What are chemicals?

Chemicals are all chemical compounds produced by chemical processes in the lab or industrially. They can be pure substances or mixtures of substances. Although there are different definitions asserting that the term “chemicals” describes all chemical elements and their compounds. Here, however, chemicals should only be understood as chemical substances that are involved in chemical reactions.

Chemicals are divided into organic and inorganic chemicals. Organic chemistry covers practically all the carbon-containing compounds, while inorganic chemistry (inorganic matter) relates to the other elements of the periodic table and their compounds. Petrochemicals are a subsection of organic chemistry. Petrochemicals are chemical products derived from crude oil and natural gas. These chemicals are extracted during the refining process when crude oil or gas is distilled or cracked.

Organic chemicals include aromatics, alcohols (e.g. ethanol), acetates, alkenes, amines, nitriles, sulfates, phosphates and esters. Some of the primary petrochemicals obtained in the process mentioned above include benzene, ethylene, propylene and toluene. Inorganic chemicals include acids and bases, e.g. sulfuric acid and ammonia.

Grades of purity of chemicals

Chemicals are usually offered in various grades of purity. The purity of a substance refers to the ratio of a desired substance to the total mixture of substances. The American Chemical Society grades the purity of chemicals as follows (from low to high), but the exact specification depends on the manufacturer and material:

  • Technical 
  • Purified 
  • Lab 
  • N.F. 
  • U.S.P. 
  • Reagent
  • A.C.S. 

Purity plays a vital role in the chemicals trade, where a distinction is made between technical chemicals (low purity) and fine chemicals (high purity). Technical chemicals are also called heavy chemicals when referring to inorganic and organic base chemicals that are produced in large quantities and are of technical grade (e.g. sodium hydroxide, sulfuric acid or ethylene). These heavy chemicals (also called base or basic chemicals) contrast with high-purity fine chemicals, which are produced in smaller batches. The latter are used in chemical synthesis in laboratories, as food additives or as raw materials in the production of pharmaceutical agents, e.g.

State of aggregation of chemicals

The physical state of a substance is called a state of aggregation. A chemical’s state of aggregation depends on the properties of the substance, the temperature, and the ambient pressure. Chemistry defines three classic states of aggregation – solid, liquid and gaseous:

  • Solid: A substance usually retains both its shape and volume; material density is highest here. Examples: polystyrene, molybdenum
  • Liquid: the volume is retained, but the shape is variable and adapts to the surrounding space; a solid differs from its liquid form by a higher material density of 5% to 10%. Examples: methanol, sulfuric acid
  • Gaseous: both volume and dimensional are unstable; their density is almost 1,000 times smaller than that of solids. Examples: 1.2 butadiene, ethylene, ammonia

A chemical’s state of aggregation engenders different requirements for its storage, among other things.

Chemical compatibility

Furthermore, chemical substances react in different ways when they come in contact with each other. The relative degree to which a material may contact another without causing corrosion, degradation or adverse change of properties is called chemical compatibility: If substances mix and do not change, they are considered compatible, if they mix and change or do not mix at all are considered incompatible. Therefore, storing and handling chemicals on the same premises requires utmost care and attention to avoid any chemical reaction hazards. The single most important rule is to separate incompatible materials which, if accidentally mixed, could cause a fire, an explosion, or the generation of toxic gases. As a general rule, incompatible chemicals should be stored in separate tank pits. The tanks have to be clearly labeled to indicate what product is stored therein. As a first rough outline to judge compatibility, chemicals may be grouped as follows:

  • Flammable liquids
  • Compressed gases
  • Volatile hazardous substances
  • Acids
  • Liquid bases
  • Liquid oxidizers
  • Non-volatile liquid hazardous substances

To guarantee proper chemical compatibility, tank terminals take reference from the US Coast Guard Compatibility Chart. It comprises a total 43 groups which then are classified into Reactive Groups and Cargo Groups. When a new product is to be stored in a designated tank, the compatibility chart indicates whether the new product is compatible with the existing products stored in the same tank pit.

These aspects also play a key role in the REACH Regulation (Regulation (EC) No. 1907/2006 concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals). For instance, registration involves submitting a chemical safety report, which describes the effect of the substance on people and the environment and based on this contains an assessment of the risk involved in using the substance. In the case of “hazardous” substances, the substance properties and any risk management measures must be compiled in a safety data sheet and forwarded throughout the supply chain.

To assess whether a substance is classified as hazardous, REACH explicitly refers to the criteria of the CLP Regulation (Regulation (EC) No. 1272/2008 on classification, labelling and packaging of substances and mixtures). The CLP Regulation has been in force since January 20, 2009 and implements the United Nations’ Globally Harmonized System of Classification and Labelling of Chemicals (GHS) into European law. The GHS is an international standards system for classifying chemicals, as well as labeling them on packaging and in safety data sheets.

Status: December 2015
All information subject to change. Errors and omissions excepted.

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