Sulphuric acid preparation and properties, Group 16 P Block Elements
Sulphuric Acid (H2SO4) :
It is considered as the king of chemicals. In ancient days, it was called “oil of vitriol” as it has been prepared by the distillation of ferrous sulphate (Green Vitriol)
Manufacture of sulphuric acid (Contact Proces) :
→ Production of sulphur-di-oxide : So, ein be prepared by oxidation of powdered uphur or by roasting of pyrites,
→ Oxidation of Sulphur-di-oxide : SO2 is oxidised into SO3 in presence of atmospheric oxygen. The reaction is carried out in presence of V2O5 catalyst at 2 bar pressure and 720 K temperature.
→ By increasing the production of SO3 we can increase the yield of sulphuric acid. By applying Le-Chateliers principle, we can get the better yield of sulphur trioxide by following conditions are maintained during manufacture.
→ Temperature. The reaction is exothermic bence at low temperature the reaction will go in forward direction, hence at 673-723 K temperature, the yield will be maximum
Pressure : High pressure will favour the process Thus, at 1.5 – 2bar pressure, the yield will be maximum
→ Catalyst: For better yield the presence of catalyst is compulsory because at low temperature, the reaction will be slow. Hence either vunndium pentaoxide (V2O5) or platinised asbestors is used as catalyst.
Excess of Oxygen : For better yield of SO3O2 should be taken in excess.
Puricy of gases: For the prevention of poisoning of catalyst, the must be free from dust, moisture and As2O3.
Conversion of SO3 into H2SO4 production of So, it is absorbed in cone. H2SO4 to get oleum
Oleum may be diluted with calculated amount of water to get H2SO4
The sulphuric acid formed from this method is 96-98% pure.
Plant and its Working :
→ The plant employed for Contact process has been shown below in fig 7.38
This plant consists of the following parts :
→ Pyrite burners : In this part sulphur or ironpyrite is oxidised in presence of excess of air and sulphur dioxide is formed.
S + O2 → SO2
4FeS2 + 11O2 → 2Fe2O3 + 8SO2
→ Purifying Unit : The gases coming out from burners have the impurities of dust particles and arsenic oxides. Before passing the mixture from catalytie chamber it is quite necesary to remove these impurities. These impurities can be removed by passing the uses from following
- Dust Chamber : In dust chamber, steam is passed from the top of the chamber. It helps in removing the dust from the gases by settling these particles
- Coolers: In coolers the temperature of the is reduced to about 373 K
- Scrubbers: Scrubber is a tower in whieh quartz is packed. In this tower, water is sprayed from the top so that dust particles and other water oluble impurities are removed.
- Drying tower in this tower concentrated sulphuric acid is sprayed from the top of the tower so that the moisture present in case can be removed and the mixture may completely dehydrated.
- Arsenie purifier : In this chamber freshly precipitated ferrie hydroxide is present which absorbs the impaurities of arsenic acide. Arsenie Oxide behave a poison for the catalyst.
→ Testing box: The gases coming out from the purification unit, are now pad through the testing box. Here the purity of gases is checked. For the testing of se, a strong beam of light is pred through the box. If the gases are impure then the path of beam will be invisible ie, the light will show Tyndall effect while if the gases are pure then the path of the beam will be invisible. In case if the gases are impure then the gases are furhter passed through purifying unit.
→ Contact tower: Now the pure ses are pre-heated up to about 723-823 K. Then gases passed into converter or contact tower. Contact tower is a cylindrical chamber which is made up of iron. In this chamber iron tubes are also present in which platinised asbestos is packed. But in many other cases V2O5 used because it is more efficient. In this converter, sulphur dioxide is oxidised to sulphur trioxide.
This evolved beat is used in maintaining the temperature needed for the reaction. Thus, preheating is not needed any more.
→ Absorption tower : Sulphur trioxide coming from converter is now passed through this tower. The tower is packed with acid proof flint pieces. Pure concentrated sulphuric acid is sprayed from the top for the abeorption of sulphur triocide. After absorption of SO3 in conc H2SO4, oleum or fuming sulphuric acid is formed
→ By diluting the oleum with calculated amount of water, concentrated sulphuric acid of desired concentration is obtained.
→ SO3 is not abeorbed directly in water because it results forms a dense fog of sulphuric acid which cause much difficulty to the workers. Hence, wulphur trioxide is absorbed over sulphuric acid in order to make the procesa naler to handle.
