Chemical Reactivity of Copper
Copper is a transition metal known for its distinctive reddish-brown colour and excellent electrical and thermal conductivity. In terms of chemical reactivity, copper is considered a relatively unreactive metal, positioned below hydrogen in the activity series. This means it is less reactive than many common metals such as iron, zinc, or aluminium.
Reaction with Water
Copper does not react with water, whether cold, hot, or in the form of steam, under normal conditions. This inertness towards water is one of the reasons why copper pipes have been extensively used for plumbing in various parts of the world, including India, for centuries. Its resistance to water corrosion ensures the longevity and purity of water supplied through such systems.
Reaction with Air
Copper reacts slowly with components in the air. When exposed to dry air, it tarnishes very slowly, forming a thin, protective layer of reddish-brown copper(I) oxide (Cu₂O). This initial layer helps prevent further oxidation.
However, in moist air containing carbon dioxide, copper undergoes a more noticeable change over time. It develops a characteristic green layer known as patina. This patina is primarily composed of basic copper carbonate (CuCO₃·Cu(OH)₂), and sometimes basic copper sulfate in industrial areas. This green layer is famously seen on ancient copper artefacts, temple roofs in South India, or bronze statues (bronze being a copper alloy), providing a protective barrier against further corrosion of the underlying metal. This process is very slow and can take many years to become prominent.
Toxicity
Copper is an essential trace element for all living organisms, including humans. It plays crucial roles in various biological processes, such as enzyme functions, iron metabolism, and nerve function. Small amounts of copper are necessary for health. For instance, storing water in copper vessels, a traditional practice in some Indian households, is believed to leach beneficial quantities of copper into the water.
However, while essential, excessive intake of copper can be toxic. High concentrations of copper can lead to symptoms affecting the liver, kidneys, and gastrointestinal tract. The human body has mechanisms to regulate copper levels, but these can be overwhelmed by very high exposures. Therefore, while not inherently toxic in necessary amounts, copper compounds can be harmful in large doses.
Radioactivity
Naturally occurring copper is not radioactive. It consists predominantly of two stable isotopes: copper-63 and copper-65. There are no naturally occurring radioactive isotopes of copper. While artificial radioactive isotopes of copper can be produced in laboratories for specific scientific or medical applications, these are not found naturally and do not contribute to the element’s inherent properties.
Flammability
Bulk copper metal, such as copper wires, sheets, or utensils, is non-flammable. It does not ignite or burn in air under normal conditions. Copper’s high melting point (1085 °C) further contributes to its resistance to combustion. However, like many other metals, very fine copper powder can be combustible or explosive when dispersed in air and exposed to an ignition source. This is a characteristic of finely divided materials due to their large surface area, but it is not representative of copper in its common forms.
Famous Chemical Reaction Involving Copper
A classic example of a chemical reaction involving copper is its reaction with silver nitrate solution. This is a single displacement reaction where copper, being more reactive than silver, displaces silver from its salt solution.
When a copper wire or strip is placed into a solution of silver nitrate (AgNO₃), the copper slowly dissolves, and silver metal begins to deposit on the surface of the copper in the form of shiny crystals or dendrites. Simultaneously, the colourless silver nitrate solution gradually turns blue, indicating the formation of copper(II) nitrate (Cu(NO₃)₂).
The chemical equation for this reaction is:
Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)
This reaction vividly demonstrates the relative reactivity of metals and is a common experiment in chemistry laboratories.