Oxidation State of Carbon

An element forms a molecule by sharing or donating/accepting electrons.

If it is sharing, it is covalent bond, if it is by donating/accepting electrons, it is an ionic bond.
The degree of oxidation of an element in a molecule is called oxidation state.This is particularly significant where an element can exhibit variable valency.
Oxidation states of free atoms are zero.

The oxidation state of free ion is the charge carried by it.

The sum of all oxidation states in a neutral molecule is zero.

The oxidation states of hydrogen is +1 and oxygen -2 with a few exceptions.

Introduction :

Carbon has configuration 2s² 2p²
as shown under

The valency and therefore the oxidation state is expected to be 4 or -4 as it would donate or accept 4 electrons to attain stability.

The oxidation state is therefore variable in carbon from -4 to +4
Concider a compound like CO₂

oxygen has -2 oxidation state,
the sum of oxidation state of carbon and oxygen is zero since the molecule is neutral.
-2 x 2 + carbon oxidation state=0

oxidation state of carbon = +4
Similarly for a compound like CH4,
the oxidation state would be

+1 x 4 + oxidation state of carbon = 0
oxidation state of carbon = -4

Now consider another reaction where in oxidation number of carbon undergoes change and has variable oxidation state CH₂=CH₂ + H₂O  CH₃-CH₂OH

oxidation states of carbon in ethene: -2 , -2 ; and in ethanol they are : -3 -1

Other Compounds.

Let us consider a molecule of CO.

The oxygen has -2 oxidation state.

The oxidation state of carbon is therefore found out as under
-2 + oxidation state of carbon = 0
oxidation state = -2

Let us consider a molecule of CF4.

The fluorine has -1 oxidation state.

The oxidation state of carbon is therefore found out as under
-1x 4 + oxidation state of carbon = 0
oxidation state=+4

Let us consider a molecule of CH3Cl.

The chlorine has -1 oxidation state. The hydrogen has +1 oxidation state.

The oxidation state of carbon is therefore found out as under
-1  + 1 x 3 + oxidation state of carbon = 0
oxidation state= +2

Liquid oxygen temperature

Introduction :

Oxygen gas is in the air around us which also includes many other gases. Air is cooled to a certain temperature will change into a liquid or a solid.Among the elements in the universe, oxygen is the third most abundant and makes up to 21% of the earth's atmosphere.Carl Wilhelm and Joseph Priestley independently discovered oxygen, by heating mercuric oxide (HgO).

How we Obtain Liquid Oxygen?

Oxygen turns into a liquid at -183 degrees Celsius. To bring these gases to such low temperatures, the air is cooled and compressed. When allowed to expand again, their temperature drops further. To extract the oxygen, the liquid is so warmed that just nitrogen turns back into gas - leaving behind liquid oxygen.

Liquid form of oxygen depends on two things:

• Pressure
• Temperature

Storing of liquid oxygen:
Oxygen is kept in cryogenic, insulated containers called dewars which keep the oxygen in liquid form at -170 degrees Celsius. Temperature outside the storage tank is much higher than the liquid temperature. Due to the heat leak, the liquid tends to warm up thus producing gaseous oxygen that contributes to a rise in pressure inside the tank.

Image on liquid oxygen  

Temperatures of Liquid Oxygen

Oxygen turns into a pale blue color liquid at temperatures below its boiling point of -183�C and weighs 1.14 times the weight of water. At temperatures more than -118.6�C, the liquid oxygen will become a gas in spite of the pressure exerted on it. This is the critical temperature for liquid oxygen. 1 Liter of liquid oxygen can turn into 860 Litres of gas.
Boiling Point at 1 atm: -183.0°C, 90.15K, -297.4°F
Oxygen is in liquid phase from -297.4°F @ 1 atm. to -181°F and 731psi.

Conclusion to Temperatures of Liquid Oxygen

We can conclude that, liquid oxygen, in combination with liquid hydrogen, makes an excellent rocket fuel. Liquid oxygen is a versatile and efficient method of supplying oxygen to patients at home.

Triple Point Temperature

Introduction:

Definition Temperature:

The temperature means the degree of hotness and coldness of any particular substance.There are so many different types of the temperature such as the critical temperature, Curie temperature, triple point temperature etc. Critical temperature for the conductors is the temperature at which it loses its resistance completely. Curie temperature is the temperature at which the magnet loses its magnetism completely on heating. Here we discuss about the triple point temperature of any substance. The image below shows the different phases of water.

