Qualitative Analysis Flashcards
How can you test for carbonate ions.
CO3 2-
Add strong acid to the sample
Collect the gas produced
Pass through lime water
What are the observations for a positive test of carbonate ions, CO3 2- ?
Fizzing
Limewater turns cloudy
CO3 2- + 2 H+ —> H2O + CO2
How can you test for Sulphate ions, SO4 2- ?
Add dilute hydrochloric acid and barium chloride to the sample
What are the observations for a positive tests for sulfate ions SO4 2-?
White precipitate of barium sulfate is produced
Write an equation for the sulfate ion test
Ba2+ + SO4 2- —> BaSO4 (s)
What do you use to test for halide ions?
Acidified AgNo3
Why do you add HNO3 to test for halides ions and why not HCL ?
To remove carbonate
Adding HCL would add Cl- ions giving a false positive result
How can you test for a halide ion?
Dissolve the sample in water Add aqueous silver nitrate Record the colour change If difficult to distinguish the colour, add aqueous ammonia, first dilute ammonia then concentrated ammonia Note solubility or precipitate
Write the result and equation for Cl- ions?
White precipitate, soluble in dilute aqueous ammonia
Write the result and equation for Br- test
Cream ppt. Soluble in concentrated aqueous ammonia only
Write the result and equation for I- test
Yellow ppt
Insoluble in concentrated and dilute aqueous ammonia
When testing for carbonate, sulfate, halide ions in which order should the tests be carried out and why?
- Carbonate tests
- Sulfate test
- Halide test
Because Barium ions forms an insoluble precipitate of BaCO3 and silver ions form insoluble precipitate Ag2SO4
How can you test for ammonium ions, NH4 + ?
Add sodium hydroxide to the sample and warm it
Test the gas produced with red litmus paper
What are the observations for positive ammonium ions test?
Red litmus paper turns blue
Ammonia has a pungent smell
Write the equation for ammonium ions test
NH4 + + OH- —> NH3 + H2O
