RP4 - Testing for Cations and Anions Flashcards
Describe the test for group 2 metal ions and transition metals (hydroxides)
Place 10 drops of the metal ion solution in a test tube.
Add 10 drops of sodium hydroxide solution and mix well.
Continue to add sodium hydroxide solution dropwise with gentle shaking, until in excess
What happens to group 2 hydroxides down the group
Become more soluble down the group
Results of the test for group 2 metal ions
Mg2+ forms white precipitate
Ca2+ forms white precipitate
Sr2+ and Ba2+ do not form hydroxide precipitate
Result of addition of NaOH (in excess after) with Al 3+
Forms a white precipitate which dissolves in excess sodium hydroxide to form a colourless solution.
Results for transition metals when NaOH added until in excess
Copper solutions form blue ppt
Fe2+ solutions form green ppt
Fe3+ solutions form brown ppt
Test form ammonium ions (NH4+)
Place 10 drops ammonium chloride in a test tube
Add 10 drops of NaOH solution and shake
Warm the mixture in test tube gently with a water bath
(Alkaline ammonia gas is released)
Test fumes released from mixture by holding a piece of damp red litmus paper in mouth of test tube.
Red litmus goes blue
Test for group 2 metal ions (sulfates)
Add 10 drops of the metal ion to a test tube.
Add 10 drops of sulfuric acid
Continue to add sulfuric acid solution, dropwise with gentle shaking, until in excess
What happens to group 2 sulfates down the group
Becomes less soluble
Results of testing for group 2 metal ions with a sulfate
Mg2+ and Ca2+ do not form a sulfate precipitate
Sr and Ba 2+ form white precipitates
Describe the test for sulfate ions
Add acidified (with HCl to remove carbonate impurities) barium chloride to a solution.
White precipitate forms.
Describe the test for halide ions.
Add nitric acid and silver nitrate solution.
Chloride produces white precipitate
Bromide produces cream precipitate
Iodide produces yellow precipitate
Add ammonia solution to help differentiate if colours look similar
Describe the test for carbonate ions
Add dilute HCl and there will be effervescence.
Bubble the gas through limewater and limewater goes cloudy.
Test for hydroxide ions
Turn red litmus blue
Observation in reaction of chloride salts with conc H2SO4
White steamy fumes of HCl
Observation in reaction of fluoride salts with conc H2SO4
White steamy fumes of HF
Observation in reaction of bromide salts with conc H2SO4
Orange fumes of bromine formed
Colourless acid gas, SO2 formed
Observations in reaction of iodide salts with conc H2SO4
Black solid and purple fumes of iodine formed
Colourless acidic gas, SO2 produced
yellow solid of sulfur
bad smell of H2S
