Chemistry Test - 7

The metal atom loses electron and combines with ammonia molecule.

$\text{M}+\left(\text{x}+\text{y}\right){\text{NH}}_3\to {\left[\text{M}{\left({\text{NH}}_3\right)}_{\text{x}}\right]}^{+}+{\text{e}}^{-}\left({\text{NH}}_3\right)\text{y}$ solvated electron.

These ammoniated electrons are responsible for blue colour and conductivity of the solution which behaves paramagnetic.
Main Concept :
Solubility of alkali metals in liquid ammonia

Unlike most metals, the alkali metals dissolve slowly in liquid ammonia, forming hydrogen gas and the alkali metal amide (MNH₂, where M represents an alkali metal): This was first noted by Humphry Davy in 1809 and rediscovered by W. Weyl in 1864. The process may be speeded up by a catalyst. The amide salt is quite insoluble and readily precipitates out of solution, leaving intensely coloured ammonia solutions of the alkali metals. In 1907, Charles Krause identified the colour as being due to the presence of solvated electrons, which contribute to the high electrical conductivity of these solutions. At low concentrations (below 3 M), the solution is dark blue and has ten times the conductivity of aqueous sodium chloride; at higher concentrations (above 3 M), the solution is copper-coloured and has approximately the conductivity of liquid metals like mercury.In addition to the alkali metal amide salt and solvated electrons, such ammonia solutions also contain the alkali metal cation (M⁺), the neutral alkali metal atom (M), diatomic alkali metal molecules (M₂) and alkali metal anions (M⁻). These are unstable and eventually become the more thermodynamically stable alkali metal amide and hydrogen gas. Solvated electrons are powerful reducing agents and are often used in chemical synthesis.

Jones reagent oxidises alcohols to aldehydes and alcohols to ketones without affecting doubled bond.

Main Concept :
Preparation of aldehydes and ketones by Selective oxidation of alcoholsOxidation of Alcohols to Aldehydes or Ketones:

Reagents:
(i) PCC
(ii) PDC
(iii) Cu/$∆\mathrm{ }$
(iv) Jone's reagent
(v) Chromic anhydride in acetic acid

The outcome of the oxidation of an alcohol depends on the type of oxidizing agent used and on the substituents at the carbon atom bearing the OH group.

I. Primary alcohols are first converted to aldehydes which are frequently oxidized further to carboxylic acids in a fast reaction.

II. Secondary alcohols yield the corresponding ketones.

III. Tertiary alcohols cannot be oxidized unless harsh conditions are used that cause complete structural degradation.

All reactions are reversible under reductive conditions.

Selective oxidation of primary alcohols to aldehydes is the most difficult preparation to be carried out. In most cases, further oxidation to carboxylic acid is being observed even under mild conditions and the use of only one equivalent of oxidizing agent. Since the oxidation of primary alcohols to aldehydes is a synthetically important reaction, many attemps have been made to develop reagents for just this purpose. Unfortunately, no generally applicable method is available; Dess-Martin, PCC, PDC, etc.). Usually, several methods have to be tried to find the best reaction conditions for the conversion.

+I group have rich electron clouds which can be donated. So this stabilises a carbocation and destabilises a carbanion
Main Concept :
Concept of Inductive effect

In chemistry and physics, the inductive effect is an experimentally observable effect of the transmission of charge through a chain of atoms in a molecule, resulting in a permanent dipole in a bond.

Solved example :

1)   The inductive effect can be best described as :
a) The conjugation of σ - bonding orbital with the adjacent n - orbital.
b) The ability of atom or group to cause bond polarization
c)   The transfer of lone pair of electrons from more electronegative atom to lesser electronegative atom in a molecule.
d)   All of the above.

2)   Which of the following statement is incorrect about the inductive effect?
a)   It is a permanent effect
b)   It decreases with increases of distance
c)   It involves delocalization of n - electrons
d)   It involves displacement of σ - electrons

For adiabatic expansion of ideal gas the relationship between b & b is b constant

Main Concept :
Thermodynamic Processes (Isobaric, Isochoric, Isothermal and Adiabatic)Types of Thermodynamics Process

A thermodynamic process is said to occur when the state of a system changes from one state (initial state) to another (final state).

1. Isothermal process: It is the process carried out at a constant temperature, dT = 0. For this process, the system is usually kept in contact with a constant temperature bath (thermostat) and the constant temperature is maintained by the exchange of heat with the thermostat.

2. Adiabatic process: It is the process in which heat cannot leave or enter the system, dq = 0. For this process, the system is thermally insulated from the surroundings.

3. Isobaric process: It is the process carried out at a constant pressure, dp = 0. All reactions carried out a atmospheric pressure are examples of isobaric process. However, volume change always takes place in an isobaric process.

4. Isochoric process: It is the process in which the volume of the system is kept constant (dV = 0). For example, heating of a substance in a non-expanding chamber.

5. Cyclic process: It is the process in which the initial and final states are indentical.

6. Reversible process: It is the process in which the energy change in each step of the process can be reversed in direction by making a small change in any property of the system, such as temperature, pressure, etc. Two imortant criteria for a process to be reversible are:

(a) The change must be performed at an infinitesimal slow rate.

(b) Threre must be no loss of energy due to friction and no finite temperature differences.

7. Irreversible process: It is the process in which the system or surroundings are not restored to their initial state at the end of the process. All process ocurring spontaneously in nature are irreversible. They always tend to proceed in a definite direction; and do not proceed in the opposite direction without the actions of an external force. Irreversible processes take place spontaneously and not in infinitesimal slow steps that can be reversed. Some examples of irreversible process are expansion and diffusion of gases, flow of heat from a hotter body to a colder body, etc.
Other Concepts :

Concept 1 :
Adiabatic reversible expansionReversible Adiabatic Expansion (or compression) of an Ideal Gas

[More generally the heat capacity for a molecular species has a temperature dependence that can be approximated as