Group-A
Physical Chemistry
Boyle's Temperature (TB):
The temperature at which normal gases start to behave like ideal gases (due to the absence of both attractive and repulsive forces at that particular temperature).
TB = a/Rb
Causes of Deviation of Real Gasses from Ideal Behaviour:
The causes of deviations from ideal behaviour may be due to the following two assumptions of kinetic theory of gases-
1. The volume occupied by gas molecules is negligibly small as compared to the volume occupied by the gas. (is valid only at low pressures and high temperature,)
2. The forces of attraction between gas molecules are negligible. (is not valid when the pressure is high and temperature is low)
Colligative Properties:
Colligative properties are the properties of dilute solution and is depend upon the number of solute particles not on the nature of solute particles in the solution.
When a solute particle undergoes association or dissociation in the solution, the number of solute particles change. Consequently, abnormal value of colligative properties obtained.
It is of four types. They are-
1. Lowering of vapour pressure
2. Elevation in boiling point
3. Depression in freezing point
4. Osmotic pressure
Vapour Pressure:
The pressure exerted by vapour on the surface of liquid is called vapour pressure of that liquid at constant temperature.
Vapour pressure of the solution is lower than that of pure solvent.(think why?)
We know that in solution, two component are present. One is solvent and other is solute. Generally solute is nonvolatile. So its Vapour pressure is almost zero. So, its contribution to total vapour pressure of solution is nothing. Consequently, the vapour pressure of solution is actually vapour pressure of solvent of the solution. Hence, the vapour pressure of the pure solvent is more that that of solution.
Lowering of Vapour Pressure:
The vapour pressure difference between pure solvent and solution is called lowering of vapour pressure.
If vapour pressure of pure solvent is Po and that of solution is P, then lowering of vapour pressure is
Po − P
Relative Lowering of Vapour Pressure:
The ratio of lowering of vapour pressure to vapour pressure of the pure solvent is called relative lowering of vapour pressure.
If vapour pressure of pure solvent is Po and that of solution is P, then relative lowering of vapour pressure is
(Po − P) / Po
Relative lowering of vapour pressure is equal to mole fraction of the solute(Raoult's Law).
(Po − P) / Po = Xsolute
Osmosis:
The spontaneously flow of solvent particles from low to high concentrated solution through a semipermiable membrane is called osmosis.
Whe a dried pea is placed in water it gets swelled after sometimes due to inward movement of water through its outer cell wall which acts as a semipermeable membrane.
Osmotic Pressure:
The smallest amount of pressure required to stop the osmosis is called osmotic pressure.
We know that solvent flows from low concentrated solution to high concentrated solution through a semipermeable membrane(i.e. osmosis). So these flow will stop by applying pressure on the high concentrated solution side, This pressure is called osmotic pressure of the solution. It is denoted by π
Measurement of Osmotic Pressure:
Class Work
Isotonic Solution:
When two solutions have the same osmotic pressure as well as same molar concentration.
i.e. π1 = π2
or, C1 = C2
Therefore, when two solutions are separated by a semipermeable membrane , the solvent flow from solution of lower osmotic pressure to solution of high osmotic pressure until both the solutions will become isotonic.
Van't Hoff's Factor:
Elevation in Boiling Point:
Depression in Freezing Point
Specific or Electrolytic Conductance (κ):
The resiprocal of specific resistance (ρ) is called specific conductance.
We know that-
R ∝ l/a
where, l is length of the wire and a is cross sectional area of the wire
or, R = ρ. l/a
or, 1/ρ = 1/R . l/a
or, κ = π . l/a
Unit of κ = ohm−1 . cm/cm2
ohm−1 . cm−1
Its S.I. unit is Sm−1
when, l = 1 and a = 1
then, κ = π
So, specific conductance is the conductance od a conductor of unit length and unit cross sectional area. For electrolytic solutions, the conductance of one cc of the solution is called its specific conductance.
