Sodium carbonate, 5.28

Crystallized Sodium Carbonate, Na2CO3T0H2O, from Anhydrous Sodium Carbonate 

Soda ash is commercial anhydrous sodium carbonate. When a solution saturated at boiling temperature is allowed to cool to below 33°, a transparent crystalline mass separates of the formula Na2CC 3-10H2O, known commercially as soda crystals or sal soda. 

If water is evaporated from the solution, saturated at 100°, a solid of the composition Na2C03-H20 separates. Besides the dekahydrate and monohydrate there is at least one other well-recognized hydrate, the heptahydrate, 

Na2C03-7H20. This compound separates from solution only over a narrow range of temperature and concentration. 

The curves in Fig. 15 show the different hydrated forms which are in equilibrium with the saturated solution at different temperatures. It will be seen that the dekahydrate is the stable hydrate only below 33°. In the following preparation, if barely enough water to form the dekahydrate were added to the anhydrous soda ash and the mixture heated to 100°, a complete solution would not be obtained because some monohydrate would separate. Enough water, therefore, is taken to hold all the monohydrate in solution at the boiling point. When this solution cools to below 33° it may become highly supersaturated with the dekahydrate unless a few crystal fragments of the dekahydrate are added. It occasionally happens that if no seed crystals are added the heptahydrate 

The drying of sodium carbonate is important in the standardization of acids for various types of acidimetrtc titrations. The recommended drying temperature range is 250-30Q-C although Duval (22) stated that a horizontal mass level was obtained from 100-840 C. In a more recent study, Newkirk and Aliferis (23) found that the decomposition temperature of anhydrous 

When the sodium carbonate was heated in platinum or gold sample holders, the mass-loss was much less rapid and was probably due to the decomposition of the sample to form sodium oxide and carbon dioxide. As seen in curve 6y the presence of a nitrogen gas stream resulted in a faster rate of mass-loss, while when water was present (curve 7) the observed mass-loss rate was less. A sample of sodium carbonate dried at 350°C showed no further mass change on further heating for 12 hours at 600°C and 4 hours at 650°C in a platinum crucible in air. The reaction of sodium carbonate with coarse silica sand occurred rapidly at 800-850°C as shown by curve 9. On grinding the silica mixture, the first evidence of mass-loss was at about 500°C (curve 70) or somewhat less than the temperature in curve 9. 

It was recommended that sodium carbonate for analytical use be dried by heating in dry air or carbon dioxide using a platinum or other inert sample container in the temperature range of 250 to at least 700°C. 

CHEMICAL NAME = sodium carbonate CAS NUMBER = 497-19-8 MOLECULAR FORMULA = Na2C03 MOLAR MASS = 106.0 g/mol COMPOSITION = Na(43.4%) C(11.3%) 0(45.3) 

MELTING POINT = 85 BOILING POINT = decomposes DENSITY = 2.5 g/cm3 

LeBlancs method uses sulfuric acid and common salt to initially produce sodium sulfate, Na2S04. Sodium sulfate is then reacted with charcoal and limestone to produce sodium carbonate and calcium sulfide  

The sodium carbonate and calcium sulfide were separated by mixing with water. Because sodium carbonate was soluble in the water and calcium sulfide was insoluble, the former would be suspended in solution. 

The LeBlanc process was the principal method of producing soda ash until 1860 when the Belgian Ernest Solvay (1838-1922) developed the process that bears his name. The Solvay process, sometimes called the ammonia method of soda production, uses ammonia, NH3, carbon dioxide, and salt to produce sodium bicarbonate (baking soda), NaHC03. Sodium bicarbonate is then heated to give soda ash. The series of reactions representing the Solvay process are  

Magnesium ions are removed from the crude brine as a precipitate of magnesium hydroxide by adding milk of lime (or caustic soda). Calcium ions are removed by the addition of either sodium carbonate solution, or by injecting carbon dioxide in the form of combustion gases. 

The ammonia-soda process [31.21, 31.22], is a long-established route for the production of soda ash (Na2C03), washing soda (Na2C03 IOH2O) and sodium bicarbonate (Na2HC03), as well as several co-products (including caustic soda, calcium chloride and ammonium chloride). Despite intense competition from natur- 

The primary raw materials are purified saturated brine (see section 31.18) and high-calcium limestone. The overall simplified equation is  

However, because of the low solubility of the calcium carbonate, the reaction does not proceed as shown. Ammonia is, therefore, used to drive the process, which consists of seven stages. 

