C3: Chemicals in Our Lives - Risks & Benefits
Welcome to this overview of Chemistry Module C3.You can take a quiz on this module by clicking here.
Like many countries, the UK has resources such as salt, coal and limestone deposits buried deep underground. In the UK they were mainly discovered in the North-West, which has lead to a large and successful chemical industry in that area.
The movement of tectonic plates has caused the Earth to look very different now from what it was like in the past. Geologists study rocks to determine how old an area might be and what the surface might have looked like, although they can never be certain on an answer because of course nobody was around to see it! They study mountains, erosion, sedimentation, dissolving and evaporation. Sometimes they also use magnetic clues on rocks but more commonly the things in or on rocks can give more information, such as:
Fossils or shell fragments Ripple patterns (proof of rivers, streams) The shape of grains
A geologist at work studying rocks
Chemically knows as sodium chloride, salt is used for many things such as flavouring and preserving food, melting ice on roads during winter or as a source of chemicals. It is important to know the risks of salt for this course, which includes eating too much of it which raises blood pressure and causes circulatory problems. Someone with a high blood pressure should pick food with a lower salt content. The Food Standards Agency is responsible in the UK for monitoring chemicals in food - including salt - and advising the public on what to eat and how much of it.
Salt can be extracted from the sea or underground mines in the following methods:1) Evaporating the water from seawater to leave salt, used for food Positives: produces lots of salt, easy and cheap Negatives: long process, better in warm climates2) Rock salt mining*, used on roads Positives: produces lots of salt Negatives: difficult and expensive, requires large machinery3) Solution mining**, used for chemical industry and food preservation Positives: easy to do, produces brine to preserve food Negatives: expensive, requires large machinery, lengthy process
*Rock salt mining involves mining underground with the large machinery. **Solution mining involves pumping water underground where the salt dissolves into the water making a solution which then is pumped back up to the surface.
An alkali is a compound that is soluble in water and has a higher pH level than 7. They are often used to neutralise acidic solids, or make soaps, bind dyes to cloth, and make glass. They were previously made by burning wood or urine, but new methods emerged in the Industrial Revolution when the demand for alkalis increased.
The Lelanc process was the first of these new methods in the 1700s which made alkali from salt and limestone heated with coal. This process produced a large amount of waste, including acidic hydrogen chloride gas which caused acid rain. Solid waste also produced hydrogen sulphide gas which released a foul smell as it decomposed. Overall it produced more waste product than useful product, and the reactants were very expensive, so an alternative was needed.
The modern process for producing alkali is called electrolysis which produces valuable chemicals hydrogen and chlorine as well as much needed alkali sodium hydroxide. The process involves putting an electric current through brine (salt solution) which causes the solution to break up and create the products...
Sodium Hydroxide: an important alkali used for making soaps, detergents, drain cleaners, paper and textiles. The risk is it is a corrosive substance. Hydrogen: a gas used for hydrocarbon fuels, making margarine and ammonia. In future it will be used as an alternative to power cars. However, it is very flammable. Chlorine: used in bleaches and, previously, water supplies to remove bacteria. As a gas it is very toxic when inhaled, and has been used in wars because of this.
A diagram of an electrolysis cell.
Chemical industries are regulated to make sure that they dispose of waste products correctly and safely and that any products are not harmful to humans and the planet. They may have direct implications to humans, or be hazardous in the long run because they take a long time to decompose, can be carried a long way by the wind or rivers, or can accumulate in food chains. The assessment of damage is based on the chance of being hurt by it and the consequences of being hurt by it. People are more likely to take risks with only short term effects than long term, and when they have a choice rather than being forced.
Assessment takes place around the life cycle of a product which has four phases: making the material from natural raw materials, manufacture, use and disposal. Each phase is assessed on the amount of energy used, used resources, and the obtaining and disposal of materials in each phase. The purpose of the life cycle assessments (LCA) is to consider the most sustainable method.
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