Equivalent Conductance (Λ):
It is denoted by capital lambda(Λ) and is conductance of V cc of the solution containing one gm-equivalent of an electrolyte. So, it is the product of Specific or Electrolytic Conductance (κ) and the volume of the solution (V) in cc containing one-gm equivalent of the electrolyte.
or, Λ = κ . V
If the concentration of a solution is C g-equivalent/liter, then-
C g-equivalent is present in 1000cc of the solution.
so, 1 g-equivalent is present in 1000cc/C of the solution.
or, Volume in cc containing one gm-equivalent = 1000/C
so, Λ = 1000.κ/C
Unit of Λ = κ/C = ohm−1 . cm−1/eq-cm−3
or, ohm−1 . cm2 / eq−1
Cell Constant:
We know that the resistance (R) is given by-
R ∝ l/a
or, R = ρ. l/a
or, 1/ρ = 1/R . l/a
or, κ = π . l/a
where, ρ is specific conductance, l is length of wire, a is cross sectional area of the wire κ is specific conductance and π is conductance of conductor.
The ratio of l to a is called cell constant.
Hence, cell constant = κ / π = κ . R
Unit of cell constant:
l/a = cm/cm2 = cm−1
Effect of dilution on conductivity:
The specific conductance depends on the number of ions present per cc of the solution. Though degree of dissociation increases on dilution but the number of ions per cc decreases. So, the specific conductance decreases on dilution.
The equibvalent conductance is the product of specific conductance and volume of the solution containing one gm-equivalent of the electrolyte.
Λ = κ . V
As the decreasing κ value is more than compensated by the increasing V value, hence, Λ increases. on dilution.
Kohlrausch's Law:
The equivalent conductivity of an electrolyte at infinite dilution (Λo) is the sum of the ionic conductivities of their cations and anions.
Λo = λ+ + λ−
where- λ+ and λ− are cationic and anionic conductivities at infinite dilution respectively.
Applications:
Useful in
calculating equivalent conductivity at infinite dilution.
Calculation of degree of dissociation of an electrolyte.
Calculation of solubility of sparingly soluble salt,
Calculation of ionic product of water.
The part of universe which is under study is called system and the rest part of the universe is called surrounding. That means the universe is the combination of system and surrounding.
The system which can exchange both heat and matter with the surrounding is called open system. Hot water in a beaker is an example of this system.
The system which can exchange only heat but not matter with the surrounding is called closed system. Hot water in a sealed tube is an example of this system.
The system which can exchange neither energy nor matter with the surrounding is called Isolated system. Hot water in a thermos flask is an example of this system.
When a system changes itself from one to another state, the operation is called procss.
The process which takes place at constant temperature is called isothermal process.
i.e. ΔT=O
The process in which no heat change occurs is called adiabatic process.
i.e. ΔQ=O
The process which takes place at constant volume is called isochoric process.
i.e. ΔV=O
The process which takes place at constant pressure is called isobaric process.
i.e. ΔP=O
The process which takes place infinitesimally slowly and whose direction at any point can be reversed by applying an infinitesimal change in the state of the system is called reversible Process.
The process which takes place in one step and can not be reversed. This is a fast process.
Properties which depend upon the amount of the substance present in the system are called extensive properties. Mas, Volume, Number of moles, Enthalpy, Entropy, Free energy etc are the example of extensive properties. These properties are additive. If mass of the gas is changed, the volume is also changed and so is the number of moles and their internal energy of the system.
Properties which don't depend upon the amount of the substance present in the system are called intensive properties. Temperature, Pressure, Boiling Point, Melting Point etc are the example of intensive properties. If temperature of a glass of water is 25oC, then each and every drop of water in this glass has the temperatue of 25oC. These properties are non additive.
All forms of energy associated with a system is called internal energy or simply energy of the system (E).
This is expressed in Joule. This arises due to movement of molecules, arrangement of atoms in molecules, number of arrangement of electrons in atoms etc.
It is neither possible nor necessary to calculate the absolute value of internal energy of a system. It is a state function so depend only on the initial and final state of the system.
The amount of heat required to change its temperature by one degree of a substance.
Q = CΔT
or, C = Q/ΔT
The amount of heat required to change its temperature by one degree of one mole of a substance.
The amount of heat required to change its temperature by one degree of a substance at constant pressure.
The amount of heat required to change its temperature by one degree of a substance at constant volume.
We know that
H = E + PV
or, H = E + RT (as PV = RT for one mole)
differentiating the above equation w.r.t T, we get-
dH/dT = dE/dT + R(dT/dT)
or, CP = CV + R
or, CP − CV = R
It is also called energy conservation principle. According to this principle, energy can neither be created nor be destroyed, it can only be transfer or change fron one form to another form.
