It swells up into a fluffy white porous mass which then melts into a colourless liquid that later forms a clear transparent glassy bead consisting of boric anhydride and sodium metaborate.īoric anhydride is non-volatile. (e) Borax Bead Testīorax, Na 2B 4O 7.10H 2O, on heating gets fused and loses water of crystallisation. For proceeding to this test, the paste of the mixture with conc.HCl is introduced into the flame using a platinum wire. This colour can give reliable information of the presence of certain cations. Their vapours impart characteristic colour to the flame. HCl forms their chloride, that are volatile in non-luminous flame. (d) Flame TestĬertain salts on reacting with conc. In addition to metallic oxides, phosphates and borates also react with cobalt oxide to form Co 3(PO 4 )2 and Co 3(BO 3) 2 that are blue in colour. This on treatment with cobalt nitrate and on subsequent heating forms a double salt of the formula MgO.CoO, which is pink in colour. This combines with the metallic-oxides present as white residue in the charcoal cavity forming coloured compounds.įor example, when a magnesium salt undergoes charcoal cavity test, a while residue of MgO is left behind. The test is based on the fact that cobalt nitrate decomposes on heating to give cobalt oxide, CoO. This test is based on the fact that metallic carbonates when heated in a charcoal cavity decomposes to give corresponding oxides. This test is applied to those salts that leave white residue in the charcoal cavity test. In certain cases, the oxides formed partially undergo reduction to the metallic state producing metallic beads or scales. The oxides appear as coloured incrustation or residue in the cavity. Characteristic smell helps to identify some ions like ammonium ion. The test is not much reliable, but certainly helpful in identifying some coloured cations. The physical examination of the unknown salt involves the study of colour, smell and density. (a) Physical Appearance: Colour and Smell Some preliminary tests needs to be done before doing the analysis of cations. Qualitative Analysis of Cations Preliminary Tests Let us discuss about the Qualitative Analysis of Cations. There are separate procedures for detecting cations and anions, called the Cation Analysis and Anion Analysis. Testing with various reagents gives characteristic reaction of certain ions, which may be a colour change, a solid formation or any other visible changes. The common procedure for testing any unknown sample is to make its solution and test this solution with various reagents for the ions present in it.
It is mainly concerned with the detection of ions in an aqueous solution of the salt. Qualitative analysis is a method of Analytical chemistry that deals with the determination of elemental composition of inorganic salts. Our objective is to determine the cation present in a given salt.
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