Limestone is calcined (usually in a mixed feed kiln — see section 16.4.3 — using coke as fuel) to produce quicklime (used in stage 6) and an exhaust gas rich in carbon dioxide (used in stage 3). 

BOILING point Not applicable begins to decompose below melting point 

Humans have known about and used sodium carbonate for thousands of years. The ancient Egyptians extracted the compound from a mineral known as natron found in dry lake 

Sodium carbonate. Red atoms are oxygen black atom is carbon and turquoise atoms are sodium. Gray stick indicates double bond. 

The product of this reaction is a dark ashy material that contains sodium carbonate, calcium sulfide, carbon dioxide, and other byproducts  

The sodium carbonate is extracted from this mixture and purified. The Leblanc invention was one of the great breakthroughs in the early years of chemical science. It made possible, among other things, the mass production of soap for the first time in human history. 

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Heavy metals often can be removed effectively by chemical precipitation in the form of carbonates, hydroxides, or sulfides. Sodium carbonate, sodium bisulfite, sodium hydroxide, and calcium oxide are all used as precipitation agents. The solids precipitate as a floe containing a large amount of water in the structure. The precipitated solids need to be separated by thickening or filtration and recycled if possible. If recycling is not possible, then the solids are usually disposed of to a landfill. 

Equation V-64 is that of a parabola, and electrocapillary curves are indeed approximately parabolic in shape. Because E ax tmd 7 max very nearly the same for certain electrolytes, such as sodium sulfate and sodium carbonate, it is generally assumed that specific adsorption effects are absent, and Emax is taken as a constant (-0.480 V) characteristic of the mercury-water interface. For most other electrolytes there is a shift in the maximum voltage, and is then taken to be Emax 0.480. Some values for the quantities are given in Table V-5 [113]. Much information of this type is due to Gouy [125], although additional results are to be found in most of the other references cited in this section. 

Qualitative examples abound. Perfect crystals of sodium carbonate, sulfate, or phosphate may be kept for years without efflorescing, although if scratched, they begin to do so immediately. Too strongly heated or burned lime or plaster of Paris takes up the first traces of water only with difficulty. Reactions of this type tend to be autocat-alytic. The initial rate is slow, due to the absence of the necessary linear interface, but the rate accelerates as more and more product is formed. See Refs. 147-153 for other examples. Ruckenstein [154] has discussed a kinetic model based on nucleation theory. There is certainly evidence that patches of product may be present, as in the oxidation of Mo(lOO) surfaces [155], and that surface defects are important [156]. There may be catalysis thus reaction VII-27 is catalyzed by water vapor [157]. A topotactic reaction is one where the product or products retain the external crystalline shape of the reactant crystal [158]. More often, however, there is a complicated morphology with pitting, cracking, and pore formation, as with calcium carbonate [159]. 

On standing, gelatinous aluminium hydroxide, which may initially have even more water occluded than indicated above, is converted into a form insoluble in both acids and alkalis, which is probably a hydrated form of the oxide AI2O3. Both forms, however, have strong adsorptive power and will adsorb dyes, a property long used by the textile trade to dye rayon. The cloth is first impregnated with an aluminium salt (for example sulphate or acetate) when addition of a little alkali, such as sodium carbonate, causes aluminium hydroxide to deposit in the pores of the material. The presence of this aluminium hydroxide in the cloth helps the dye to bite by ad sorbing it—hence the name mordant (Latin mordere = to bite) dye process. 

Carbon dioxide is used in the manufacture of sodium carbonate by the ammonia-soda process, urea, salicyclic acid (for aspirin), fire extinguishers and aerated water. Lesser amounts are used to transfer heat generated by an atomic reactor to water and so produce steam and electric power, whilst solid carbon dioxide is used as a refrigerant, a mixture of solid carbon dioxide and alcohol providing a good low-temperature bath (195 K) in which reactions can be carried out in the laboratory. 

A soluble silicate—a trioxosilicate— is obtained when silica is fused with sodium carbonate ... 

