Qualitative analysis Flashcards
Reagent for carbonate test
Any acid
Products for carbonate test with acid
Carbon dioxide and water
Observation for carbonate test
Effervesence (CO2(g))
To confirm the gas is carbon dioxide…
…bubble through limewater.
What is limewater?
A saturated solution of calcium hydroxide, Ca(OH)2(aq).
Carbon dioxide and limewater reaction products
White precipitate of calcium carbonate (CaCO3)
BaSO4 in water is very…
…insoluble.
Reagent used in sulfate test
Soluble barium compound, e.g; Ba(NO3)2(aq)
Reagent for halide test
Acidified silver nitrate solution: AgNO3(aq)
Ionic equ between chloride and silver nitrate
Ag+(aq) + Cl-(aq) …. AgCl(s)
Colour of precipitate for chloride and silver nitrate reaction
White
Solubility of AgCl(s) in NH3(aq)
Soluble in dilute NH3(aq)
Ionic equ between bromide and silver nitrate
Ag+(aq) + Br-(aq) …. AgBr(s)
Colour of precipitate for bromide and silver nitrate reaction
Cream
Solubility of AgBr(s) in NH3(aq)
Soluble in concentrated NH3(aq)
Ionic equ between iodide and silver nitrate
Ag+(aq) + I-(aq) …. AgI(s)
Colour of precipitate for iodide and silver nitrate reaction
Yellow
Solubility of AgI(s) in NH3(aq)
Insoluble on concentrated NH3(aq)
Sequence of tests
- Carbonate test: CO3^2-
- Sulfate test: SO4^2-
- Halide test: Cl-, Br-, I-
Only carbonate produce…
…bubbles of gas wen an acid is added.
What is expected when Ba^2+(aq) ions are added?
A white precipitate of barium sulfate will form, if SO4^2(aq) ions are present.
Describe a false positive for the sulfate test
If carbonate ions are present, a white precipitate of barium carbonate, BaCO3(s), will form as it is also soluble. This is a flase positive.
What is expected when Ag+(aq) are added to a halide solution?
A precipitate of a silver halide is expected.
What happens if a carbonate or sulfate are present in a halide test?
A precipitate will be seen as CO3^2- and SO4^2- are also insoluble.
Describe the carbonate test
Add any acid until effervesence stops. Effervesence shows carbonate present. Adding the acid to excess removes the carbonate prior to the sulfate test.
Why is acid added in excess during the carbonate test?
To remove all the carbonate prior to the sulfate test.
Describe the sulfate test
Add barium nitrate,. Any white precipitate formed (indicating the presence of a sulfate) should be removed via filtration.
Describe the halide test
Add silver nitrate solution. A precipitate will form if a halide is present. Add ammonia solution to confirm which halide it is.
Reagent to test for ammonium- NH4+
Sodium hydroxide, NaOH(aq)
Describe the test for identifying ammonium
Heat aqueous ammonium ions and aqueous hydroxide ions together as they will react to form ammonia gas, NH3(g).
Obs for ammonium test
Ammonia gas is produced which turns damp red litmus paper blue.
Ionic equ for ammonium test
NH4+(aq) + OH-(aq) …. NH3(g) + H2O(l)
Colour of copper II (Cu2+) solution
Blue
Colour and formula of copper II (Cu2+) precipitate
Light blue
Cu(OH)2(s)
Colour of iron III (Fe3+) solution
Pale yellow (pale violet)
Colour and formula of Fe3+ precipitate
Rusty brown
Fe(OH)3(s)
Colour of iron II Fe2+ solution
Pale green
Colour and formula of Fe2+ precipitate
Green, goes orange/brown when exposed to air.
Fe(OH)2(s) / Fe(OH)3(s)
Colour of maganese II Mn2+ solution
Very pale pink, virtually colourless
Colour and formula of Mn2+ precipitate
Pale brown. Surface darkens on exposure to air.
Mn(OH)2(s) / Mn(OH)3(s)
Colour of chromium III Cr3+ solution
Green
Colour and formula of Cr3+ precipitate
Green/grey. Dissolves in excess to form green solution.
Cr(OH)3(s) / [Cr(OH)6]^3-(aq)
