CHEM- Describing Tests for Cations
Chemistry, Chemical Tests, Cations- IBDP | DSE | GCE | IAL | AP Chemistry
Chemical tests help identify the presence of different cations.🤓
Take a look at this example🙃
Part I: Flame Test
Procedure: First, dip a clean nichrome wire into concentrated hydrochloric acid. Then, dip the nichrome wire into each of the cations. Finally, put the end of the wire in the Bunsen flame and observe the color of the flame.
Li+ : Deep Red
Ni+ : Golden-yellow
K+ : Lilac
NH+(aq) + OH- (aq) →NH3 (g) + H2O (l)
A solution containing NH+ does not give any precipitate with sodium hydroxide.
Instead, a solution containing NH+ gives off ammonia gas when warmed with sodium hydroxide.
NH3 (g) turns moist red litmus paper blue
Procedure: Prepare solutions containing Cu 2+ , , Fe2+ and Fe3+ ions and add sodium hydroxide to each of the sample solutions. The cations can be distinguished based on the observations
1) Cu2+ (aq) + 2OH- (aq) →Cu(OH)2 (s)
🧐Formation of a pale blue precipitate
2) Fe2+ (aq) + 2OH- (aq) → Fe(OH)2 (s)
🧐Formation of a green precipitate.
The green Fe(OH)2 turns brown on prolonged standing in air due to the formation of Iron (III) hydroxide :
4Fe(OH)2 (s) + 2H2O (l) + O2 (g) → 4Fe(OH)3 (s)
3)Fe3+ (aq) + 3OH- (aq) →Fe(OH)3 (s)
🧐Formation of a reddish brown precipitate
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