Chemistry Test - 1

(1) Hydrogenation of an alkene is a heterogeneous process which occurs on the surface of a solid catalyst (PtO₂ or Pd/C). The addition occurs with syn stereochemistry (both hydrogens add from the same side). For cis isomer, the product is a meso compound.

(3) The addition of two hydroxyl groups involves syn addition (on the same side of a double bond). The result is same as that of hydrogenation. The cis isomer produces meso compound.

(4) The addition of two hydroxyl groups involves syn addition (on the same side of a double bond). The result is same as that of hydrogenation. The trans isomer produces racemic mixture.

Considering the inductive effect and the steric hindrance of alkyl groups, CH₃NH₂, (CH₃)₂NH and (CH₃)₃N can be arranged in the increasing order of their basic strengths as follows.

(CH₃)₂NH > CH₃NH₂ > (CH₃)₃N

In C₆H₅NH₂, N is directly attached to the benzene ring. Thus, the lone pair of electrons on the N−atom is delocalised over the benzene ring. Again, due to −I effect of C₆H₅ group, the electron density on the N−atom in C₆H₅NH₂ is lower than that on the N−atom in (CH₃)₃N. Therefore, (CH₃)₃N is more basic than C₆H₅NH₂. Considering the inductive effect and the steric hindrance of alkyl groups, CH₃NH₂, (CH₃)₂NH, (CH₃)₃N and C₆H₅NH₂ can be arranged in the increasing order of their basic strengths as

(CH₃)₂NH > CH₃NH₂ > (CH₃)₃N > C₆H₅NH₂ 

Note: This is the correct order in case of aqueous solutions.

In the gas phase, the order would be (CH₃)₂NH > (CH₃)₃N > CH₃NH₂ > C₆H₅NH₂

The lone pair of electrons on the -NH₂ group is donated towards the benzene ring due to resonance effect. As a result, acidic character of -COOH group and basic character of -NH₂ group decrease. Therefore, the weakly acidic -COOH group cannot transfer an H⁺ ion to the weakly basic -NH₂ group. Thus, o- and p-aminobenzoic acids do not exist as zwitter ions.

The paramagnetic substances are those which are freely magnetised when placed in a magnetic field. All the species which have unpaired electrons, are paramagnetic. When placed in a magnetic field, the domains of the unpaired electrons get aligned in the same direction. 

KO₂, the superoxide of potassium, is paramagnetic because it has unpaired electrons.

SiO₂, TiO₂ and BaO₂ are all diamagnetic, as they have paired electrons.

Since the nucleus does not contain b-particle, it is produced by the conversion of a neutron to a proton at the moment of emission.

Hydrogen peroxide (H₂O₂) can act as an oxidising as well as a reducing agent. 

H₂O₂ as a reducing agent: 

Ag₂O + H₂O₂  2Ag + H₂O + O₂

H₂O₂ as an oxidising agent:

PbS + 4H₂O₂  PbSO₄ + 4H₂O

The reaction is known as Sandmeyer reaction. The Sandmeyer reaction is a chemical reaction used to synthesise aryl halides from aryl diazonium salts. 

Strecker reaction: The Strecker synthesis is a preparation of α-aminonitriles.

For example:

Wolff-Kishner reaction (Reduction): The Wolff-Kishner reduction is an organic reaction used to convert an aldehyde or ketone to an alkane using hydrazine, base, and thermal conditions.

Stephen reduction reaction: The Stephen reaction is used to prepare aldehydes from nitriles or cyanides. 

C₃H₈ + 5O₂ 3CO₂ + 4H₂O

C₅H₁₂ + 8O₂ 5CO₂ + 6H₂O

Let the volume of C₃H₈ be 'a' and that of C₅H₁₂ be 'b'.

Now, 'a' L of C3H8 gives '3a' L of CO2 on combustion and 'b' L of C₅H₁₂ gives '5b' L of CO₂.

Under similar conditions of temperature and pressure, PV = nRT

Or, V  n

Therefore, a + b = 1 L and 3a + 5b = 3.5 L 

On solving, we get 

a = 0.75 L and b = 0.25 L