Group 7, the Halogens: Trends in Properties - Tests for Halides Flashcards
What reagent is used to test for halide ions?
- Acidified silver nitrate
What acid is used to acidify the silver nitrate?
- Nitric acid
Why does the solution need to be acidified before adding silver nitrate?
- To remove any impurities (carbonate and hydroxide ions)
- Would form AgOH and Ag2CO3 which would produce precipitates
- Resulting in a false positive
Why can’t you add hydrochloric acid instead of nitric acid?
- HCl would provide additional Cl- ions
- Could lead to a false positive
Give the general ionic symbol equation of the reaction between acidified silver nitrate and halides, including symbol equations
- Ag+ (aq) + X- (aq) → AgX (s)
What colour precipitate will Cl- ions produce when reacted with acidified silver nitrate?
- White precipitate
What colour precipitate will Br- ions produce when reacted with acidified silver nitrate?
- Cream precipitate
What colour precipitate will I- ions produce when reacted with acidified silver nitrate?
- Yellow precipitate
Which halide ion doesn’t produce a precipitate when reacted with acidified silver nitrate?
- F-
Why doesn’t F- produce a precipitate when reacted with acidified silver nitrate?
- AgF is soluble
What reagent is used to further distinguish between halide ions?
- Ammonia
- NH3
Why is there a further test to distinguish between the halide ions?
- Can be hard to tell the difference between the different colour precipitates
Describe the solubility of each silver halide in dilute ammonia
- AgCl (white precipitate) dissolves
- AgBr (cream precipitate) partially dissolves, no observable change
- AgI (yellow precipitate) insoluble, no observable change
Describe the solubility of each silver halide in concentrated ammonia
- AgCl (white precipitate) dissolves
- AgBr (cream precipitate) dissolves
- AgI (yellow precipitate) insoluble, no observable change
