Experiment 15
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.
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 changes to yellow. | - Al³+ present. |
(iv) Add aqueous sodium ethanoate, then warm. | - That is remain still. - When warm the solution, it will get white precipitate yield. - The colour of litmus paper change from blue to red. | - Al³+ present. |
(v) Add aqueous sodium carbonate, then warm. | - White precipitate yield at first then get red precipitate when warm it. | - Al³+, Ba²+, Ca²+, NH4+ may present. |
Identify of cations present in KA 1 : Al³+ and NH4+.
Test on KA 2 :
Test | Observation | Deduction |
(c) Dissolve all of the solid KA 2 in distilled water and filter. Use separate portions of the filtrate for tests (i) to (iii). (i) Add dilute sulphuric acid and iron(II) sulphate. Then, add a few drops of concentrated sulphuric acid in fume chamber. | - The solution remain still when dilute sulphuric acid is added. - Then, a brown ring is formed when a few drops of concentrated sulphuric acid is added in the fume chamber. | - NO3־ present. |
(ii) Add KA 2 with dilute nitric acid and lead(II) nitrate solution. Heat the mixture and let it cool down. | - Yellow precipitate yield at first. - Then, the yellow precipitate dissolved when warmed. - Yellow and shinning crystal formed when it cool down. | - I־ present. |
(iii) Add a few drops of sodium hydroxide and Alloy Devardas into KA 2 . Then heat it and test the gas produced with red litmus paper. | - Gas released when heated the solution. - The gas change the colour of litmus paper from red to blue. | - NO3־ present. |
- Anions of KA 2 are I־ and NO3־.
Comment : The results of qualitative analysis may be effected by :-
(i) The change of colour, occurred so fast and cannot be observed.
(ii) The amount of salt use too much may affect the results.
(iii) The gas liberated when being heating do not tested.
No comments:
Post a Comment