Question on Colloids

Fog is a colloidal solution in which a liquid is dispersed in a gas. Is this statement correct?

Umpolung

Umpolung is a phenomenon in which the polarity of an atom (usually the carbon) is reversed. This opens up reactions on a functional group which is otherwise not possible. Umpolung is a German word meaning reversed polarity.

Two common reactions that showcase umpolung are benzoin condensation and reactions involving carbonyls and dithianes.

Benzoin Condensation

Benzoin Condensation is a reaction between two aromatic aldehydes catalysed by alcoholic KCN. The reaction begins with the nucleophilic attack of the cyanide ion on the carbonyl group which is followed by a rearrangement of the intermediate formed leading to reversal of polarity at the carbonyl carbon. The carbonyl carbon which is otherwise positive becomes negative after the rearrangement.

The carbon atom which is now negatively charged acts as a nucleophile and atatcks another molecule of the aromatic aldehyde leading to the formation of the product after a couple of steps including the one that eliminates the cyanide ion.

Dithiane Reactions

Ethylene diol is generally used to protect carbonyl compounds from undergoing any unwanted reaction in certain reactions. If the sulphur anolog (ethane-1,2-dithiol) of ethylene diol is used in protecting the carbonyl group, it opens up an opportunity of reversing the polarity of the carbonyl carbon which is otherwise not possible with ethylene diol.

The carbonyl carbon can carrying a negative charge is favoured as the negative charge can gain stbility by resonating in the vacant orbitals of sulphur atom which is not possible with oxygen atom in its place.

Question on Solid State

If “x ” is the edge length of the unit cell of a face centred cube formed by an atom of radius “r ”, what is the relationship between x and r ?

Limonene

Limonene is an optically active hydrocarbon whose D-isomer possesses a strong smell of oranges. The name suggests it to be an alkene and since it is found in large concentration on the peel of lemons, it is named limonene. It is a cyclic terpene and is used in the synthesis of carvone which is used in the food industry and also in the flavour industry.

The fact that limonene cracks to form isoprene at very high temperatures suggsest that it is a product of the Diels Alder reaction between two isoprene units.

Limonene is also used in food industry and also in some medicines.

Question on Qualitative Analysis

A reddish brown gas, obtained on heating an inorganic compound with K₂Cr₂O₇ and conc. H₂SO₄ was bubbled through dil. NaOH. The alkaline solution yielded a yellow precipitate on addition of lead acetate. What anion is present in the inorganic compound?

Question on Osmotic Pressure

What amount of Urea should be present in a 100mL solution to produce an osmotic pressure of 20.4atm?

Question on pKa values

How will the pKa values 9, 13 and 20 be assigned to the hydrogen atoms marked as a, b and c respectively?

Question on Basic Strength

What is the correct ascending order of basic strength for the following molecules?

Question on gem-diols

Which of the following gem-diols is most stable?

Question on Stoichiometry

How many grams of carbon dioxide will be produced on complete combustion of two moles of ethyl alcohol?