Testing for ions
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How are halide ions tested for?
Adding AQUEOUS silver nitrate
What indicated the presence of the following ions when silver nitrate solution is added? i) chloride ii) bromide iii) iodide
i) white precipitate ii) cream precipitate iii) yellow precipitate
What can act as a further test to confirm which halide ion is present?
By adding dilute and concentrated AQUEOUS ammonia
What happens to silver chlorine in the presence of dilute ammonia?
It dissolves
What happens to silver chloride in the presence of concentrated ammonia?
It dissolves
What happens to silver bromide in the presence of dilute ammonia?
No visible change
What happens to silver bromide in the in the presence of concentrated ammonia?
It dissolves
What happens to silver iodide in the presence of dilute ammonia?
No visible change
What happens to silver iodide in the presence of concentrated ammonia?
No visible change
What happens to silver halides when they are exposed to light?
They decompose and release silver metal
State a use for the reaction that occurs when silver halides are exposed to light
It is used in chemical photography to create contrast on an image
What is the test for sulfate ions? How does this work?
Barium nitrate solution is added This reacts with the sulfate ions and forms an insoluble precipitate
What is seen when sulfate ions are present when barium nitrate solution is added?
A white precipitate is formed
i) What is used to test for carbonate ions? ii) What is observed if carbonate ions are present? iii) What can act as a further test to confirm this?
i) Dilute nitric acid is added ii) Effervescence occurs iii) The gas produced can be bubbled through limewater, if it is CO2 then a white precipitate will be formed in the limewater
Write the ionic equation for the sulfate ion test
SO4 2- (aq) + Ba2+ (aq) —-> BaSO4 (s)
i) What is the test for ammonium ions? ii) What is observed if ammonium ions are present?
i) Sodium hydroxide solution is added and the solution is placed in a hot water bath ii) A pungent smelling gas is given off which turns damp red litmus paper blue
Write an ionic equation for the reaction of ammonium sulfate solution with sodium hydroxide solution
NH4+ (aq) + OH- (aq) —> NH3 (g) + H2O (l)
Why does a positive test for ammonium ions turn damp red litmus paper blue?
Ammonia is produced which is an alkali gas
What is the best order for ion tests?
• Carbonate ions • Sulfate ions • Halide ions • Ammonium ions
What state must all the substances being tested for ions be?
They must be in AQUEOUS SOLUTION