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Revision notes: Revision of qualitative chemical tests
CHEMICAL ANALYSIS & IDENTIFICATION TESTS Doc Brown's Chemistry Qualitative Methods of Analysis Revision Notes PART 1 INTRODUCTION and chemical identification test index (repeated on each page) Introduction to qualitative analysis tests to identify inorganic gases & ions (cations/anions) and organic molecule functional groups Note - Chemical Calculations and Quantitative Analysis Index QUALITATIVE CHEMICAL TEST INDEX
Part 2 Qualitative tests to identify organic molecule functional groups of homologous series Part 3 TESTS for Metal cations (positive ions), metal carbonates, ammonium ion, hydrogen ions (acids) Part 4 TESTS for Gases, water and non–metallic elements Part 5 TESTS for Anions (negative ions) including hydroxide (alkalis) APPENDIX 1. IDENTIFYING ELEMENTS from LINE SPECTRA (non-chemical test method) PART 1 INTRODUCTION to CHEMICAL TESTS and ANALYSING SUBSTANCES Of what use is chemical analysis and chemical testing? Well, rather a lot, as it happens! The production of many products we use in our society involved some kind of chemical analysis at some stage or other. It might analysing mineral ores for their metal content or testing the final purity of some drug/medicine from the pharmaceutical industry. For chemical analysis analysts have developed a wide range of qualitative tests to detect specific chemicals which may be molecules or ions. Chemical tests are based on reactions that produce a gas with distinctive properties, or a colour change produced by adding a reagent or the production of an insoluble solid that appears as a precipitate. Modern instrumental methods provide a fast, sensitive and accurate means of analysing chemicals, and are particularly useful when the amount of chemical being analysed is small. Forensic scientists and drug control scientists rely heavily on such instrumental methods in their work. Environmental agencies monitor levels of oxygen and pollutants in rives and lakes. Hospitals carry out complex blood analysis for iron, proteins, cholesterol etc. and this is very important diagnostic information for clinicians and doctors seeking to get you well again prevent diseases developing. Blood can be analysed for specific proteins to indicate particular medical conditions e.g. cancer, and ions such as sodium, chloride and iron compounds. At water treatment plants test are done to determine the levels of metal ions, insecticides and lots of other substances to check that their levels are not high enough to be harmful to humans. Apart from a multitude of forensic tests for DNA, powder burns from guns, explosives etc. the police use breathalyser kits to test for alcohol levels in your breath and may request a blood sample for analysis too. Elements and compounds can be detected and identified using instrumental methods which are accurate, sensitive and rapid and are particularly useful when the amount of a sample is very small There are two types of chemical analysis Qualitative tests and quantitative analysis. Whatever the nature of the investigation, all tests of analyses should be carried out by using 'tried and tested' standard procedures. They should be the most accurate, reliable and safest methods that can be devised. It means, whatever laboratory you work in, anywhere in the world, you should get the same results as long as the sample is collected, stored and analysed by the same standard procedures. (a) QUALITATIVE CHEMICAL ANALYSIS Qualitative chemical analysis indicates whether a particular substance is present or not. It does not tell how much of the substance is there or its concentration. However, if a substance is potentially harmful, even toxic, its a good idea to know whether the substance is there at all. The larger the sample you have, the better. With more to work with you are more likely to able to detect minute traces of substances with qualitative tests AND have spare material to repeat tests several times if the results seem uncertain at first. At school/college level, the simple tests you learn enable to identify the cation (+ve ion e.g. metal ions) and anion (-ve ion, e.g. chloride, sulfate) in a salt, and the salt usually does contain only two ions, but some salts do have three ions e.g. iron(II) ammonium sulfate which might take a bit of sorting out. Most tests at this level are done on soluble substances so that you can dissolve the substance in water and carry out tests on the aqueous solution. Aqueous means a solution in water. You may come across a non-aqueous solution using a non-aqueous solvent like alcohol or hexane. AND don't forget, negative test results are just as important as positive results, you may need to eliminate possibilities as well as confirm the presence of a particular ion or gas etc. UNFORTUNATELY, not all tests are unique for a particular ion, but this shouldn't be a problem in school chemistry! Associated qualitative analysis links See index at top of page Typical qualitative tests are described in Parts 2 to 5. Summary of some cation and anion tests for GCSE/IGCSE/O Level students (b) QUANTITATIVE CHEMICAL ANALYSIS Quantitative analysis gives you (hopefully) a precise measure of how much of a substance is present or its concentration in a sample being analysed e.g. ore analysis tells you whether it is worth exploiting for a metal, the purity of drug ensure no harmful impurities in it, blood sample analysis for alcohol allows the police to