Qualitative analysis (Tests for cations using aqueous NaOH)
**Take note that qualitative analysis is a very useful and important technique used by chemists to find out the identity of an aqueous substance by testing for the type of cation and anion found in the aqueous solution of the substance.
Copper (II) cation = blue ppt. (ppt. does not dissolve in excess NaOH)
Iron (II) cation = green ppt. (ppt. does not dissolve in excess NaOH)
Iron (III) cation = brown ppt. (ppt. does not dissolve in excess NaOH)
Calcium cation = white ppt. (ppt. does not dissolve in excess NaOH)
Aluminium cation = white ppt. (ppt. dissolves in excess NaOH)
Zinc cation = white ppt. (ppt. dissolves in excess NaOH)
Lead cation = white ppt. (ppt. dissolves in excess NaOH)
Ammonium cation = no ppt. Ammonia gas produced.
See following video on test for copper (II) cation
Copper (II) cation = blue ppt. (ppt. does not dissolve in excess NaOH)
Iron (II) cation = green ppt. (ppt. does not dissolve in excess NaOH)
Iron (III) cation = brown ppt. (ppt. does not dissolve in excess NaOH)
Calcium cation = white ppt. (ppt. does not dissolve in excess NaOH)
Aluminium cation = white ppt. (ppt. dissolves in excess NaOH)
Zinc cation = white ppt. (ppt. dissolves in excess NaOH)
Lead cation = white ppt. (ppt. dissolves in excess NaOH)
Ammonium cation = no ppt. Ammonia gas produced.
See following video on test for copper (II) cation
Qualitative analysis (Test for cations using aqueous ammonia)
Copper (II) cation = blue ppt. (ppt. dissolves in excess aqueous ammonia forming dark blue solution)
Iron (II) cation = same result as test using aqueous NaOH
Iron (III) cation = same result as test using aqueous NaOH
Calcium cation = No ppt. formed
Aluminium cation = white ppt. (ppt. does not dissolve in excess aqueous ammonia)
Zinc cation = same result as test using aqueous NaOH
Lead cation = white ppt. (ppt. does not dissolve in excess aqueous ammonia)
Ammonium cation = No ppt. formed. No ammonia gas produced.
(*Take note that zinc cation can be distinguished from aluminium and lead cation by adding aqueous ammonia as all three cations produced white ppt. Only zinc cation dissolves in excess aqueous ammonia)
(*Take note that lead cation can be further distinguished from aluminium cation by adding aqueous potassium iodide. If lead cation is present, ayellow ppt. of lead (II) iodide is formed.
Iron (II) cation = same result as test using aqueous NaOH
Iron (III) cation = same result as test using aqueous NaOH
Calcium cation = No ppt. formed
Aluminium cation = white ppt. (ppt. does not dissolve in excess aqueous ammonia)
Zinc cation = same result as test using aqueous NaOH
Lead cation = white ppt. (ppt. does not dissolve in excess aqueous ammonia)
Ammonium cation = No ppt. formed. No ammonia gas produced.
(*Take note that zinc cation can be distinguished from aluminium and lead cation by adding aqueous ammonia as all three cations produced white ppt. Only zinc cation dissolves in excess aqueous ammonia)
(*Take note that lead cation can be further distinguished from aluminium cation by adding aqueous potassium iodide. If lead cation is present, ayellow ppt. of lead (II) iodide is formed.
Qualitative analysis (Tests for anions)
Carbonate: Add dilute acid (e.g. HCl).
Test result: Bubbles of carbon dioxide gas produced which forms a white ppt. with limewater (CaOH).
**Take note this is a typical reaction of acid and a carbonate to produce carbon dioxide gas as one of the products.
See following video for the test for carbonate ion (solid calcium carbonate is the sample tested for presence of carbonate ion)
Test result: Bubbles of carbon dioxide gas produced which forms a white ppt. with limewater (CaOH).
**Take note this is a typical reaction of acid and a carbonate to produce carbon dioxide gas as one of the products.
See following video for the test for carbonate ion (solid calcium carbonate is the sample tested for presence of carbonate ion)
Chloride: Acidify with nitric acid and then add aqueous silver nitrate.
Test result: White ppt. of silver chloride formed.
Explanation: Silver ions have reacted with chloride ions to form insoluble silver chloride.
See following video on test for chloride ion
Test result: White ppt. of silver chloride formed.
Explanation: Silver ions have reacted with chloride ions to form insoluble silver chloride.
See following video on test for chloride ion
Iodide: Acidify with nitric acid and then add aqueous lead (II) nitrate.
Test result: Yellow ppt. of lead (II) iodide formed.
Explanation: Lead ions have reacted with iodide ions to form insoluble lead (II) iodide.
See following video on test for iodide ion.
Test result: Yellow ppt. of lead (II) iodide formed.
Explanation: Lead ions have reacted with iodide ions to form insoluble lead (II) iodide.
See following video on test for iodide ion.
Sulphate: Acidify with nitric acid and then add aqueous barium nitrate.
Test result: White ppt. of barium sulphate formed.
Explanation: Barium ions have reacted with sulphate ions to form barium sulphate.
See following video on test for sulphate ion.
Test result: White ppt. of barium sulphate formed.
Explanation: Barium ions have reacted with sulphate ions to form barium sulphate.
See following video on test for sulphate ion.
Nitrate: Add aqueous sodium hydroxide, and then add aluminium foil and warm mixture.
Test result: Ammonia gas is produced and the gas turns damp red litmus paper blue.
See following video on test for nitrate ion.
Test result: Ammonia gas is produced and the gas turns damp red litmus paper blue.
See following video on test for nitrate ion.
Tests for gases
Ammonia: Test the gas with damp red litmus paper.
Test result: Damp red litmus paper turns blue.
**See the video just before this where the test result for ammonia gas is towards the end of video.
Carbon dioxide: Pass the gas into limewater (aqueous calcium hydroxide).
Test result: White ppt. forms in limewater.
**See the video on test for carbonate ion where the test result for carbon dioxide gas is towards end of video.
Chlorine: Test gas with damp blue litmus paper.
Test result: Litmus paper becomes bleached.
See following video on test for chlorine gas.
Test result: Damp red litmus paper turns blue.
**See the video just before this where the test result for ammonia gas is towards the end of video.
Carbon dioxide: Pass the gas into limewater (aqueous calcium hydroxide).
Test result: White ppt. forms in limewater.
**See the video on test for carbonate ion where the test result for carbon dioxide gas is towards end of video.
Chlorine: Test gas with damp blue litmus paper.
Test result: Litmus paper becomes bleached.
See following video on test for chlorine gas.
Hydrogen: Test gas with lighted wooden splint.
Test result: Gas burns with a 'pop' sound.
See following video on test for hydrogen gas.
Test result: Gas burns with a 'pop' sound.
See following video on test for hydrogen gas.
Oxygen: Put glowing wooden splint into gas.
Test result: Glowing splint relights.
See following video on test for oxygen gas.
Test result: Glowing splint relights.
See following video on test for oxygen gas.
Sulphur dioxide: Put a drop of acidified potassium dichromate (VI) on a paper strip and apply it to gas.
Test result: Orange colour of acidified potassium dichromate (VI) turns green.
See following video on test for sulphur dioxide (*Note that the video did not use paper strip but instead introduce sulphur dioxide into potassium dichromate (VI) directly which is another possible way).
Test result: Orange colour of acidified potassium dichromate (VI) turns green.
See following video on test for sulphur dioxide (*Note that the video did not use paper strip but instead introduce sulphur dioxide into potassium dichromate (VI) directly which is another possible way).