Sulphuric Acid and Its Salts

Properties of Sulphuric Acid. (Perform the experiments in a fume cupboard ) Interaction of Concentrated Sulphuric Acid with Water. Pour 10-15 ml of water into a beaker, measure its temperature, and without extracting the thermometer, add 2 ml of a 96% solution of sulphuric acid. Record the thermometer readings. In what sequence must water and concentrated sulphuric acid be poured together to prepare solutions of various concentrations  

Action of Sulphuric Acid on Organic Substances. 1. Immerse a splinter into a test tube containing a small amount of concentrated sulphuric acid. What occurs  

Prepare 2-3 ml of a sulphuric acid solution (1 1). Wet the tip of a glass rod with this solution and make an inscription on a sheet of white paper. Carefully heat the paper to dry it. What happens What properties of sulphuric acid do the above experiments indicate  

Put 10 g of powdered sugar into a 50-ml beaker, wet it with water until a thick paste forms, and then add 3-5 ml of concentrated sulphuric acid. Rapidly stir the contents with a glass rod and see what happens. What gaseous substances are obtained  

Action of Sulphuric Acid on Non-Metals. Pour 2-3 ml of a 96% sulphuric acid solution into each of two test tubes, introduce a small piece of sulphur into one of them and coal into the other, and carefully heat them. What occurs Write the equation of the reaction. 

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Aqueous solutions of thiosulphuric acid and its salts are not very stable, but tend to decompose, yielding sulphurous and polythionic acids and a deposit of sulphur. The decomposition may take place in at least three different ways 3... 

This same substitution of sulphur for oxygen occurs in the case of cyanic acid and its salts, e.g., potassium thio-cyanate and ammonium thiocyanate used as reagents in testing for ferric iron. 

The sulphonation of organic compounds to produce a sulphonic acid or a salt can be performed using a wide variety of reagents, including sulphuric acid and its derivatives, sulphur trioxide, sulphur dioxide, sulphites and hydrogen sulphites. These are all discussed below. 

Formic acid and its salts when heated with concentrated sulphuric acid, are decomposed, and carbon monoxide is formed. The presence of the latter can be shown by the fact that the gas produced burns with a blue flame. 

The affinity of sulphuric acid for most bases is stronger than that of all other acids. In a red heat, phosphoric and boracic acids, being fixed in the fire, expel sulphuric acid from its salts. In solution, sulphate of lime is decomposed by oxalic and racemic acids, which seize the lime and sulphate of potash, by tartaric, racemic, and perchloric acids, which combine with the potash. In other circumstances, however, the sulphuric acid appears stronger than the acids just mentioned thus, it decomposes phosphates in the cold, and tartrates, or perchlorates, with the aid of a gentle heat. 

This acid is formed when selenium is dissolved in nitric acid, and the solution evaporated to dryness. It is a solid which, when heated, is converted into a yellow gas, condensing again into acicular crystals. It is very soluble in water, and Iras an acid taste. In composition it corresponds to sulphurous acid. This latter acid and its salts deprive selenious acid audits salts of oxygen, causing the selenium to be deposited in the uncombined state. 

Berzelius supposed that the water in isethionic acid and its salts exists in the form of ether (C H + H O = C H 0), and hence alcohol and ether contain different radicals. In a letter to Magnus, Berzelius did not accept the view that the compounds contain ethylene and sulphuric acid it follows of necessity that it must be assumed that the hydrogen and oxygen which one acid contains more than the other are combined in a way different from an additional atom of water. ... 

Tests on sulphuric acid, sulphamic acid and its salts... 

Equip a 1-litre three-necked flask with a powerful mechanical stirrer, a separatory funnel with stem extending to the bottom of the flask, and a thermometer. Cool the flask in a mixture of ice and salt. Place a solution of 95 g. of A.R. sodium nitrite in 375 ml. of water in the flask and stir. When the temperature has fallen to 0° (or slightly below) introduce slowly from the separatory funnel a mixture of 25 ml. of water, 62 5 g. (34 ml.) of concentrated sulphuric acid and 110 g. (135 ml.) of n-amyl alcohol, which has previously been cooled to 0°. The rate of addition must be controlled so that the temperature is maintained at 1° the addition takes 45-60 minutes. AUow the mixture to stand for 1 5 hours and then filter from the precipitated sodium sulphate (1). Separate the upper yellow n-amyl nitrite layer, wash it with a solution containing 1 g. of sodium bicarbonate and 12 5 g. of sodium chloride in 50 ml. of water, and dry it with 5-7 g. of anhydrous magnesium sulphate. The resulting crude n-amyl nitrite (107 g.) is satisfactory for many purposes (2). Upon distillation, it passes over largely at 104° with negligible decomposition. The b.p. under reduced pressure is 29°/40 mm. 

The residue in the flask will contain the sodium (or potassium) salt of the acid together with excess of alkali. Just acidify with dilute sulphuric acid and observe whether a crystalline acid separates if it does, filter, recrystallise and identify (Section 111,85). If no crystaUine solid is obtained, the solution may be just neutralised to phenolphthalein and the solution of the alkali salt used for the preparation of a crystaUine derivative. This wiU confirm, if necessary, the results of hydrolysis by method 1. If the time factor is important, either method 1 or the product of the caustic alkali hydrolysis may be used for the identification of the acid. 

In a 500 ml. bolt-head flask, provided with a mechanical stirrer, place 70 ml. of oleum (20 per cent. SO3) and heat it in an oil bath to 70°. By means of a separatory funnel, supported so that the stem is just above the surface of the acid, introduce 41 g. (34 ml.) of nitrobenzene slowly and at such a rate that the temperature of the well-stirred mixture does not rise above 100-105°. When all the nitrobenzene has been introduced, continue the heating at 110-115° for 30 minutes. Remove a test portion and add it to the excess of water. If the odour of nitrobenzene is still apparent, add a further 10 ml. of fuming sulphuric acid, and heat at 110-115° for 15 minutes the reaction mixture should then be free from nitrobenzene. Allow the mixture to cool and pour it with good mechanical stirring on to 200 g. of finely-crushed ice contained in a beaker. AU the nitrobenzenesulphonic acid passes into solution if a little sulphone is present, remove this by filtration. Stir the solution mechanically and add 70 g. of sodium chloride in small portions the sodium salt of m-nitro-benzenesulphonic acid separates as a pasty mass. Continue the stirring for about 30 minutes, allow to stand overnight, filter and press the cake well. The latter will retain sufficient acid to render unnecessary the addition of acid in the subsequent reduction with iron. Spread upon filter paper to dry partially. 

In a 1 5 or 2-Utre rovmd-bottomed flask, prepare cuprous chloride from 105 g. of crystallised copper sulphate as detailed in Section 11,50,1. Either wash the precipitate once by decantation or filter it at the pump and wash it with water containing a httle sulphurous acid dissolve it in 170 ml. of concentrated hydrochloric acid. Stopper the flask loosely (to prevent oxidation) and cool it in an ice - salt mixture whilst the diazo-tisation is being carried out. 

For this series of compounds qualitative information is quite extensive. Application of the criteria discussed in 8.2, in particular comparison with the corresponding methyl quaternary salt, establishment of the rate profile for nitration in sulphuric acid, and consideration of the encounter rate and activation parameters, shows that 2,4,6-collidine is nitrated as its cation. The same is true for the 3-nitration of 2,4- ... 

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