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Prof. Haynes starts the programme by describing the free radical mechanism for the chlorination of methane. He points out that the variety of products formed in the reaction gives two problems, one... of analysis and one of separation. For some mixtures of liquid products, the problem of separating them can be solved by distillation and Prof. Haynes demonstrates and comments on both conventional and fractional distillation techniques. The problem of analysis can be solved using gas chromatography. Dr. Harding describes how this technique works and the way it can be applied to problems in industrial analysis, for example, the chlorination of methane. The programme takes the student into an industrial laboratory where the reaction between chlorine and methane is being studied by research chemists to find the optimum conditions for the preparation of the four products, methyl chloride, methylene dichloride, chloroform and carbon tetrachloride. The effect on product ratio of varying the proportion of chlorine and methane, is shown by gas chromatography. In the post broadcast notes the student is given the gas chromatograms obtained by the industrial chemists and asked to work out for himself the optimum conditions for producing any of the four chloromethanes. The remaining part of the programme is an introduction to infra-red spectroscopy. Prof. Haynes demonstrates an infra-red spectrophotometer and uses a model to show how the infra-red spectrum is recorded. He comments on the information that infra-red spectra can give about the structure of organic molecules and emphasises the importance of infra-red spectroscopy in the chemistry course.
Metadata describing this Open University video programme
Item code: S24-; 03
First transmission date: 12-02-1972
Published: 1972
Rights Statement:
Restrictions on use:
Duration: 00:24:26
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Producer: David Jackson
Contributors: Charles Harding; Len Haynes
Publisher: BBC Open University
Keyword(s): Analysis; Distillation; Free radical mechanism; Gas chromatography; Infra-red spectroscopy; Methane chlorination; Separation
Footage description: Len Haynes introduces the programme. He briefly reviews the process of photochemical chlorination of methane as discussed in the correspondence text. Products of the reaction are shown. Haynes explains the difference between photochemical chlorination of methane and the thermal industrial process. Haynes begins a demonstration of the industrial thermal process using a small scale laboratory set up. He points out the elements of the apparatus and explains their function, particularly the reaction vessel. The demonstration continues with film shots at an I.C.I. laboratory. The products of the reaction are again shown. Haynes with a flask containing the liquid products of a chlorination. He poses the questions - how many components are there and how can they be separated. Shots of drawings of some classical distillation processes. Haynes then demonstrates a simple distillation in the laboratory. Haynes next demonstrates the process of fractional distillation in the laboratory. He explains how the process works. Haynes explains why it is difficult to separate mixtures, using the fractional distillation process, which have elements whose boiling points are very nearly the same. Charlie Harding with a gas chromatograph explains a technique for separating small amounts of mixtures whose elements may have identical boiling points. He explains first, with the aid of models and diagrams, how the gas chromatograph works. Harding also demonstrates the technique. Shots of the chromatograph readings. The industrial application ot gas chromatography for the separation of the products of methane chlorination is demonstrated with film shots of an industrial laboratory. The results are shown on chart paper. Commentary by Harding explains what is happening. Len Haynes with an infra-red spectrophotometer explains and demonstrates how the products of methane chlorination are identified after separation. Haynes then uses a simplified model of the infra-red spectrophotometer to explain how the instrument works. Haynes lists some other uses of infra-red spectrophotometry.
Master spool number: 6LT/70310
Production number: 00521_2167
Videofinder number: 1720
Available to public: no