Examples of Triple Point Temperature

The triple point temperature of the substance is defined as the temperature at which that particular substance exists in all the three phases of matter, i.e., it exists in the form of solid, liquid and gas at that particular triple point temperature in the thermodynamic equilibrium. For example, the triple point temperature of the mercury is – 38.84°C, the triple point temperature of hydrogen is 13.8033 K and the triple point temperature of water is 0°C or 273.16 K.
Generally, the combination of pressure and the temperature at which the substance can exists in the stable equilibrium. In case of water, the triple point temperature is 273.16 K that means water exists in the form of ice, water and vapour at temperature 273.16K. In case of the triple point temperature, the surfaces separating the different phases should be perfectly flat so that there is no effect of the surface tension.

Conclusion for Triple Point Temperature

From the above discussion and the concept of the triple point temperature, the phase diagram of water is too complex. At the high temperature the pressure increases results first in liquid and then solid water. At the lower temperature, the liquid state disappears very slowly and then water converted into gas to solid. When the temperature is above that of the triple point at the constant pressure, the ice convert solid into liquid (water) and then steam (water vapour).
At the temperature below the triple point at the constant pressure almost zero that means in the outer space the liquid form of the water does not exists. In the process of the sublimation, the ice directly converts in the form of steam when it is heated.

Specific Heat Cv

Introduction:

Molar specific heat capacity of a gas at constant volume Cv is defined as the quantity of heat required to raise the temperature of one mole of a gas through 1 K keeping its volume constant.
Specific heat Cv of ,monoatomic , diatomic are discussed here.

Specific Heat Cv of Monoatomic Gases:

Monoatomic gases like argon helium have three degrees of freedom.
We know , kinetic energy per molecule , per degree of freedom is `1/2` kT
Therefore kinetic energy  per molecule with three degrees of freedom is `3/2` kT
Total kinetic energy of one mole of the monoatomic gas is given by
 E =`3/2` kT* N
    = `3/2` RT, where N is Avogadro number
 `(dE)/(dT) = 3/2R`
If dE is small amount of heat required to raise the temperature of 1 mole of the gas at constant volume, through a temperature dT
dE = 1 x Cv x dT
Cv = = `(dE)/(dT) = 3/2 R`
As R = 8.32 J mol^-1K^-1
Cv = `3/2` 8.31
Cv = 12.465 J mol^-1 K^-1
Cp is molar specific heat at constant pressure.
Then Cp –Cv = R
Cp = CV +R
     = `3/2`  R +R = `5/2` R = `5/2`  x 8.32 = 20.775 J mol^-1K^-1

Specific Heat Cv of Diatomic Gases:

In diatomic gases like hydrogen , oxygen , nitrogen etc, a molecule has five degrees of freedom. Hence the total energy associated with one mole of diatomic gas is
     E = 5 x `1/2` kT x N = `5/2` RT
Also Cv = `(dE)/(dT)`  = `d/(dT) (5/2 RT)`
              = `5/2` R
Cv = `5/2` x 8.31 = 20.775 Jmol^-1K^-1 
But Cp = Cv +R
            = `5/2` R +R
            = `7/2` R
            = `7/2` x 8.31 = 29.0.85 J mol^-1K^-1

Heat Transfer Designs

Introduction :

Heat transfer:- There are three modes of heat transfer for different form of substance we have different method of transfer of heat. Like for solids mode of transfer of heat is conduction. Conduction is a process of heat transfer in solids. In this process, heat is transferred from particles to particles of the solid, without the actual movement of the particles.

 

We can see the simple experiment for this

1. Put drops of wax at regular intervals on an iron rod( or any other metal).
2. Heat one end of the rod over a candle flame.
3. Repeat the procedure using a plastic rod.

Observation and Conclusions for Heat Transfer

Observation:

1. With the metal rod:- the drop nearest to the flame melts first, one by one all the drops melts, and the end of the rod opposite to the flame begins to feel warm to the touch.
2. With plastic rod :- the end closer to the flame begins to melt while the wax drops remain unaffected. Also, the rod does not feel warm to the touch.

Conclusion:

1. Certain material for example allows heat to pass through them while certain material does not.
2. The heat is transferred from particles to particles themselves moving. This is inferred from the fact that the entire rod does not get heated at once. The wax drops melt one by one gradually. This mode of heat transfer is called conduction.

