Tests for ions Flashcards
How do you carry out a flame test?
Dip a nichrome wire loop in concentrated hydrochloride acid and then dip it into the unknown compound
What colour will the flame for Ca2+ be?
Brick red
What is a flame test used for?
To identify positive ions of group 2 elements
What colour will the flame for Sr2+ be?
Red
What colour will the flame for Ba2+ be?
pale green
What can you use to test for ammonium ions? Why is this possible?
Red litmus paper
It is an alkaline
What colour change will occur with litmus paper if ammonium ions are present?
Red to blue
What reaction can you use to test whether a substance contains ammonium ions?
Add dilute hydroxide solution to the mystery sample
If ammonia gas is given off and there is a colour change with the red litmus paper then there must be ammonium ions present in the sample
What is the equation for the reaction of hydroxide solution with a solution containing ammonium ions?
NH4+(aq) + OH- (aq) -> NH3 (g) + H2O (l)
How do you test for a negative sulphate ion?
Add dilute hydrochloric acid followed by barium chloride solution (BaCl2).
If a white precipitate of barium sulphate forms, the original compound contained a sulphate
What is the ionic equation for the reaction between a sulfate ion and barium chloride?
Ba 2+ (aq) + SO4 2- (aq) -> BaSO4(s)
What do hydroxide solutions do to solutions?
Turn them alkaline
What can be used to test if a solution has hydroxide ions?
A pH indicator test
Red litmus will turn blue
What test is used for halide ions?
Add dilute nitric acid (HNO3) followed by silver nitrate solution (AgNO3)
What result will chloride ions give if they are present?
They will form a white precipitate of silver chloride
What result will bromide ions give if they are present?
They will form a cream precipitate of silver bromide
What result will iodide ions give if they are present?
They will form a yellow precipitate of silver iodide
What will silver chloride dissolve in? (further test for confirmation)
Dilute ammonia solution
What will silver bromide dissolve in? (further test for confirmation)
Concentrated ammonia solution
What will silver iodide dissolve in? (further test for confirmation)
It wont dissolve in either ammonia solution
What test can be used for carbonate ions?
Add an acid
If present, fizzing will occur (effervescence)
What equation shows the reaction of carbonate ions with an acid?
CO3 2- (aq) + 2H+(aq) -> CO2 (g) + H2O(l)
How can you do further testing to make sure that the gas produced is actually CO2?
Bubble the gas through limewater and it will turn it cloudy if it is.
