Sodium carbonate, standard

In the second method a solution of the approximate strength required is prepared, and this is standardised against some standard alkaline substance, such as sodium tetraborate or anhydrous sodium carbonate standard potassium iodate or pure silver may also be used (see Section 10.84). If a solution of an exact strength is required, a solution of an approximate strength somewhat greater than that desired is first prepared this is suitably diluted with water after standardisation (for a typical calculation, see Appendix 17). 

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. 

A quantitative analysis for NH3 in several household cleaning products is carried out by titrating with a standard solution of HGl. The titration s progress is followed thermometrically by monitoring the temperature of the titration mixture as a function of the volume of added titrant. Household cleaning products may contain other basic components, such as sodium citrate or sodium carbonate, that will also be titrated by HGl. By comparing titration curves for prepared samples of NH3 to titration curves for the samples, it is possible to determine that portion of the thermometric titration curve due to the neutralization of NH3. 

Tin ores and concentrates can be brought into solution by fusing at red heat in a nickel cmcible with sodium carbonate and sodium peroxide, leaching in water, acidifying with hydrochloric acid, and digesting with nickel sheet. The solution is cooled in carbon dioxide, and titrated with a standard potassium iodate—iodide solution using starch as an indicator. 

In the AWWA specification standards, technical soHd sodium chlorite should not contain less than 78.0 wt % NaC102. The impurity limits for 80% assay sodium chlorite should not be more than 17.0 wt % sodium chloride, 3.0 wt % sodium carbonate, 3.0 wt % sodium sulfate, and 0.0003 wt % arsenic. The AWWA standards also specify the analysis procedures for all of the chemical components ia the sodium chlorite. 

The sodium carbonate content may be deterrnined on the same sample after a slight excess of silver nitrate has been added. An excess of barium chloride solution is added and, after the barium carbonate has setded, it is filtered, washed, and decomposed by boiling with an excess of standard hydrochloric acid. The excess of acid is then titrated with standard sodium hydroxide solution, using methyl red as indicator, and the sodium carbonate content is calculated. 

Discussion. The hydroxides of sodium, potassium, and barium are generally employed for the preparation of solutions of standard alkalis they are water-soluble strong bases. Solutions made from aqueous ammonia are undesirable, because they tend to lose ammonia, especially if the concentration exceeds 0.5M moreover, it is a weak base, and difficulties arise in titrations with weak acids (compare Section 10.15). Sodium hydroxide is most commonly used because of its cheapness. None of these solid hydroxides can be obtained pure, so that a standard solution cannot be prepared by dissolving a known weight in a definite volume of water. Both sodium hydroxide and potassium hydroxide are extremely hygroscopic a certain amount of alkali carbonate and water are always present. Exact results cannot be obtained in the presence of carbonate with some indicators, and it is therefore necessary to discuss methods for the preparation of carbonate-free alkali solutions. For many purposes sodium hydroxide (which contains 1-2 per cent of sodium carbonate) is sufficiently pure. 

Calculation. The weight of anhydrous sodium carbonate, Na2C03, which has reacted with the standard hydrochloric acid can be readily calculated from the equation ... 

The method may be applied to commercial boric acid, but as this material may contain ammonium salts it is necessary to add a slight excess of sodium carbonate solution and then to boil down to half-bulk to expel ammonia. Any precipitate which separates is filtered off and washed thoroughly, then the filtrate is neutralised to methyl red, and after boiling, mannitol is added, and the solution titrated with standard 0.1M sodium hydroxide solution ... 

Thermogravimetry is a valuable technique for the assessment of the purity of materials. Analytical reagents, especially those used in titrimetric analysis as primary standards, e.g. sodium carbonate, sodium tetraborate, and potassium hydrogenphthalate, have been examined. Many primary standards absorb appreciable amounts of water when exposed to moist atmospheres. TG data can show the extent of this absorption and hence the most suitable drying temperature for a given reagent may be determined. 

Standard solution of silica. Fuse 0.107 g of pure, dry precipitated silica with 1.0 g of anhydrous sodium carbonate in a platinum crucible. Cool the melt, dissolve it in de-ionised water, dilute to 500 mL, and store in a polythene bottle. 1 mL = 0.1 mg Si. Dilute as appropriate, say, to 1 mL = 0.01 mg Si. 

Wash solutions for precipitates, 426 Washing of precipitates 118, 426 by decantation. 119 solubility losses in, 119, 427 Washing soda D. of sodium carbonate in, 295 Water absorbents for, 477 ammonia-free, 679 deionised, 90 D. of hardness, 332 D. of total cation concentration, 210 D. with Karl Fischer reagent 637 distilled, 90 high purity, 91 ionic product of, 36 types and standards for, (T) 90 volume of 1 g at various temperatures, (T)87... 

Sodium Thiosulfate. A 0.00250 N solution was made by dissolving 0.63 gram of sodium thiosulfate and 0.10 gram of sodium carbonate per liter of freshly boiled water. It was standardized each day against approximately 0.00300 N potassium iodate solution. 

Consider as an example the standardization of a solution of hydrochloric acid by titration against a weighed amount of sodium carbonate. The strength of the hydrochloric acid will be computed from... 

Xie [39] determined trace amounts of chlorophenols and chloroguaiacols in marine sediments collected off the Swedish coast. The compounds were desorbed from sediment surfaces by a mixture of acetic anhydride and hexane, after buffering with O.lmol L 1 sodium carbonate. The optimal pH was achieved by a 1 4 ratio of buffer to acetic anhydride. The acetylated extracts were analysed by glass capillary gas chromatography with electron capture detection. The recoveries, at the pg kg-1 level, ranged from 85-100% with standard deviations of 4-11%. 

In a standardization experiment, 0.4920 g of primary standard sodium carbonate (Na2C03) was exactly neutralized by 19.04 mL of hydrochloric acid solution. What is the molarity of the HC1 solution Refer to Equation (4.7) for the reaction involved. 

Primary standard sodium carbonate may also be used to standardize acid solutions. Sodium carbonate also possesses all the qualities of a good primary standard, like KHP and THAM. When titrating sodium carbonate, carbonic acid, H2C03, is one of the products and must be decomposed with heat to push the equilibria below to completion to the right ... 

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