manufactors and use of chemicals

Alkalis
1. An alkali is a compound that dissolves to give a solution with a pH higher than 7
2. Before industrialisation in the 1700s, alkalis were still needed for a number of uses:
  1. Converting oils and fats into soap
  2. Making glass
  3. Neutralising acidic soils
  4. Making chemicals that bind natural dyes to cloth.
3. Traditional sources of alkalis to enable these processes included burnt wood (potash) and stale urine (ammonia). Alkalis contain an important property that allows them to neutralise acids.
  1. When this happens a salt is made. acid + alkali → salt + water
4. Reactions of alkalis- Higher tier
  1. Common examples of alkalis include soluble hydroxides and carbonates. When each of these alkalis reacts with an acid, there is a difference in the products that are formed.
    1. When an alkaline hydroxide reacts with an acid, salt and water are formed. This is shown by the general equation:
      1. Alkaline hydroxide + acid → salt + water
      2. For example
        Sodium hydroxide + hydrochloric acid → sodium chloride + water
        When an alkaline carbonate reacts with an acid, salt and water are again formed but there is also a third product, carbon dioxide
        Alkaline carbonate + acid → salt + water + carbon dioxide
        Calcium carbonate + sulfuric acid → calcium sulfate + water + carbon dioxide
        Note how the name of the salt is found - the first part of the name comes from the metal in the alkali used, the second comes from the acid used.
Making alkalis
1. Due to increased industrialisation in the 1700s there was a shortage of alkali. This led to the need for manufacture on a large scale.
2. The LeBlanc process
  1. This was a process invented to make alkali sodium carbonate on a large scale. Sodium chloride was mixed with sulfuric acid before being heated with charcoal and limestone.
  2. The process itself was very polluting. It released huge volumes of an acid gas (hydrogen chloride) into the air that wrecked the surrounding land. It also produced large amounts of solid waste that slowly released the toxic gas hydrogen sulfide. This gas has a characteristic smell of rotten eggs.
Waste into useful chemicals
1. The effect of pollution from this industry became very extensive. This pressured the government into taking action.
2. The industry was required to reduce the level of hydrogen chloride gas released into the atmosphere. The first response was to dissolve the hydrogen chloride in water, creating hydrochloric acid that at the time had no use.
3. A more useful method of disposal was discovered. Hydrogen chloride could be oxidised to form chlorine, a useful chemical by mixing it with oxygen and passing the mixture over a hot copper containing catalyst.
Water treatment
1. Water that has been contaminated with certain types of microorganisms can be very unsafe. It can cause diseases such as typhoid, cholera and dysentery.
2. Treating water with chlorine kills microorganisms that may exist in domestic water supplies. Chlorination of water began in the early part of the twentieth century, having a dramatic effect of reducing many waterborne diseases and so increasing public health.
3. There may be disadvantages of consuming water that has been treated with chlorine. When water is treated with chlorine some disinfection byproducts called tirhalomethanes (THMs) can form. They form when chlorine reacts with naturally occurring organic matter such as leaves.
4. There is a notion that THMs can cause cancer, although no firm evidence has been found to support this theory.
Electrolysis of brine
1. Brine is a solution of sodium chloride (NaCl) and water (H2O). The process of
  1. electrolysis involves using an electric current to bring about a chemical change and make new chemicals. The electrolysis of brine is a large-scale process used to manufacture chlorine from salt. Two other useful chemicals are obtained during the process, sodium hydroxide (NaOH) and hydrogen (H2).
    1. t is important that the chlorine and sodium hydroxide produced in the process are separated they react when they come into contact with each other.
2. Uses in industry
  1. The products of the electrolysis of brine have important uses in industry. Some of these uses are in the table below, but there are many more:
    1. Product of electrolysis of brine
      1. chlorine
        disinfectant and purifier manufacture of hydrochloric acid making plastics
      2. sodium hydroxide
        processing food products removing pollutants from water manufacture of paper
      3. hydrogen
        manufacture of hydrochloric acid potential as a pollution-free fuel

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