Physical Properties of Sulphuric acid
- It is a colourless, corrosive and syrupy liquid called oil of vitriol
- Its specific density is 1,84 pm at 20°C
- Its freezing point is 10.5°C and boiling point is 317°C. The high boiling point of sulphuric acid is due to the presence of intermolecular hydrogen bonding which is shown below
- It also has very high viscosity due the presence of intermolecular hydrogen bonding
- It has great affinity for water. It dissolves in water with exothermic process. When water is added to acid spurting takes place
- because a lot of heat is produced during this process. Hence for diluting the acid, always add acid to water slowly and not water to acid.
- It is highly corrosive and produces burns on the skin
Chemical properties of Sulphuric acid
The important chemical properties of sulphuric acid are discussed below
→ Dissociation : Sulphuric acid dissociates partially on heating upto 270°C temperature
→ Acidic character: It is a strong dibasic acid. In aqueous solution, it ionises in two steps
→ Higher value of Ka1 than Ka2 indicates that H2 SO4 is stronger acid than HSO4– In other words, we can say that HSO4– ion has lesser tendency to donate proton or H3O+ ion as compared to sulphuric acid. Since on disociation sulphuric acid forma two types of lona hence it reacts with base and forms two types of salt. These salts are knwon as acidic salts and normal salt.
→ As dehydrating agent: Concentrated sulphuric acid has strong affinity for water and it is highly hygroscopic in nature so it absorbs water ensily. Due to this reason it is used as a dehydrating agent. It ab orbe water from organic compounds like organic acids, sugars, starch, paper, wood, etc. Some examples are given below
Drying of some gases: The gases like O2, N2 HCl, Cl2 etc Which do not react with cone. H2SO4 can be dried by conc. sulphuric acid.
→ Precipitation Reactions : Ba2+, Pb2+ Ca2+ Sr2+ etc. one can be precipitated in the form of sulpbate from their salt solutions.
→ Oxidising properties : Hot and concentrated sulphuric acid behave a strong oxidising agent. The oxidising character of H2SO4 is due to the fact that it decomposes to give nascent oxygen.
Some oxidising reactions are discussed below
→ Oxidation of copper metal In presence of sulphuric acid copper metal is oxidised into copper sulphate.
→ Oxidation of silver metal: It oxidises silver metal into silver sulphate
→ Oxidation of carbon. It oxidises carbon into carbon dioxide
C + 2H2SO4 → 2SO2 + 2H2O + CO2
→ Oxidation of sulphur : It oxidises sulphur into sulphur dioxide
S + 2H2SO4 → 3SO2 + 2H2O
→ Oxidation of HBr and HI: It oxidises HBr into Br2 and HI into I2
2HBr + H2SO4 → Br2 + SO2 2H2O
2HI + H2SO4 → I2 + SO2 + 2H2O
→ Oxidation of phosphorus : It oxidises phosphorus into phonhar acid
→ Oxidation of mercury : It oxidines mercury into HgSO4.
→ Oxidation of naphthalene. In presence of mercury catalyst napthalene in oxidined into phthalic acid by sulphuric acid.
→ Reaction with salts: (a) Dilute sulphuric acid can decomes bicarbonaten carbonates, sulphides, sulphites, nitritos eto at room temperature.
→ Hot concentrated sulphuric acid can decompose the Balts like chlorides, fluorides, nitrates, acetates, oxalates etc.
→ Action with sulphur trioxide : Concentrated sulphuric acid absorbes wulphur trioxide and oleum or fuming sulphuric acid is formed
→ Sulphonation Concentrated sulphuric acid and oleum reacts with aromotie compounds to form sulphonic acids.
→ Action of Potassium ferrocyanide : Carbon mono oxide is formed
→ Reaction with PCl5
→ Reaction with potassium chlorate
Structure of Sulphuric acid
Sulphuric acid as well as sulphate ion both have tetrahedral structure where sulphur atom is op hybridised
Uses of Sulphuric acid
→ It is a very important industrial chemical and mainly used in manufacturing industrial products A nation’s industrial strength can be judged by the quantity od sulphuric acid. It is also known as king of chemicals. Ita main users follow
- In production of fertilizers like ammonium sulphate, super phosphate etc.
- In petroleum refining.
- In leather industry for tanning.
- In textile, paper and dying industries.
- In manufacture of coal tar, dyea and a number of drugs and disinfectants.
- In manufacturing of other acide such as orthophosphoric acid, nitric acid, hydrochloric acid etc.
- In manufacturing of nitro cellulose.
- In storage batteries.
- in manufacturing of paints and pigments.
- In cleansing metals before electroplating, enameling, galvanising and pickling.