Simple Qualitative Analysis

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Simple qualitative analysis involves the identification of the constituents of an inorganic substance or a mixture of substances. The inorganic substances are split-up into two types of charged particles one of which is positively charged and the other is negatively charged. The charged particles are called ions or radicals. The positively charged ions are called cation or basic radical. The negatively charged ion is called anion or acid radical.

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.

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 spatula.

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.

Wooden splint.

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.

Results :        

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...
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