Revision notes: Revision of qualitative chemical tests
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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
QUALITATIVE CHEMICAL TEST INDEX
Part 1 Introduction to chemical testing and analysing substances (this page)
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.
(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)
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 –CC– (saturated versus unsaturated) * aluminium/aluminum ion Al3+ * amide RCONH2 * prim aliphatic amines R–NH2 * ammonia gas NH3 * ammonium ion NH4+ * prim aromatic amine C6H5–NH2 etc. * barium ion Ba2+ * Benedict's solution * Brady's reagent * bromide ion Br– * bromine Br2 * caesium ion Cs+ * calcium ion Ca2+ by flame or hydroxide ppt. * carbonate CO32–/hydrogencarbonate HCO3– with acid or effect of heating metal carbonate e.g. MCO3 * carbon dioxide gas CO2 * carboxylic acid RCOOH * carboxylic acid (aliphatic) salts e.g. RCOO–Na+ * chloride ion Cl– * chlorine gas Cl2 * Chromate(VI) ion CrO42– * copper(II) ion Cu2+ by flame or hydroxide ppt. * 24DNPH (for aldehydes/ketones test) * esters RCOOR * Fehlings test/solution * flame test for metal ions * fluoride ion F– * haloalkanes/halogenoalkanes R–X * hydrogen gas H2 * hydrogen sulphide H2S * hydrogen ion, acids H+ * hydrogen bromide gas/hydrobromic acid HBr * hydrogen chloride gas/hydrochloric acid HCl * hydrogen iodide gas/hydriodic acid HI * hydroxide ion, alkali OH– * hydroxy/alcohol/phenol (organic) * iodide ion I– * iodine I2 * iodoform test – formation of CHI3 * iron(II) ion Fe2+ * iron(III) ion Fe3+ * ketone R2C=O * lead(II) ion Pb2+ * lithium ion Li+ * lime water Ca(OH)2(aq) * magnesium ion Mg2+ * metal carbonates–heating e.g. MCO3 * metal ions via hydroxide precipitate * nitrate or nitrate(V) NO3– * nitrite or nitrate(III) NO2– * nitrogen dioxide or nitrogen(IV) oxide NO2 * oxygen gas O2 * phenols C6H5OH etc. * potassium ion K+ * rubidium ion Rb+ * reducing sugars * saturated/unsaturated * silver nitrate AgNO3 (see chloride, bromide, iodide tests) * sugars (reducing) * sodium ion Na+ * strontium Sr+ * 'sulphate/sulfate' or sulphate(VI) SO42– * sulphide S2– * 'sulphite/sulfite' or sulphate(IV) SO32– * sulphur dioxide gas SO2 * Tollen's Reagent * unsaturated/saturated * water H2O * zinc ion Zn2+ *
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.
WARNING SYMBOLS (signs or labels)
A brief description of what the hazard might be.
Biohazard: Biohazardous materials include anything that may cause disease in living organisms or cause significant impact to the environment or community.
NEW SECTION currently working on the table of examples below.
|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)|
|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.|
|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,|
|Corrosive: Any substance like concentrated acidic or alkaline solutions which will attack many materials and destroy living tissue too! Also includes substances like bromine.|
||Highly flammable: Most organic solvents like hexane, propanone (acetone), petrol and other hydrocarbon fuels are easily ignited, easily catch fire.|
|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!|
|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.|
|Radioactive: Radioisotopes giving off dangerous ionising radiation|
|Explosive: TNT, hydrogen, fireworks, peroxides|
|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)|
|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.
|Carcinogenic: nitrates, organic aromatic compounds like phenols,|
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