qualitative analysis Flashcards
What are anions
Negative ions
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
How can you test for sulfate ions, SO4 2-
- Add dilute HCL and barium chloride to the sample
What are the observations for a positive test of sulfate ions, SO4 2-
- White precipitate of barium sulphate
What do you use to test for halide ions
Acidified AgNO3
Why do you add HNO3 to test for halide ions and why not HCl
- To remove CO3 2-
- Adding HCl would add Cl- ions, giving a false positive result
How can you test for a halide ion
- Dissolve sample in water
- Add aqueous silver nitrate
- Record colour change
- If difficult to distinguish the colour, add aqueous ammonia
- Note the solubility of the precipitate
What are the results of a positive chloride ion test
The white precipitate, soluble in dilute aqueous ammonia
What are the results of a positive bromide ion test
Cream precipitate, soluble in concentrated ammonia only
What are the results of a positive iodide ion test
Yellow precipitate, insoluble in concentrated and dilute aqueous ammonia
When testing for carbonate, sulphate and halide ions, in which order should the tests be carried out and why
- Carbonate
- Sulfate
- Halide
- Barium sulfate and barium carbonate are insoluble
- Sulfate ions will produce a precipitate in silver nitrate
What are cations
Positive ions
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
- Red litmus paper turns blue
- Ammonia has a pungent smell
