In the qualitative analysis of an inorganic substance number of tests are carried out in order to discover the acidic and basic radical present in it. A test is an experiment along with an observation made to show the presence or absence of a certain substance or class of substances. In the test we note the formation or disappearance of
(I) a colour or (ii) a precipitate or (iii)a gas (iv) an odour The test may be positive or negative. A positive test is one that gives the result indicated in the procedure and shows the presence of the particular radical. A negative test is one which does not give the indicated results and shows the absence of the particular radical. The substances or solutions added to bring about the reactions are called reagents. http://www.tndte.com/TEXT%20BOOKS/Book-Unit%20wise/Engineering%20Chemistry-I%20&%20II/Chem_First%20Sem-II%20-%20Practical.pdf
Topic : Qualitative analysis.
Purpose : To determine the cations and anions in a mixture of inorganic salts.
Theory : Cations and anions of unknown inorganic substances can be determined
through qualitative analysis.
Materials : KA 1 and KA 2 solutions, distilled water, aqueous sodium
hydroxide, aqueous potassium iodide, aqueous potassium chromate(VI),
aqueous sodium ethanoate, aqueous sodium carbonate, dilute sulphuric
acid, iron(II) sulphate, concentrated sulphuric acid, dilute nitric acid,
lead(II) nitrate solution, Alloy Devordas.
Apparatus : One test tube rack with six test tubes.
One hard glass test tube with delivery tube.
One test tube holder.
One filter funnel and two piece of filter papers.
One feat pipette.
One Bunsen burner.
Red and blue litmus paper.
One wash bottle filled with distilled water.
Procedure : (a) KA 1 and KA 2 are mixtures of two salts. The following
experiments are carried out with solid KA 1 to identify its cation.
(b) You are then required to plan and carry out a few experiments to
identify the anion present in solid KA 2 .
In all the experiments, the reagent should be added gradually until no
further change is observed. Observations and deductions made from them
are recorded in the spaces provided. Deduce what you can about cations in
KA 1 and anions in KA 2 . Details of colour changes, precipitates, and
tests on gases evolved should be included in the observations, and the
stage in a test at which a change occurs should be indicated clearly.
Test on KA 1 :
Test| Observation| Deduction|
(c) Dissolve all of the solid KA 1 in distilled water and filter. Use separate portions of the filtrate for tests (i) to (v). (i) Add aqueous sodium hydroxide, then in excess, and warm.| - White precipitate formed at first, then change to colourless when in excess.- The litmus paper changes from red to blue when warm it.| - Al³+, NH4+, Zn²+, Pb²+ may present.| (ii) Add aqueous potassium iodide.| - No changes, remain still.| - Al³+, Ba²+, Ca²+, Zn²+, Mg²+may present.| (iii) Add aqueous potassium chromate(VI).| - Colour of solution...