Iodine has the lowest standard electrode potential of any of the common halogens (E = +0.54 V) and is consequently the least powerful oxidising agent. Indeed, the iodide ion can be oxidised to iodine by many reagents including air which will oxidise an acidified solution of iodide ions. However, iodine will oxidise arsenate(lll) to arsenate(V) in alkaline solution (the presence of sodium carbonate makes the solution sufficiently alkaline) but the reaction is reversible, for example by removal of iodine. 

Sodium dichromate is prepared on the large scale by heating powdered chromite with sodium carbonate, with free access of air the sodium chromate first formed is treated with acid ... 

Fusion of a manganese compound with sodium carbonate and potassium nitrate (on porcelain) gives a green manganate(VI) (p.. 86)... 

The normal carbonate CuCOj is not known two naturalls occurring basic carbonates have already been mentioned. If a solution of, for example, sodium carbonate is added to a solution of a copper(II) salt, a green basic carbonate is precipitated the reactions are ... 

Any solid mercury compound when fused with sodium carbonate yields a grey deposit of mercury. (Caution mercury vapour is formed.)... 

Ethyl bromide soon distils over, and collects as heavy oily drops under the water in the receiving flask, evaporation of the very volatile distillate being thus prevented. If the mixture in the flask A froths badly, moderate the heating of the sand-bath. When no more oily drops of ethyl bromide come over, pour the contents of the receiving flask into a separating-funnel, and carefully run oflF the heavy lower layer of ethyl bromide. Discard the upper aqueous layer, and return the ethyl bromide to the funnel. Add an equal volume of 10% sodium carbonate solution, cork the funnel securely and shake cautiously. Owing to the presence of hydrobromic and sulphurous acids in the crude ethyl bromide, a brisk evolution of carbon dioxide occurs therefore release the... 

Required Monochloroacetic acid, 50 g. anhydrous sodium carbonate, 30 g. sodium nitrite, 36-5 g. 

Reactions of Picric Acid, (i) The presence of the three nitro groups in picric acid considerably increases the acidic properties of the phenolic group and therefore picric acid, unlike most phenols, will evolve carbon dioxide from sodium carbonate solution. Show this by boiling picric acid with sodium carbonate solution, using the method described in Section 5, p. 330. The reaction is not readily shown by a cold saturated aqueous solution of picric acid, because the latter is so dilute that the sodium carbonate is largely converted into sodium bicarbonate without loss of carbon dioxide. 

SULPHANILAMIDE. (Reaction C.) Add 15 g. of the above thoroughly drained sulphonamide to 10 ml. of concentrated hydrochloric acid diluted with 20 ml. water, and boil the mixture gently under reflux for i hour. Then add 30 ml. of water and heat the mixture again to boiling, with the addition of a small quantity of animal charcoal. Filter the boiling solution, and add powdered sodium carbonate in small quantities to the filtrate with stirring until all eflFervescence ceases and the sulphanilamide is precipitated as a white powder. Cool the mixture thoroughly and filter oflF the sulphanilamide at the pump, wash with water and dry. Yield, ca. 10 g. 

Required Aniline, 20 ml. hydrochloric acid, 50 ml, sodium nitrite, 17 g. sodium carbonate (anhydrous) 17 g. sodium sulphite (7H2O), 115 g... 

Required Anthranilic acid, 20 g. anhydrous sodium carbonate, 7 5 g, sodium nitrite, 12 g. concentrated hydrochloric acid, 190 ml. crystalline copper sulphate, 50 g. concentrated ammonia, 85 ml, hydroxylamine hydrochloride, 14-5 g. (or hydroxylamine sulphate, 17-4 g.) acetic acid, 10-20 ml,... 

A) Diazotisation of Anthranilic Acid, Dissolve 20 g. of anthranilic acid in a solution of 7 5 g. of anhydrous sodium carbonate in 200 ml. of water contained in a 400 ml. beaker, (The mixture may be warmed very gently with stirring to obtain a solution more rapidly, and then cooled.) Add slowly 12 g. of sodium nitrite and cool the stirred solution below 10 , Pour this cold solution slowly on to a vigorously stirred mixture of 40 ml, of concentrated hydrochloric acid and 120 g. of crushed ice in a 600 ml. beaker. 

Required Anhydrous sodium carbonate, 2 g. sulphanilic acid, 7 g. sodium nitrite, 2-2 g. hydrochloric acid, 12 ml. dimethylaniline, 4 ml. 

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