Q. Show the Structure of sulphuric acid?

Theoretical considerations require that the reaction be carried out at low temperature and high pressure. However, at low temperature, the reaction is too slow and high pressure makes the cost of plant uneconomical. The yields of S0, are optimised, by using a suitable catalyst, an excess of 0₂, and removing SO₃, formed, the latter two shift the equilibrium to the right.  Optimally the reaction is carried out at 700 - 725 R and one atmosphere pressure using vanadium pentoxide as catalyst and an excess of oxygen.

The purified SO₂, is mixed with air (15) and is passed through a four stage catalytic converter operating between a range of temperatures, Fig. After  conversion of SQ₂ to SO₃, to the  extent of 99.5% or so, the gases come out of the converter.

Reaction of SO₃ with HO₂ is violent and gives a fog of dilute sulphuric acid. Therefore, SO₃ is passed through concentrated H₂S0₄ to give oleum. From oleum, H₂S0₄ of any required concentration can be prepared by appropriately diluting it.

SO₃ + H₂SO₄------------> H₂S₂O₇ (oleum)

H₂S₂O₇ + H₂O----------> 2H₂SO₄

Concentrated sulphuric acid is a colourless, thick, oily liquid having sp.gr. 1.838 at 288 K,

m. p. 283.4 K and b .p. 613 K. At its boiling point, it gives dense white fumes of SO₃.  H₂SO₄, is a strong acid which is' almost completely ionised in aqueous solution. It behaves as adi basic acid, forming two distinct series of salts, namely, hydrogen sulphates, containing HSO: and sulphates, containing SO^2-₄. The dilute acid attacks many metals forming sulphates and hydrogen, but it does not react with lead, copper, mercury and silver.

Zn + H₂SO₄-----------------> ZnSO₄ + H₂

Concentrated H₂, SO₄, dissolves many metals giving sulphur dioxide. But there is no action on gold, platinum. Glass, silica and silicon-steel, the latter is used for making, distillation vessels.

Cu +2H₂SO₄---------------> CiSo₄ + 2H₂O + So₂

Hot concentrated.H₂S0₄ is a good oxidising agent. It oxidises H₂, C, P, S, H₁; HBr to H₂0, CO, H₂PO₃, SO_2, I₂ and Br₂, respectively. It is also a good sulphonating agent.

C + H₂SO₄-----------------> CO + SO₂+ H₂O

C₆H₆ + H₂SO₄------------> C₆H₆ SO₃H + H₂ Benzene suphonic acid

Concentrated H₂SO₄ has a great affinity for water and is used a dehydrating agent. This property of concentrated sulphuric acid is used in drying gases like O₂N₂SO₂ etc. H₂SO₄ chars organic substances by removing elements of water leaving black carbon behind e g.

Below its melting point, anhydrous sulphuric acid is a white crystalline solid consisting of a throw-dimensional hydrogen-bonded network, which persists in the liquid state and makes the liquid viscous. The two hydroxyl groups and two oxygen's are tetrahedrally arranged around  the S atom in H₂S0₄, as shown in Fig. with S-OH and S-O bond lengths being  154 pm and 147 pm, respectively. This shortening of S-O bond shows p? d? bonding between sulphur and oxygen. The bond, as a result, has appreciable double bond character. In SO^2-₄ ion all the four S-0 bond lengths are 149 pm. This indicates extensive - delocalisation of bonding electrons.