Calcium carbonate reaction with weak acid

The equations that represent the reactions with water support the prediction that NH4NO3 dissolves to form an acidic solution and Na3P04 dissolves to form a basic solution. Calcium chloride is the salt of a strong base-strong acid, so neither ion reacts with water and the solution is neutral. Both ions in ammonium hydrogen carbonate react with water. Because Kt, for HCOs" is greater than for NH4, the salt dissolves to form a weakly basic solution. 

The production of salts of aldonic acids by the action of chlorine in the presence of small amounts of bromide or iodide was patented by the Chemische Fabrik vorm. Sandoz. The solution was kept alkaline with sodium carbonate, alkali being added during the reaction to prevent the loss of bromine vapor. This reaction apparently involves an oxidation by bromine, the chlorine serving as an indirect oxidant, as in the method of Ling and Nanji. In the latter method a slow stream of chlorine is passed into a buffered weakly acidic solution of bromide and calcium carbonate. 

For weakly acidic systems (pH 5-6) in which the accumulation of hydrobromic acid is prevented by buffering agents such as calcium carbonate or benzoic acid salts, more information is available. Isbell and Pigman have made an extensive study of such systems, including a thorough consideration of the effect of the concentration of total bromine, free bromine, hypobromous acid and bromide ion on the velocity of the reaction. The results very definitely showed a direct correlation between free bromine concentration and the velocity of the oxidation. No such correlation could be found with hypobromous acid. The results are shown in Tables VII and VIII. The velocity constants were determined for a- and for 8-D-glucose. In the table for /S-D-glucose, in experiments 2 and 5, the hypobromous acid concentration varied 1 10 but the reaction rate varied 1 3. The variations in free bromine concentration follow the variations in the reaction rate constants and the kf values are based on the assumption that free bromine is the oxidant. The concentration of the oxidant (a in equation 31) is therefore the concentration of free bromine. 

Chemically speaking, limestone is calcium carbonate. Although calcium carbonate is insoluble in water, it does dissolve in a weakly acidic solution. Surface water is weakly acidic, because carbon dioxide in the air dissolves in rain and reacts with the water to form carbonic acid. As the acidic surface water percolates through the ground, it converts insoluble calcium carbonate to soluble calcium hydrogen carbonate. When we heat water, we reverse this reaction, causing deposits of what amounts to limestone to build. 

Calcium carbonate, which is present in limestone and marble, is another water-insoluble solid that is soluble in strong and weak acids. Here the solid produces a low concentration of C03 ions, which combine with H to form the weak acid H2CO3. This causes more of the solid to dissolve, and so on. Carbonic acid, H2CO3, is a very unstable substance that decomposes into H2O and C02(g). The net ionic equation for the reaction of CaC03 with an acid is given below. 

Neutralization Acidic or basic wastewaters must be neutrahzed prior to discharge. If an industry produces both acidic and basic wastes, these wastes may be mixed together at the proper rates to obtain neutral pH levels. Equahzation basins can be used as neutralization basins. When separate chemical neutralization is required, sodium hydroxide is the easiest base material to handle in a hquid form and can be used at various concentrations for in-line neutralization with a minimum of equipment. Yet, lime remains the most widely used base for acid neutr zation. Limestone is used when reaction rates are slow and considerable time is available for reaction. Siilfuric acid is the primary acid used to neutralize high-pH wastewaters unless calcium smfate might be precipitated as a resmt of the neutralization reaction. Hydrochloric acid can be used for neutrahzation of basic wastes if sulfuric acid is not acceptable. For very weak basic waste-waters carbon dioxide can be adequate for neutralization. 

Directions a) Determine by testing with litmus paper whether solutions of the following salts show a neutral, acidic, or basic reaction sodium chloride, potassium nitrate, sodium sulphate, calcium chloiide, sodium sulphide, copper sulphate, ferric chloride, sodium carbonate, and sodium acetate. (1) Tabulate the results and state in the case of each salt the strength (weak or strong) of the acid and the base from which the salt is derived. 

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