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Experiments with sulfuric acid

Updated on December 9, 2015

Sulfuric acid 3D ball diagram

Sulfuric acid, a brief history

Sulfuric acid has been known for centuries. Intitially, it was prepared by distilling ferrous sulfate ( green Vitriol) and collect the vapors. This was an ineffiecient process and sulfuric acid was quite expensive at this time. About the 18th century, a process was developed where sulfur was mixed with potassium nitrate and ignited in a bell jar with a dish with a small amount of water in it. This method had better yeilds but was still costly. This process was further developed into the lead chamber process where Nitrogen oxides and sulfur dioxide and water vapor where allowed to react in a lead line chamber. This made nitrosyl sulfate or chamber crystals which could be added to more water and the nitrogen oxides driven off by heat.

Lastly, in the early 20th century, the contact process was developed. A vanadium based catalyst is heated while sulfur dioxide and air are combine to form sulfur trioxide. This is lead through concentrated sulfuric acid to form "fuming sulfuric acid" which can then be dilute with water to again make more contentrated sulfuric acid.

Properties of sulfuric acid

Sulfuric acid is a strong acid that is a member of the mineral acid class. This class iincludes inorganic acids like nitric, hydrochloric, and phosphoric acids. It is very dense as the 98% acid is 1.84 times the density of water. It is viscous and extremely corrosive to skin, clothing, metals, and reactive with many chemicals generating heat, explosions, or toxic gases. The acid must be added to water and not vice versa as it generates a lot of heat on dilution and adding water to acid would cause spattering and splashing. Because of thi acids great affinity for water, it is an excellent dehydrating agent for drying gases and in organic sythesis.

Dilute sulfuric acid on metals

When sufficiently diluted with water, sulfuric acid acts as a normal strong acid liberating hydrogen gas and making the sulfate of the metal.

Ex: Fe(iron) + H2SO4 > FeSO4(iron sulfate) + H2(hydrogen); Zn(zinc) + H2SO4 > ZnSO4 + H2

Note: The dilute acid has no action upon copper, mercury, lead, silver, or gold


Hot concentrated sulfuric acid on metals

When the concentrated (>90%) sulfuric acid is heated though, it is a different chemical entirely. It acts like a moderately strong oxidizing agent. Because of this, when metals are heated with the acid, sulfur dioxide is given off instead of hydrogen as half of the acid is reduced by the metal.

Ex: Cu(copper) + 2H2SO4(hot) > CuSO4 + H2O+ SO2; Hg(mercury) + 2H2SO4(hot) > HgSO4 + H2O+ SO2

Note: This action works virtually on all metals exepted the most noble like platinum and gold

Sulfuric acid on bases and metal oxides and carbonates

Sulfuric acid behaving like a normal acid when dilute, will react with hydroxide bases like sodium hydroxide, potassium hydroxide, and ammonium hydroxide to make the corresponding sulfate and water with generation of heat. It is also active on carbonates of most metals as well as many oxides. Thus copper oxide can be converted to copper sulfate solution and cobalt carbonate, which is insoluble in water, is dissolved in sulfuric acid with effervesence giving cobalt sulfate solution and carbon dioxide gas.

Hot concentrated sulfuric acid on salts

Sulfuric acid is a strong protonating agent and it has a high boiling point. This is used in good effect by liberating other acids from there respective salts. For instance, plain rock salt(sodium chloride) gives off hydrogen chloride gas which is led into water to make hydrochloric acid. Another example is heating sodium nitrate and sulfuric acid and collecting the nearly 100 % nitric acid in a receiver flask.

Synthesis of Nitric acid

Sulfuric acid on organics

There are many, many uses for sulfuric acid in organic chemistry. Both as a catalyst and as a reagent. But the main organic reactions I will cover here are esterification and ether formation.

Esterfication is when and alcohol and an organic acid are combined with a sulfuric acid as a catalyst and heated to generate esters. Example would be ethyl alcohol and acetic acid to make ethyl acetate. The dehydrating properties of sulfuric acid drive the reaction to completion. Many esters have pleasant odors and are used in the food and fragrance industries.

Ether formation again relies on sulfuric acids dehydration properties but also it strong protonating abilites. as well. Here an alcohol is reacted with sulfuric acid to form an alkylsulfuric acid and more alcohol is added gradually with gentle heating with distillation. Example would be adding concentrated sulfuric acid to ethyl alcohol to make ethylsulfuric acid. The combination is put into a distiallion setup that has addition capabilites, and a slow stream of additional ethyl alcohol is added while the mixture is heated. The product, which is ethyl ether, is collected in a receiver flask.

Ethyl Ether synthesis

Root Sulfuric acid drain opener
Root Sulfuric acid drain opener | Source

Rooto drain opener- a cheap sulfuric acid alternative

If you are look for a cheap, technical grade concentrated sulfuric acid then Root drain opener might serve you well. It is essentially 96% sulfuric acid and as of 05/06/2012, the local Ace has it for roughly $22 per gallon. It has inhibitors and such but it still is useful as a dehydrating agent and liberating volatile acids.

Cheap Sulfuric acid Part I

Cheap sulfuric acid part 2

Electrolysis Experiments

Because sulfuric acid is a strong acid, it is also a strong electrolyte. In fact, it is this property which lends its use in automotive rechargeable batteries. That, and the fact it is cheap and widely available. There are many experiments using electrolytic cells one can perform with sulfuric acid. a dilute solution can electrolyzed with a sacrificial anode to make the sulfate salt of that metal. For instance, using an anode of copper and cathode also of copper, the copper anode begins to dissolve and form copper sulfate in solution. It is advised to separate the anode from the cathode with either a salt bridge set up or by gravity. Otherwise copper metal may deposit on the cathode to and extent that is short circuits to the anode possibly destroying the power supply.

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