

If the forward reaction is exothermic (heat is evolved):

A + 2B C + D ; ΔH = -250 kJ/mol

250 kJ evolved when A and 2B completely react to give C and D, and 250 kJ absorbed when C and D react completely to give A and 2B.

If the temperature is increased, the system needs to decrease the temperature; it needs to cool itself hence it should absorb extra heat. So endothermic reaction is taken place.

And if the temperature is decreased, the system needs to increase the temperature; it needs to heat itself hence it should evolve heat, so exothermic reaction is taken place.

# Adding a catalyst makes absolutely no difference to the position of equilibrium, and Le Chatelier's Principle doesn't apply to them.

Because of, a catalyst speeds up the forward and back reaction to the same extent.

Because adding a catalyst doesn't affect the relative rates of the two reactions, it can't affect the position of equilibrium.

A catalyst is used because of it speeds up the rate at which a reaction reaches dynamic equilibrium. If not, for slow reactions, it could take months or years of time.

04/01/2014

Extracting iron from iron ore using a Blast Furnace

Introduction
The common ores of iron are both iron oxides, and these can be reduced to iron by heating them with carbon in the form of coke.

Coke is produced by heating coal in the absence of air.

Coke is cheap and provides both the reducing agent for the reaction and also the heat source

Iron ores
The most commonly used iron ores are
haematite (US: hematite) - Fe2O3
magnetite - Fe3O4.

The Blast Furnace used in here is shown in figure 01

The heat source
The air blown into the bottom of the furnace is heated using the hot waste gases from the top.
Heat energy is valuable, and it is important not to waste any.
The coke (essentially impure carbon) burns in the blast of hot air to form carbon dioxide - a strongly exothermic reaction.

This reaction is the main source of heat in the furnace.

C + O2 --------------- > CO2

The reduction of the ore
At the high temperature at the bottom of the furnace, carbon dioxide reacts with carbon to produce carbon monoxide.
C + CO2 ------- > 2CO

It is the carbon monoxide which is the main reducing agent in the furnace.

Fe2O3 + 3CO --------- > 2Fe + 3CO2

In the hotter parts of the furnace, the carbon itself also acts as a reducing agent.

*Notice that at these temperatures, the other product of the reaction is carbon monoxide, not carbon dioxide.
Fe2O3 +3C ----------- > 2Fe + 3CO

The temperature of the furnace is hot enough to melt the iron which trickles down to the bottom where it can be tapped off.
The function of the limestone
Iron ore isn't pure iron oxide , it also contains an assortment of rocky material.

This wouldn't melt at the temperature of the furnace, and would eventually clog it up.

The limestone is added to convert this into slag which melts and runs to the bottom.

The heat of the furnace decomposes the limestone to give calcium oxide.
CaCO3 --------------- > CaO + CO2

This is an endothermic reaction, absorbing heat from the furnace.

It is therefore important not to add too much limestone because it would otherwise cool the furnace.

Calcium oxide is a basic oxide and reacts with acidic oxides such as silicon dioxide present in the rock.

Calcium oxide reacts with silicon dioxide to give calcium silicate.
CaO + SiO2------------ > CaSiO3

The calcium silicate melts and runs down through the furnace to form a layer on top of the molten iron. It can be tapped off from time to time as slag.

Slag is used in road making and as "slag cement" , a final ground slag which can be used in cement, often mixed with Portland cement.

Admin
https://www.facebook.com/shabbir.jaan.98