Many controversial issues revolve around complex scientific arguments which can be better understood with at least a minimal knowledge and understanding of the chemical reactions and processes going on in the world around us. This textbook offers an accessible introduction to chemical principles and concepts, and applies them to relevant environmental situations and issues. Written for students who have not taken A' level chemistry, this book bridges the gap between GSCE chemistry and first year undergraduate level.
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The structure of the atom and the properties of the proton, neutron and electron
The stability of the nucleus, radioactivity and the properties of emitted particles
The mole and its use
Electronic structures of atoms
Structure of the Periodic Table
Elementary chemical bonding theory
Water as a solvent, and LowryâBrønsted acids and bases
Oxidation and reduction. The use of oxidation numbers
The erosion of York Minster, UK
York Minster is over 500 years old and requires very expensive maintenance to ensure its existence for future generations. It is composed of a wide variety of materials, which have been subjected to erosion. The external fabric of stone has been eroded both by natural weathering and by chemicals put into the atmosphere by manâs actions (Figure 1.1). Winning the battle between the Minster and its environment lies not only in reducing atmospheric pollution but also in the replacement of damaged stone. This replacement is not a simple matter because, although there is fresh stone in abundance, the continual replacement of stone can undermine the integrity of a building by causing the structure to become unstable. At York Minster the stonemasons try, as far as possible, to incorporate all old stone into any repair work because there is the danger that if too much fabric is replaced there could be a serious loss of authenticity (Brimblecombe and Bowler 1990).
What chemicals then have caused the erosion of the stone?
The pollutants sulphur dioxide (SO2), nitrogen oxides (NOx) and ozone (O3) are believed to be the main culprits. Although York Minster has suffered from anthropogenic effects, there is no method by which these effects can be readily separated from other contributions such as poor construction techniques, wrongly chosen materials, natural weathering and biological attack. The rate of destruction can be significantly increased during heavy rainfall if vast quantities of water containing pollutants percolate through the stone carrying away any reaction products in the run off (Baer and Snethlage 1997). The reaction products are mainly salts which are formed by the reaction of negatively charged anions (e.g.
from pollutant gases or acids, with positively charged cations in the stone (e.g. Ca2+).
Figure 1.1 Stone erosion York Minster 2000. (above) An eroded vestibule buttress on the Chapter House (north side of York Minster). (below) The same buttress after restoration.
Source: Reproduced with permission from Mr S. Mills.
York Minster is made of mainly two types of stone: a crystalline, granular dolomite, MgCO3.CaCO3, and a more porous, granular oolithic limestone made largely of calcite, CaCO3. As construction materials, the dolomite stone is much more resistant to erosion than the limestone (Mills 2000), lasting up to four times longer.
In the presence of water, sulphur dioxide reacts with dolomite limestone as follows,
Dry oolithic limestone reacts with sulphur dioxide and oxygen thus,
Again, the presence of water leads to the formation of hydrated calcium sulphate.
The calcium sulphate (gypsum), produced in the above reactions is much more soluble in water than the stone from which it is derived and consequently more is lost as a result of solution in rainwater. Solid crystalline gypsum also has a more open structure, which leads to an increase in volume of about 100 per cent. The result is an increase in internal pressure that causes cracks to develop together with crumbling and bursting of the stone.
Whilst it is true that sulphur dioxide emissions in York have greatly declined since the 1950s, the stone decay continues. Why this is so remains unclear. It may be linked with ozone and nitrogen oxide concentrations at ground level caused by emissions from vehicles (Haneef et al. 1990). There is, for example, strong evidence to suggest a synegetic effect between sulphur dioxide and nitrogen oxides, which enhances stone corrosion (Haneef et al. 1990). Here sulphuric acid together with nitrogen oxide (nitrogen monoxide) are formed,
SO2(g) + NO2(g) + H2O(l) = H2SO4(aq) + NO(g)
Nitrogen oxides (NOx) are known to form nitric acid with water which will react with limestone to form the much more soluble salt calcium nitrate, Ca(NO3)2. However, studies made on York Minster have found no evidence that NOx gases have had any direct effects on limestone decay (Cook and Gibbs 1996).
