Tests Flashcards
Test for ammonium ions?
Add NaOH to the sample
Warm the solution
Place damp red litmus paper near the mouth of the test tube
If ammonium ions are present, the indicator paper will turn blue
Why does the test for cations work?
NaOH= stronger base than NH4
Warming the solution- Causes more gas to be given off more quickly
To test for alkali- red litmus paper has to be damp in order to dissolve ammonia
Formula for ammonium ions and hydroxide ions?
NH4+ + OH- -> NH3 + H2O
Order of tests for anions?
Carbonate, sulphate, halides
Why does carbonate test come first?
Most carbonates are insoluble
Test for carbonate ions?
1) add dilute nitric acid to the sample
2) if bubbles form- could be carbonate
3) test the gas by bubbling through limewater
4) if carbonate ions are present, limewater turns cloudy
Why does the test for sulphate ions come second?
Ag2SO4 is insoluble
Process for sulphate ions?
1) add dilute nitric acid to the sample to remove carbonate ions
2) add barium chloride
3) if sulphate ions are present, a white precipitate forms
Why does halide test come last?
You will get false results if carbonate/sulphate ions aren’t identified first
Process for halide ions?
1) add dilute nitric acid to the sample to remove carbonate ions
2) add silver nitrate
3) if halide ions are present, you will see a precipitate
Colour of the Cl-, BR- and I- precipitates?
Cl= white
Br= cream
I= yellow
Is the Cl- ion ppt soluble in dilute and concentrated NH3?
Yes
Is the Br- ion ppt soluble in dilute and conc NH3/
Only soluble in conc NH3
Is the I- ion ppt soluble in conc and dilute NH3?
Not soluble in NH3
