Flashcards QA - Test for anions
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13 Terms
test for CO₃²⁻
Add dilute nitric acid, HNO₃(aq)
Observation for test of CO₃²⁻
Effervescence observed
Colourless and odourless gas evolved forms white precipitate with limewater
Gas is carbon dioxide (CO₂)
Test for SO₄²⁻
Acidify with dilute nitric acid, HNO₃(aq), then add aqueous barium nitrate, Ba(NO₃)₂(aq)
Observation for test of SO₄²⁻
White precipitate is formed
Test for Cl⁻
Acidify with dilute nitric acid, HNO₃(aq), then add aqueous silver nitrate, AgNO₃(aq)
Observation for test of Cl⁻
White precipitate is formed
Test for I⁻
Acidify with dilute nitric acid, HNO₃⁻(aq), then add aqueous silver nitrate, AgNO₃(aq)
Lead nitrate, Pb(NO₃)₂(aq) can also be used based on solubility table
Observation for test of I⁻
yellow precipitate is formed
Test for NO₃⁻
Add aqueous sodium hydroxide, NaOH(aq), then add aluminium foil, warm carefully
Observation for test of NO₃⁻
Colourless, pungent gas evolved which turned damp red litmus paper blue.
Gas is ammonia (NH₃)
In an unknown solution, aqueous sodium hydroxide is added, followed by aluminium foil. It was then warmed carefully. A colourless and pungent gas evolved which turned damp red litmus paper blue. What ions can the unknown solution contain?
ammonium ion and nitrate ion
What do you think is the purpose of adding dilute acids in the test for barium sulfate?
As barium carbonate is a white precipitate, hence the addition of acid will react with and remove any carbonate ions. Therefore, any white precipitate that forms can be correctly identified as barium sulfate.
What do you think is the purpose of adding dilute acids in the test for silver nitrate to identify chlorides and iodides?
As silver carbonate is a light-yellow precipitate while silver hydroxide is a brown precipitate. Hence, the addition of acid will react with and remove any carbonate ions or hydroxide ions. Therefore, any precipitate that forms following the addition of silver nitrate can be correctly identified (i.e. AgCl (white precipitate) and AgI (yellow precipitate)).