Required practical 4 Flashcards
Describe the test for halide ions
- Add dilute HNO3 (to remove carbonate ions)
- Add aqueous silver nitrate (AgNO3(aq))
Confirmatory test: - Test solubility of precipitate in dilute/concentrated ammonia
What are the observations if chloride ions are present
- White precipitate forms
- Precipitate is soluble in dilute aqueous ammonia
What inferences can be made from the observations of chloride ions
- The precipitate is silver chloride (AgCl)
- Chloride ions are present
What is the ionic equation for the test for chloride ions
Ag+(aq) + Cl-(aq) => AgCl(s)
What are the observations if bromide ions are present
- Cream precipitate forms
- Precipitate is soluble in concentrated aqueous ammonia
What inferences can be made from the observations of bromide ions
- The precipitate is silver bromide (AgBr)
- Bromide ions are present
What is the ionic equation for the test for bromide ions
Ag+(aq) + Br-(aq) => AgBr(s)
What are the observations if Iodide ions are present
- Yellow precipitate is formed
- Precipitate is insoluble in dilute and concentrated aqueous ammonia
What inferences can be made from the observations of iodide ions
- The precipitate is silver iodide (AgI(s))
- There are I- ions present
What is the ionic equation for the test for bromide ions
Ag+(aq) + I-(aq) => AgI(s)
Describe the test for sulfate ions
- Add dilute HCl (to remove carbonate ions)
- Add aqueous barium chloride
What are the observations for a positive test for sulfate ions
A white precipitate forms.
What inferences can be made from the observations when testing for sulfate ions
- The precipitate is BaSO4(s)
- SO4(2-) ions are present
What is the ionic equation for the test for sulfate ions
Ba2+(aq) + SO4(2-)(aq) => BaSO4(s)
Describe the test for carbonate ions
Add dilute acid (e.g. HCl, HNO3 or H2SO4) to a compound or solution.
What are the observations in the test for carbonate ions
- Effervesence giving colourless gas
- Gas turns lime water cloudy
What inferences can be made from the observations in the test for carbonate ions
- Gas = CO2 (carbon dioxide)
- CO3(2-) or HCO3- ions present
What is the ionic equation for the test for carbonate ions
- CO3(2-)(s/aq) + 2H+(aq) => CO2(g) + H2O(l)
- HCO3-(s/aq) + H+(aq) => CO2(g) + H2O(l)
Describe the test for hydroxide ions
Test solution with red litmus/pH indicator.
What are the observations in the test for hydroxide ions
- Red litmus paper turns blue
- pH indicator turns blue/purple
What inferences can be made from the observations in the test for hydroxide ions
It’s alkali (and OH- ions present).
Describe the test for ammonium ions
- Add aqueous NaOH and warm mixture
- Test the gas given off with litmus or pH paper
What are the observations in the test for ammonium ions
- Gas evolved that turns damp red litmus paper blue
- Smells strongly of ammonia
What inferences can be made from the observations in the test for ammonium ions
- Alkaline gas = ammonia
- NH4+ ions present
What is the ionic equation for the test for ammonium ions
NH4+(s/aq) + OH-(aq) => NH3(g) + H2O(l)
Describe the test for group 2 ions
Add aqueous NaOH to solution of compound.
What are the observations for the test for group 2 ions
White ppt forms with Mg(2+) or Ca(2+).
What inferences can be made from the observations in the test for group 2 ions
Precipitate forming = insoluble metal hydroxide, so either Mg(2+) ions or Ca(2+) ions present.
What is the ionic equation for the test for group 2 ions
- Mg(2+)(aq) + 2OH-(aq) => Mg(OH)2(s)
- Ca(2+)(aq) + 2OH-(aq) => Ca(OH)2(s)
Describe the test for Ba(2+) ions or Sr(2+) ions
Add sulfuric acid (H2SO4) or any sulfate solution, e.g. Na2SO4
What are the observations for the test for Ba(2+) ions or Sr(2+) ions
A white precipitate forms.
What inferences can be made from the observations for the test for Ba(2+) ions or Sr(2+) ions
- Precipitate = BaSO4
- Ba(2+) or Sr(2+) ions present
What is the ionic equation for the test for Ba(2+) ions or Sr(2+) ions
Ba(2+)(aq) + SO4(2-)(aq) => BaSO4(s)
