toxicity and toxicology

I.Randi Caustic Soda

Generality

Caustic soda - or sodium hydroxide - is a highly basic substance used in many areas.

Caustic soda is commercially available in solid form, but also in the form of solutions at different concentrations. It is a reagent widely exploited both at industrial and domestic level, as it is widely used in research laboratories of various types (chemical laboratories, chemical-pharmaceutical laboratories, etc.).

Although it can also be purchased by private individuals for domestic use, due to its dangerousness, the use of caustic soda requires special precautions and knowledge.

Did you know that ...

The term "caustic" comes from the Greek καυστικός (kaustikòs) which literally means "burning".

What is that

What is Caustic Soda?

Caustic soda is the common name used to refer to the chemical compound having a brute formula NaOH . This compound, more correctly called "sodium hydroxide", is a strong base that - as can easily be deduced from its very name - is able to exert a marked caustic action when it comes into contact with certain living materials and fabrics.

In some cases, caustic soda is also improperly defined as "sodium hydrate", "sodium hydrate" or "sodium hydrate".

Please note

Caustic soda should not be confused with " soda ", a common name used to indicate a completely different chemical compound, namely sodium carbonate (Na2CO3). In fact, this last compound is the sodium salt of carbonic acid and not a strong base as, instead, is sodium hydroxide.

Features

What are the main features of caustic soda?

Caustic soda is a solid compound at room temperature, but highly hygroscopic (ie it is able to absorb the moisture contained in the air) and, consequently, deliquescent .

In other words, due to its remarkable ability to absorb the humidity present in the air (hygroscopic properties), the caustic soda changes its physical state usually to liquid (deliquescence phenomenon).

However, caustic soda is an odorless white solid. Normally, in the solid state it is found in the form of flakes or pearls.

Another characteristic of caustic soda is that of producing heat when it is placed in water. The dissolution of sodium hydroxide in water, in fact, is strongly exothermic, so that the temperature reached during this operation can even exceed 95 ° C. The caustic soda solutions are generally colorless, clear or sometimes slightly turbid and, depending on the amount of sodium hydroxide they contain, they have a more or less basic pH.

Caustic soda is not soluble only in water, but also in ethanol (or ethyl alcohol, if you prefer). The dissolution of the caustic soda in ethanol is even more dangerous than that in water, this because the strong heat that is released during the dissolution of the substance can even cause the vapors of ethyl alcohol to ignite (remember, in fact, that ethanol is a very volatile substance).

Purposes

What are the uses of caustic soda?

As mentioned, caustic soda is a compound used both at an industrial and domestic level and can be used in many areas, from cooking to cosmetics.

Industrial uses

In an industrial environment, caustic soda is used as a reagent in numerous chemical reactions, but it can also be used as an additive. In detail, caustic soda is used:

  • To synthesize paints and dyes ;
  • For the synthesis of sodium hypochlorite, the main component of the well-known bleach;
  • For the regeneration of ion exchange resins (special resins used in demineralization and water purification processes);
  • To carry out the saponification reaction, therefore for the production of some types of soap (for example, Marseille soap, Aleppo soap, etc.).
  • In the food industry, where it is used as an acidity regulator and as a synthetic technological adjuvant . In this context, caustic soda is used, for example, for the industrial preparation of caramel and pretzels, to deamarize the olives and as a food additive in snacks, jellies and sweets. The caustic soda used as a food additive is indicated on the label with the abbreviation E524 .
  • In the wine industry, where it is used in the form of solutions for cleaning the tanks.
  • In the cosmetic industry, where it is used as a pH regulating agent. In this context, caustic soda is used, for example, in products for beard, depilatories and various detergents. Usually, in the list of ingredients shown on cosmetic products, caustic soda is indicated with the name "Sodium Hydroxide".
  • In the chemical-pharmaceutical industry, as a pH regulator.
  • In the electronics and electrical engineering industry for the production of circuits.

Domestic uses

Caustic soda is also used in the home, especially to unclog sinks, showers, tubs, toilets etc., therefore, to unclog domestic drains . However, this practice is not very recommended, both for the danger deriving from the handling of the caustic soda, and because - if not adequately diluted - sodium hydroxide could damage the pipes.

However, in addition to this type of use, caustic soda can also be used in the domestic environment for:

  • Clean grills and barbecues;
  • Clean the tanks used in the craft production of wine;
  • Wood stripping;
  • Produce handmade soap, using it to saponify various types of vegetable oils and fats.