The effects of atmospheric pollutants on limestone decay are complex and there are a number of uncertainties concerning the reliance of one chemical on the presence of another in order for enhanced corrosion to take place. What is certain is that, since the Industrial Revolution and the corresponding increase in atmospheric pollution, the rate at which York Minster stone has eroded has substantially increased.
What is environmental chemistry?
It is clear from the opening section that chemistry is a discipline much involved in the study of human interaction with the environment. Chemistry is the study of the composition, structure and properties of materials and how they undergo chemical and physical changes. Environmental chemistry is the study of those changes that have had an effect on both living organisms and non-living matter in the environment.
Chemicals have a poor reputation! Some are known to be a source of pollution and many are hazardous if used incorrectly. However, it is important to realise that all forms of matter in our environment whether synthetic or natural are made of chemicals. Many materials in common use such as paper, cloth, plastics, metals, etc. have undergone some form of chemical treatment and change during their manufacture, and will probably undergo more change before they become waste.
There are many ways in which humans and other living organisms are exposed to chemicals such as detergents, paints, drugs, exhaust fumes, industrial effluents, pesticides, natural toxins in plants and animals, etc. in their everyday existence. When chemicals are a main source of pollution, then that pollution is usually caused by human error, lack of understanding and knowledge, greed, or by inefficient technology. Chemicals may well be the cause of a number of environmental problems but it is also the use of chemicals that often provides the answers to those problems. Many chemicals are dangerous but many are also beneficial! There is no doubt that, without chemicals and the chemical industry, human life would be far less enjoyable.
A revision of the elementary classification of matter
Matter can be classified by the state it is normally found in, i.e. as a solid, liquid or gas. These states are called the phases of matter.
The connections between the three main phases of matter can be established by examination of what happens to water when it is cooled and heated. At a temperature of â10 °C (Celsius) and 1 atmosphere pressure, pure water exists as ice (Figure 1.2, point A). If it is heated to a temperature of 0 °C (A to B), at 1 atmosphere pressure, ice will start to melt and become liquid water. Its temperature will remain constant at 0 °C until all the ice has melted (B to C). Thus water has a melting point of 0 °C at 1 atmosphere pressure. If the pressure is kept constant and the heating continued until the temperature reaches 100 °C (C to D), the liquid water will start to boil and invisible gaseous water or steam is formed. Again, the temperature will remain constant until all of the liquid water has been turned into a gas (D to E). Water has a boiling point of 100 °C at 1 atmosphere pressure. Continued heating will only make the steam hotter (E to F).
Figure 1.2 Temperature vs time graph for water heated at a constant rate.
If steam at 200 °C and 1 atmosphere pressure is cooled down (F to E), it will start to form a liquid at 100 °C. Its temperature will remain the same until all the steam has liquefied or condensed (E to D), and then it will cool down further (D to C) until solid ice starts to form. This will occur at 0 °C, the solidification or freezing point. The temperature of the liquid/solid mixture will remain at 0 °C until all of the water has solidified/undergone freezing (C to B). Cooling down to a temperature below 0 °C then involves no further phase change (B to A).
Evaporation is different from boiling. When liquid water is placed in an open container at room temperature, evaporation will occur from its surface until there is none left. The liquid changes into a gas which, because it is formed below the boiling point, is known as a vapour. When water is warmed, the rate of evaporation from its surface is increased. At its boiling point, liquid water is turned into bubbles of gaseous water inside liquid and not just at its surface. Water vapour therefore exists over liquid water at all times up to and including its boiling point. It is identical to steam except it is much cooler and, like steam, is invisible.
Sublimation occurs when matter changes from solid to g...
Table of contents
Cover Page
Title Page
Copyright Page
Series editorsâ preface Environmental Science titles
Preface
Acknowledgements
1 Some basic chemical concepts
2 More advanced chemical concepts: energy, entropy and rates of reaction
