Sodium hydroxide contamination

The most common strong base for titrating acidic analytes in aqueous solutions is NaOH. Sodium hydroxide is available both as a solid and as an approximately 50% w/v solution. Solutions of NaOH may be standardized against any of the primary weak acid standards listed in Table 9.7. The standardization of NaOH, however, is complicated by potential contamination from the following reaction between CO2 and OH . 

HBr reacts with metals, producing highly explosive hydrogen gas. If aleak or spill occurs, exposure to the vapors should be avoided. If a high concentration of aqueous acid is accidentally spilled, it should be diluted immediately with water to reduce fuming prior to neutralization. Hydrobromic acid may be neutralized with soda ash or lime sprinkled over the contaminated area. An aqueous solution of sodium hydroxide may also be used to neutralize the diluted acid. 

Sodium wire and finely sliced sodium are equally good to use in this reaction. It is important to avoid contamination of the sodium by surface action which converts part of it into sodium hydroxide. 

To a solution of 130 g. (0.6 mole) of arsanilic acid (Org. Syn. 3, 13) in 600 cc. (0.6 mole) of normal sodium hydroxide is added 52 g. (0.62 mole) of sodium bicarbonate and 70 g. (0.75 mole) of chloroacetamide (Org. Syn. 7, 16). The mixture is heated 011 a water bath to 90-1000 and a steady evolution of carbon dioxide occurs. At the end of two hours, when gas evolution has practically ceased, the mixture is cooled to 40° C., stirred vigorously and 150 cc. of 1 1 hydrochloric acid poured in rapidly. /i-Arsonophenylglycinamide crystallizes at once and, after cooling to room temperature, is filtered by suction and washed once with 2 per cent hydrochloric acid (Note 1), then with cold water. The crude product thus obtained is contaminated with some arsanilic acid and possibly other products. These are removed during purification. The crude product is suspended in about 400 cc. of water and with vigorous stirring, treated carefully with 25 per cent aqueous sodium hydroxide until solution is just complete. At this point the mixture is still acid to litmus and an excess of sodium hydroxide is to be avoided to prevent decomposition of the product. About 15 g. of boneblack... 

When such contaminated flour enters trade channels, either as such or in the form of prepared products, the finding of hair fragments is highly significant. Whether they may have come from the flour or have originated in a bakery or factory does not lessen their repugnance to the consumer. Recovered hairs are identified by means of their several characteristics. Some of the more salient are conspicuous intemodes and compound medulla of rat hairs, inconspicuous intemodes and smooth continuous medulla of cat hair, and differences discernible after treatment with 10% sodium hydroxide and after treatment with hypochlorite. 

For many years phenol was made on a large industrial scale from the substitution reaction of benzene sulfonic acid with sodium hydroxide. This produced sodium sulfite as a by-product. Production and disposal of this material, contaminated with aromatic compounds, on a large scale contributed to the poor economics of the process, which has now been replaced by the much more atom economic cumene route (see Chapter 2, Schemes 2.2 and 2.3). 

Competing reactions often consume some of the starting materials. For example, sodium metal reacts with water to produce sodium hydroxide. If a sample of oxygen is contaminated with water vapor, both O2 and H2 O will react with the sodium metal. The more water present in the gas mixture, the less Na2 O2 will be formed. 

Industrial wastewater often is contaminated with strong acids. Environmental regulations require that such wastewater be neutralized before it is returned to the environment. A 1.50x10" mL sample of wastewater was titrated with 0.1250 M sodium hydroxide, and 38.65 mL of the base was required to reach the stoichiometric point. What was the molarity of hydronium ions in this sample of wastewater ... 

Pretreatment of hair samples also includes an extraction, usually with an alkaline sodium hydroxide solution, followed by cleaning up with LLE with n-hexane/ethyl acetate. Instead of LLE, the employment of SPE is also possible. Furthermore, the solid phase microextraction (SPME) in combination with head-space analysis is usable [104-106]. In the case of using hair samples, possible external contamination (e.g., by passive smoking of Cannabis) has to be considered as false positive result. False positive results can be avoided by washing of the hair samples previous to extraction [107]. Storage of collected samples is another important fact that can cause false results in their content of A9-THC and metabolites [108-110]. 

Decontamination None needed in the field wash contaminated surfaces with a 5% solution by weight of sodium hydroxide in 95%... 