Heat Transfer by Convection

Convection:- convection is the transfer of heat through a body by the hot particles themselves moving from place and place.
Transfer of heat by convection takes place in liquid and gases only. It does not occur in solids because the particles in solids are not free to move about.
One example when a beaker of water containing a crystal of potassium permanganate is heated over a low flame, an upward current of colored water is seen rising from the point where heat is applied. This colored stream reaches the top, spreads out and circulates down the sides of the beaker.
These were the some points related to heat transfer. Knowledge of this much is very important.

si Unit of Heat Energy

Introduction :

Heat: Heat is a form of energy. It gives the feeling of hotness and establishes its existence .The Sun is the natural source of heat and light. Heat light is required for the process of Photosynthesis. We need heat energy for our daily activities. Heat energy is necessary to heat water, to cook, to manufacture glass, cement, and iron in factories. The food we take provides heat energy to us.

Sun is the natural source of heat.
Abundant heat and light we get from the sun.Solar energy is necessary for all the activities on the earth.Can you tell how rain is formed?Due to heat.

Heat is a Form of Energy and its Units

How can we say that is form energy?Is there any basis for it ?Energy is the ability to do work.Energy can be converted from one from to another.If heat is a from of energy.,it should be able to to do work.It should also be possible to convert heat into other forms of energy.
Since heat is a form of energy,should not the units of heat be the same of energy?The international unit of heat is called joule.Another unit called calorie is also used as the unit of heat.How much heat is a calorie? The amount of heat required to raise the temperature of one gram of water by one degree Celsius is called calorie.

History of Joule

The international unit of heat(any other form of energy) is called joule in honor of the British scientist James pres cot Joule.joule was accepted as the international unit of heat in 1948.

Meaning of calorie:
It is the amount of heat needed to increase the temperature of 1KG of water by 1⁰c.

Sulfur Dioxide Chemical Formula

Introduction to Sulphur dioxide:

The chemical formula of sulphur dioxide is SO₂. Molar mass of sulphur dioxide is 64.07g. Sulphur dioxide is a colorless gas with irritating and suffocating smell. Its meting and boiling point are -75.5˚ and -10˚C. Sulphur dioxide can be produced by some industrial processes and also by volcanoes.  Coal and some petroleum contain sulphur, so the combustion of coal and petroleum produces sulphur dioxide. The oxidation of sulphur dioxide can be carried out in presence of catalyst like NO₂ which forms H₂SO₄ that leads to acid rain.
The molecular formulas of the sulphur dioxide is as shown below,

Preparation of Sulphur Dioxide:

Sulphur dioxide can be prepared in many differnt methods; few of them are as follows

• It is prepared by burning sulphur in atmosphere.

S₈ + 8 O₂ ===> 8 SO₂

• It is also prepared by burning or roasting iron pyrites in air.

4 FeS₂ + 11 O₂ ===> 2 Fe₂O₃ + 8 SO₂.

• It is prepared in laboratory by heating copper turnings with concentrated H₂SO₄

Cu + 2H₂SO₄ ===> CuSO₄ + SO₂ + 2H₂O.
Reactions of sulphur dioxide:

• Sulphur dioxide reacts with alkali solutions to give sulphites.

SO₂ + 2 NaOH ===> Na₂SO₃ + H₂O

• Sulphur dioxide reacts with halogens and gives sulphuryl chloride.

SO₂ + Cl₂ ===> SO₂Cl₂.

• Hydrogen sulphide reduces sulphur dioxide and gives sulphur element.

SO₂ + 2 H₂S ===> 3 S + 2 H₂O.

Structure and Bonding in Sulphur Dioxide:

Sulphur dioxide is a bent shaped molecule with O-S-O bond angle 119˚ and the bond length of S-O is 143.1 pm. The sulphur atom is sp² hybridized. The oxidation state of sulphur is +4.
The possible resonance structures of Sulphur dioxide SO₂.

Uses of Sulphur dioxide (SO₂):

• Sulphur dioxide is used in the production of sulphuric acid.
• It is used as a preservative for dried fruits and apricots.
• It is used as a reducing agent and refrigerant
• It is also used as a solvent for some reactions.
• It is used in making wine.

Safety Measures:

Inhaling of sulphur dioxide causes some respiratory diseases and symptoms, which leads to difficulty in breathing and premature death. It also changes lung’s defences and causes some cardiovascular diseases. People who are suffering from asthma, lung or heart disease are much sensitive to sulphur dioxide. Sulphur dioxide not only affects human being but also it damages trees and crops along with oxides of nitrogen.  And, also causes the formation of microscopic aerosols of acid which have serious health implications.