In other way-
Heat absorbed (Q) by the system is equal to change in internal energy (ΔE) plus work done by the system (−W).
Q = ΔE + (−W)
or, ΔE = Q + W
Limitations:
First law does not indicate whether heat can flow from a cold body to a hot body or not.
First law does not specify that process is feasible or not.
Practically it is not possible to convert the heat energy into an equivalent amount of work.
Let us consider 'n' moles of an ideal gas enclosed in a cylinder fitted with a frictionless, weightless and movable piston. Let P be the pressure of the gas and P-dP be the external pressure under which volume of the gas increased by dV, then work done in this expansion is
dw = −(P − dP)dV = − PdV (as dP.dV is very small).
For a infinite volume change from V1 to V2, the total work done during expansion-
where P1 and P2 are the initial and final pressure respectively.
Question: 3 moles mole of and ideal gas are expanded isothermally and reversibly from volume of 10 m3 to the volume 20 m3 at 300 K. Claculate the work done by the system. (Answer: 5.178 KJ)
When a gas is allowed to expand from high to low pressure through a porous plug under adiabatic conditions, the gas gets cooled. The drop in temperature (dT) produced by fall in pressure (dP) under adiabatic condition is called J-T Effect. The fall in temperature is due to decrease in kinetic energy of the gas molecules. Since a portion of it is used up in overcoming the vander waal force of attraction existing among them during expansion. Since ideal gas has no such forces, therefore, there is no expenditure of energy in overcoming these forces during expansion.
The temperature at which Joule - Thomson Coefficient becomes zero is called Inversion Temperature(Ti).
Ti = 2a/Rb
Group-B
Inorganic Chemistry
Group-C
Organic Chemistry
Geometry of Organic Compounds:
Class Work
Detection of Nitrogen:
Sodalime Test:
The given substance is mixed with double the amount of sodalime and heated in a test tube. The vapour of ammonia evolved show the presence of nitrogen.
Sodium Test (Lassaigne's Test):
This is a golden test for the detection of nitrogen in all classes of nitrogenous compounds. It involves the following steps:
The substance is heated strongly with Na metal
Na + C + N → NaCN
The water extract of the fused mass is boiled with ferrous sulphate solution.
FeSO4 + 2NaOH → Fe(OH)2 + Na2SO4
6NaCN + Fe(OH)2 → Na4[Fe(CN)6] + 2NaOH
To the cooled solution is then added a little ferric chloride solution and excess of concentrated HCl.
Na4[Fe(CN)6] + 4FeCl3 → Fe4[Fe(CN)6]3 + 12NaCl
prussian blue
The formation of prussian blue or green coloration confirms the presence of nitrogen in given organic compound.
Detection of Halogens:
Sodium Test:
Upon fussion with sodium, the halogens in the organic compound are converted to the corresponding sodium halides. Thus,
Cl + Na → NaCl
Br + Na → NaBr
I + Na → NaI
Acidify a portion of sodium extract with dilute HNO3 and add to it AgNO3 solution.
White ppt. soluble in ammonia indicates Chlorine
Yellowish ppt. sparingly soluble in ammonia indicates Bromine
Yellow ppt. insoluble in ammonia indicates Iodine.
Detection of Sulphur
Sodalime Test:
If sulphur is present in the given organic compound, upon fussion with Na reacts to form sodium sulphide.
2Na + S → Na2S
Thus, the sodium extract obtained from the fused mass may be tested as:
A. To a portion, add freshly prepared sodium nitropruside solution. A deep violet coloration indicates the presence of sulphur.
B. Acidify a second portion of the extract with acetic acid and then add lead acetate solution. A black ppt. of lead sulphide confirm the presence of sulphur.
Pb(CH3COO)2 + N2S → PbS + 2CH3COONa
Lead Acetate Black ppt.
Grignard Reagent/Alkyl magnesium halide (R-Mg-X)
Method of Preparation:
Grignard Reagent may be prepared by the reaction of alkyl halide with Mg metal in presennce of dry ether.
R-X + Mg → R-Mg-X
Some Important Reactions:
Details in Class Room
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