Experiment 14
Purpose : To determine the cation and anion of an inorganic substance.
Materials : KA 1 , KA 2 , dilute hydrochloric acid, distilled water, aqueous sodium
hydroxide, aqueous ammonia, aqueous ammonium chloride, aqueous
iron(III) chloride, aqueous silver nitrate, dilute nitric acid, aqueous
disodium hydrogen phosphate, aqueous potassium chromate(VI).
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) Solids KA 1 and KA 2 are simple salts. The following experiments
are carried out with solid KA 1 to identify its cation and anion.
(b) You are then required to plan and carry out a few experiments to
identify the cation and 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 KA 1
and 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) Add dilute hydrochloric acid to a small amount of solid KA 1 , then warm gently. | - White precipitate formed. | - Mg²+, Ca²+, Ba²+ may present. |
(d) Dissolve solid KA 1 in distilled water and filter. Use separate portions of the filtrate for tests (i) to (vi). (i) Add aqueous sodium hydroxide the in excess. | - White precipitate formed. - The white precipitate still remain when aqueous sodium hydroxide add in excess. | - Mg²+, Ca²+, Ba²+ may present. |
(ii) Add aqueous ammonia, then in excess followed by aqueous ammonium chloride. | - No changes. | - No deduction. |
(iii) Add aqueous iron(III) chloride, then warm. | - No changes. | - No deduction. |
(iv) Add aqueous silver nitrate, followed by dilute nitric acid. | - White precipitate formed. | - CI־, BrO3־, IO3־ may present. |
(v) Add aqueous disodium hydrogen phosphate. | - White precipitate formed. | - Ba²+ present. |
(vi) Add aqueous potassium chromate(VI) followed by dilute hydrochloric acid. | - Yellow precipitate formed. - When dilute hydrochloric acid added, the colour change to orange. | - Cl־ present. |
Identify of KA 1 : BaCl2
Test on KA 2 :
Test | Observation | Deduction |
(c) Add dilute hydrochloric acid to a small amount of solid KA 2 , then warm gently. | - Yellow precipitate formed with dilute hydrochloric acid. - Yellow precipitate yield when warm. - Gas released and change the blue litmus paper to red. | - The gas released is acidic. - S2O3²־ may present. |
(d) Dissolve solid KA 2 in distilled water and filter. Use separate portions of the filtrate for tests (i) to (vi). (i) Add aqueous sodium hydroxide the in excess. | - White precipitate formed with aqueous sodium hydroxide. - The white precipitate still remain when aqueous sodium hydroxide add in excess. | - Mg²+, Ca²+, Ba²+ may present. |
(ii) Add aqueous ammonia, then in excess followed by aqueous ammonium chloride. | - White precipitate formed with aqueous ammonia. - Remain constant when aqueous ammonia add in excess. - Dissolve in aqueous ammonium chloride. | - Mg²+ may present. |
(iii) Add aqueous iron(III) chloride, then warm. | - Colour of iron(III) chloride change from purple to colourness. - White precipitate formed when heat. | - S2O3²־ may present. |
(iv) Add aqueous silver nitrate, followed by dilute nitric acid. | - White precipitate formed when silver nitrate is added. - Colour immediately change from brown to black when dilute nitric acid added. | - S2O3²־ may present. |
(v) Add aqueous disodium hydrogen phosphate. | - White precipitate yield. | - Mg²+ may present. |
(vi) Add aqueous potassium chromate(VI) followed by dilute hydrochloric acid. | - Colour change from yellow to brown when dilute hydrochloric acid added. | - CrO4²־ change to CrO7²־ . |
Identify of KA 2 : MgS2O3
Conclusion : - Cation of KA 1 is Ba²+ and the anion of KA 1 is Cl־ .
- Cation of KA 2 is Mg²+ and the anion of KA 2 is S2O3²־ .
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.
1 comment:
Daebak..very useful
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