RP4 : Testing for anions - Group 7 ions , OH- , CO32- , SO42- Flashcards
What is used as a reagent to test for sulphate ions
BaCl2 solution acidified with HCl
what’s the result of a solution containing sulfate ions when acidified BaCl2 is added
a white ppt of barium sulfate is formed
Ionic equation :
Ba2+(aq) + SO42-(aq) => BaSO4(s)
what’s the result of other anions not containing sulfate ions reacting with acidified BaCl2
Other anions should give a negative result which is no precipitate forming
how can you test for presence of halide ions
- add nitric acid
- add silver nitrate solution dropwise
what’s the role of adding nitric acid when testing for halides
To react with any carbonates present to prevent formation of the precipitate Ag2CO2 . This would mask the desired observations
2HNO3 + Na2CO3 => 2NaNO3 + H2O + CO2
what’s the result of adding silver nitrate solution to halides
fluorides produce no ppt
•Chlorides produce a white ppt
Ag+ (aq) + Cl- (aq) => AgCl(s)
• Bromides produce a cream ppt
Ag+ (aq) + Br-(aq) => AgBr(s)
Iodides produce a pale yellow ppt
Ag + (aq) + I-(aq) => AgI(s)
what’s the observations of adding ammonia solution to help differentiate between the halide ions
Silver chloride dissolves in dilute ammonia to form a complex colourless ion
- AgCl(s) + 2NH3(aq) => [Ag(NH3)2]+(aq) + Cl- (aq)
Silver bromide dissolves in concentrated ammonia to form a complex ion colourless
AgBr(s) + 2NH3(aq) => [Ag(NH3)2]+ (aq) + Br-(aq)
Silver iodide does not react with ammonia it’s too insoluble
what’s the test for presence of carbonate ions
Add any dilute acid and observe effervescence
Bubble gas through limewater to test for CO2 - will turn limewater cloudy
Fizzing due to CO2 would be observed if a carbonate was present
2HCl + Na2CO3 => 2NaCl + H2O + CO2
How do you test for presence of hydroxide ions
Alkaline hydroxide ions will turn red litmus paper blue