decide to prosecute for 'being over the limit'. With a large sample you have spare material to repeat the quantitative analysis several times to get the most statistically valid result. In schools and colleges you can do quite accurate titrations to illustrate quantitative analysis. Associated quantitative links % purity of a product (GCSE/IGCSE/O level, introduction for Advanced Level) Volumetric titration analysis methods and calculations (GCSE/IGCSE/O level, introduction for Advanced Level) Various non-redox titration methods and questions (Advanced Level, acid-alkali, EDTA, silver nitrate etc.) Various redox titration methods and questions (Advanced Level, potassium manganate(VII), thiosulfate/iodine etc.) Other Associated Qualitative or Quantitative Analysis LINKS (GCSE/IGCSE Level) Instrumental Methods of Chemical Analysis Chromatography - Paper/Thin Layer Chromatography and Gas Chromatography GCSE/IGCSE Revision QUIZ on chemical tests for identifying ions, gases and compounds Part 1 contd. Alphabetical TEST INDEX for cations, anions, organic functional groups etc. Full list of KEYWORDS
for inorganic/organic
identification methods in alphabetical order
e.g. test/reagent for: * acid ==> H+ *
acid/acyl
chloride RCOCl * alcohols – general ROH/prim
RCH2OH/sec R2CHOH/tert
R3COH) * aldehyde RCHO
* prim aliphatic amine R–NH2 *
aliphatic/aromatic carboxylic acids * alkali
==> OH–
* alkane/alkene >C=C</alkyne –C Use the alphabetical test list above for identifying anions, cations, gases, molecules etc. to find what you require! for your KS3–KS4 Science–GCSE–IGCSE– Chemistry and GCE–AS–A2–IB–US grades 9–12 K12 advanced subsidiary chemistry course etc. and help you to identify unknown inorganic and organic compounds–molecules for qualitative analysis. Its also a good idea to read the brief notes after the alphabetical list. EMAIL query? comment? test missing? * Gas Preparations * Hazard warning signs/symbols–examples of labelling
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HAZARD
WARNING SYMBOLS (signs or labels)
A brief description of what the hazard might be. |
NEW SECTION currently working on the table of examples below. |
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WARNING | For all experiments, appropriate risk assessments should be done and hazcards studied etc. This section just illustrates the use of hazard warning signs with common examples, and may NOT provide sufficient detail for specific experiments, concentrations, coursework write up etc., but Google can! | ||||||
Symbol | Examples of what might be labelled/classified with this hazard warning sign (definitions above) | ||||||
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Irritant: Most acidic and alkaline solutions unless very dilute, VERY small quantities of acidic gases like chlorine, sulfur dioxide, nitrogen dioxide, very dilute bleaches. These may not be that corrosive BUT they are irritating e.g. will cause irritation of the skin and reddening and blistering. | ||||||
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Harmful - poisonous but not toxic: Some acids e.g. nitric acid; acidic gases like chlorine, sulphur dioxide, nitrogen dioxide; bleaches; heavy metal ions e.g. of lead, barium and copper (e.g. as copper sulfate) some salts e.g. silver nitrate, | ||||||
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Corrosive: Any substance like concentrated acidic or alkaline solutions which will attack many materials and destroy living tissue too! Also includes substances like bromine. | ||||||
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Highly flammable: Most organic solvents like hexane, propanone (acetone), petrol and other hydrocarbon fuels are easily ignited, easily catch fire. | ||||||
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Toxic: Chlorine, sulfur dioxide, hydrogen cyanide can cause death if breathed in with sufficient quantity, absorbed through the skin or ingested by swallowing. Salts of hydrogen cyanide e.g. potassium cyanide are highly toxic – you only have a short time to take an antidote mixture! | ||||||
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Oxidising: Chemicals that can act as oxidising agents e.g. chlorine gas/solution and oxygen gas/liquid, potassium manganate(VII), potassium chlorate (in some weed killers). Many oxidising agents donate oxygen to materials that burn and can be dangerously reactive. Many can cause combustion if mixed with an oxidisable combustible material. They may cause materials to burn more fiercely. | ||||||
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Radioactive: Radioisotopes giving off dangerous ionising radiation | ||||||
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Explosive: TNT, hydrogen, fireworks, peroxides | ||||||
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Biohazard: organisms and viruses infectious to humans, animals or plants (e.g. parasites, viruses, bacteria, fungi); and biologically active agents (i.e. toxins, allergens, venoms) | ||||||
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Harmful to the environment. e.g. chemicals toxic to aquatic wildlife an in general harmful to organisms and the environment e.g. toxic metals like mercury, old pesticides like DDT. |
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Carcinogenic: nitrates, organic aromatic compounds like phenols, | |||||||
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Doc Brown's Chemistry |
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