Although caustic soda can also be sold to private individuals and can be used in the aforementioned domestic activities, we remind you again that the use of this substance involves a series of potential risks and that, therefore, it must be carried out with extreme caution and with all precautions of the case.

Disposal

How is Caustic Soda Disposed?

The caustic soda and its solutions must not be thrown into the sewers or into the environment, but must be disposed of in accordance with the regulations in force in special waste collection points.

In case of doubt, therefore, it is necessary to contact the supplier of the waste management services in your area, or contact companies specialized in the disposal of similar chemical products.

Warnings and Safety

The companies producing caustic soda, together with the product, must provide a safety data sheet (SDS) which contains the warnings and all information on the chemical-physical, toxicological and environmental hazard properties of the chemical produced. This information is necessary to be able to handle and use caustic soda correctly and safely.

Among the various data present in the safety data sheet which must also be present on the label, we recall the risk phrases and the classification of the product according to the EC regulation 1272/2008.

In the specific case of caustic soda, the risk phrase reported is " R35: Causes severe burns " and the substance is classified as " Corrosive " and accompanied by the corresponding hazard pictogram (see figure).

This pictogram indicates that the chemical compound in question - therefore, in this specific situation, caustic soda - can be corrosive to metals and causes severe skin burns and serious eye damage.

In addition to the aforementioned information, the safety data sheet must also contain information on the manufacturing company, information concerning the handling and storage of the product, information on first aid measures, fire prevention measures and measures to be taken in the event of environmental release and information concerning the transport and disposal of the product.

Precautions for use

What precautions should I take before using Caustic Soda?

Given the dangerousness of the product, it is of fundamental importance to take precautions and precautions before and during the use of caustic soda.

Below are some indications on the precautions and preventive measures that must be taken before and during the handling of sodium hydroxide:

  • Avoid direct contact with caustic soda and always wear suitable protective clothing (gloves, glasses, mask, lab coat, long-sleeved shirts, closed shoes and long trousers);
  • When preparing a caustic soda solution, gradually add small amounts of sodium hydroxide to the water and NOT vice versa. The strongly exothermic reaction between caustic soda and water would be excessively violent if the procedure was carried out in reverse, that is if the water was added to the caustic soda. Furthermore, in order to optimize the dissolution process, it is advisable to place the container in which the solution is prepared in a bath of water and ice.
  • Store the caustic soda tightly closed in a cool, dry place.
  • Avoid contact with metals such as zinc, tin and aluminum, as caustic soda is corrosive to these substances, particularly when it is in the presence of moisture.
  • Attention to contact with ammonium salts (since caustic soda reacts with these compounds releasing ammonia), with acids (exothermic reaction) and with metals (hydrogen release).

Please note

Wearing protective clothing is of fundamental importance when using caustic soda.

In fact, contact of skin and mucous membranes with sodium hydroxide can cause second, third and even fourth degree burns; contact with eyes can cause serious injury; ingestion of caustic soda causes strong corrosion of the oral cavity and pharynx with the risk of perforation of the esophagus and stomach and inhalation of dust or vapors causes lacerations of the tissue of the nasal mucosa and upper respiratory tract.

Emergency Advice

What to do in case of Contact with Caustic Soda

Given the high basicity and the consequent high corrosive power of the caustic soda, in case of contact with eyes, skin or mucous membranes, in case of inhalation and / or in case of ingestion, it is necessary to immediately call the sanitary assistance and go to the nearest first aid .

However, pending the arrival of emergency medical personnel or the doctor, some operations must be carried out in order to remove the caustic soda that has come into contact with it from the body. Therefore, some useful first aid tips to put into practice in case of accidents with caustic soda will be reported below.

  • In case of contact of caustic soda with clothes, remove them immediately and wash the body with plenty of water. Of course, before any re-use, clothing that has come into contact with caustic soda must be washed.
  • In case of contact with the skin, wash immediately with plenty of water and soap, rinsing carefully.
  • In the event of contact with the eyes, wash immediately with plenty of running water keeping the eyelid open (in laboratories and in the industries there are special emergency eyewashes for this kind of situation).
  • If swallowed, immediately rinse your mouth with water, but DO NOT induce vomiting.

Regardless of the type of contact with caustic soda (with clothes, skin, mucous membranes, etc.), the speed of intervention is fundamental in order to limit damage; just as it is essential to immediately contact the doctor or the emergency room immediately after putting into practice the aforementioned first aid advice.