In the decomposer, deionized water reacts with the amalgam, which becomes the anode to a short-circuited cathode. The caustic soda produced is stored or evaporated, if higher concentration is required. The hydrogen gas is cooled by refrigeration to remove water vapor and traces of mercury. Some of these techniques are employed in different facilities to maximize the production of chlorine, minimize the consumption of NaCl, and also to prevent the buildup of impurities such as sulfate in the brine.26 The production of pure chlorine gas and pure 50% sodium hydroxide with no need for further concentration of the dilute solution is the advantage that the mercury cell possesses over other cells. However, the cell consumes more energy and requires a very pure brine solution with least metal contaminants and above all requires more concern about mercury releases into the environment.4... 

This type of electrolytic cell consists of anodes and cathodes that are separated by a water impermeable ion-conducting membrane. Brine is fed through the anode where chlorine gas is generated and sodium hydroxide solution collects at the cathode. Chloride ions are prevented from migrating from the anode compartment to the cathode compartment by the membrane and this, consequently, leads to the production of sodium hydroxide, free of contaminants like salts. The condition of the membrane during operation requires more care. They must remain stable while being exposed to chlorine and strong caustic solution on either side they must allow, also, the transport of sodium ions and not chloride ions. 

In early designs, the reaction heat was typically removed by cooling water. Crude dichloroethane was withdrawn from the reactor as a liquid, acid-washed to remove ferric chloride, then neutralized with dilute sodium hydroxide, and purified by distillation. The material used for separation of the ferric chloride can be recycled up to a point, but a purge must be taken. This creates waste streams contaminated with chlorinated hydrocarbons that must be treated prior to disposal. 

In an incident involving corrosive attack on aluminium by sodium hydroxide solution, the vigorous evolution of hydrogen was noticed before a tank trailer (supposed to be mild steel) had perforated [1], Corrosion caused failure of an aluminium coupling between a pressure gauge and a pump, causing personal contamination [2],... 

A chloroform-methanol mixture was put into a drum contaminated with sodium hydroxide. A vigorous reaction set in and the drum burst. Chloroform normally reacts slowly with sodium hydroxide owing to the insolubility of the latter. The presence of methanol (or other solubiliser) increases the rate of reaction by increasing the degree of contact between chloroform and alkali [1]. Addition of chloroform... 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Succinic anhydride is dimerised to 1,6-dioxaspiro [4.4] nonane-2,7-dione by heating with sodium hydroxide. Modification of an existing procedure by adding further sodium hydroxide after the initial reaction led to a severe exothermic reaction after heating for some 30 h which fused the glass flask to the heating mantle, probably at a temperature approaching 550°C. The reason for this was not known [1], At elevated temperatures and under influence of alkali, succinic acid condenses decarboxylatively beyond the dimeric spiroacetal, sometimes explosively. Contamination of the anhydride with base is to be avoided [2],... 

The residue from vacuum distillation of crude material (contaminated with sodium hydroxide) exploded after showing signs of decomposition. Experiment showed that 2-chloro-4-nitrotoluene decomposes violently when heated at 170-200° C in presence of alkali. Thorough water washing is therefore essential before distillation is attempted [1], A similar incident was reported with mixed chloronitrotoluene isomers [2],... 

Attempted disposal of a small amount of liquid chlorine by pouring it into 20% sodium hydroxide solution caused a violent reaction leading to personal contamination. 

Passage of thionyl chloride through a flexible metal transfer hose which was contaminated with water or sodium hydroxide solution caused the hose to burst. Interaction with water violently decomposes the chloride to hydrogen chloride (2 mol) and sulfur dioxide (1 mol), the total expansion ratio from liquid to gas being 993 1 at 20° C, so very high pressures may be generated. 

A survey, with many references, of 14 classes of preparative reactions involving hydrogen peroxide or its derivatives emphasises safety aspects of the various procedures [11]. Following the decomposition of 100 1 of 50% aqueous hydrogen peroxide which damaged the 630 1 stainless vessel rated at 6 bar, the effect of added contaminants and variations in temperature and pH on the adiabatic decomposition was studied in a 1 1 pressure vessel, where a final temperature of 310°C and a pressure around 200 bar were attained. Rust had little effect, but addition of a little ammonia (pH increased from 1.8 to 6.0) caused the induction period to fall dramatically, effectively from infinity to a few h at 40°C and a few min at 80°C. Addition of sodium hydroxide to pH 7.5 reduced the induction period at 24°C from infinity to about 4 min [12],... 

Accidental contamination of a metal scoop with flake sodium hydroxide, prior to its use with zinc dust, caused ignition of the latter [1]. A stiff paste prepared from zinc dust and 10% sodium hydroxide solution attains a temperature above 100°C after exposure to air for 15 min [2], The residue of zinc dust and sodium hydroxide solution from a lecture demonstration involving zinc plating a copper coin presents a high fire risk if discarded onto paper in a waste bin, ignition of the paper having occurred on many occasions. Dissolve the residue in dilute acid before flushing away with water [3],... 

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