Truck and Track Autumn 2024 www.truckandtrack.com 58 DANGEROUS GOODS In this issue, our Dangerous Goods Columnist, Ali Karim FRSC CChem provides our readers an insight into the dangers of reactivity when incompatible materials come into contact while in the Supply Chain – especially with Oxygen and Oxidising Agents. As an Applied Chemist who spent my career in Industrial Chemistry with a few years sabbatical as a Chemistry and Physics Teacher, I would often conjecture that chemical reactivity is a by product of ‘matter’ attaining ‘stability’. And when we consider matter and its stability, we must reference our understanding of atomic structure(s). Fundamentally we must recall the negatively charged electrons (and their ‘shells’ or ‘energy levels’) as they orbit the protons and neutrons held tightly within the nucleus. Sometimes, stability is attained when two (or more) atoms combine to form one (or more) molecules which is termed covalency; while at other times, it comes from a transfer of negatively charged electrons from the outer shells/energy levels which can be termed an ionic reaction. When it comes to the latter, we must consider the meaning of Oxidation or Reduction Reactions, as well when both occur in the same reaction - we term a Redox Reaction. Consider Rusting – a chemical reaction that requires water and oxygen to covert elemental Iron into molecular Iron (III) Oxide. 4Fe + 3O2 + 6H2O → 4Fe(OH)3 Oxidation is used to describe a loss of electrons. It can also be used to describe a gain of oxygen. Reduction is used to describe the gain of electrons. It can also be used to describe a loss of oxygen. An oxidising agent causes another species to be oxidised (lose electrons) and is itself reduced as it gains the electrons. A reducing agent causes another species to be reduced (gain electrons) and is itself oxidised as it loses the electrons. When the iron reacts with oxygen, each iron atom loses three electrons, forming an iron ion represented as Fe3+. The iron has been oxidised in this process and has therefore acted as the reducing agent. The iron has also been oxidised because it has gained oxygen to become (the more stable) iron (III) oxide. When oxygen reacts with iron, each oxygen atom receives two electrons, forming an oxide ion representing as O2-. The oxygen has been reduced and has therefore acted as the oxidising agent. Iron Oxide is far more stable as a molecule that elemental Iron or elemental/molecular Oxygen. Rusting is the reaction process that Iron and Oxygen (in the presence of water) undergoes to become more stable – namely a molecule that is Iron (III) Oxide. Background to Oxygen Oxygen in the periodic table is a highly reactive non-metal, and an oxidizing agent that readily forms oxides (such as Rust) with most elements as well as with other compounds. By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element bind to form di-oxygen, a colourless and odourless di-atomic gas with the formula O2. Di-atomic oxygen gas constitutes 20.8% of the Earth’s atmosphere. The composition of the air that surrounds us – Gas Chemical Symbol % Nitrogen N2 78.084 Oxygen O2 20.947 Argon Ar 0.934 Carbon Dioxide C02 0.0350 Others Noble Gases etc Trace As a compound (including its oxides), the element Oxygen makes up almost half of the Earth’s crust. The name oxygen was coined in 1777 by Antoine Lavoisier, who first recognised oxygen as a chemical element and correctly characterized the role it plays in combustion. Common societal uses of gaseous and liquified Oxygen include production of steel, plastics and textiles, brazing, welding and cutting of metals, rocket propellant, oxygen therapy, life support systems in aircraft, submarines, spaceflight, cleaningsubstrates and diving – and essential in chemical reactions (as an additive/substrate). It must be absent for certain manufacturing, food packaging or preservation processes to prevent oxidation reactions. The Hazards of Unplanned Reactivity within the DG Supply Chain by Ali Karim Ali Karim TRUCK & TRAILER SOLUTIONS WELCOME TOALLPORTS GROUP allportsgroup.co.uk
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