Qualitative analysis lab
Identify unknown cations, anions and gases at a test-tube bench: add aqueous sodium hydroxide, ammonia and the anion reagents, test any gas, and record what you see.
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Learning objectives
- describe tests to identify the following gases: carbon dioxide (using limewater); hydrogen (using a burning splint); oxygen (using a glowing splint).
- describe the use of aqueous sodium hydroxide and/or aqueous ammonia to identify the following aqueous cations through the formation of precipitates (if any) and their subsequent solubility: aluminium, ammonium (together with evolution of ammonia gas upon warming), calcium, copper(II), iron(II), iron(III) and zinc (formulae of complex ions are not required)
- describe tests to identify the following anions: carbonate (by the addition of dilute acid and subsequent use of limewater); chloride (by reaction of an aqueous solution with nitric acid and aqueous silver nitrate); nitrate (by reduction with aluminium in aqueous sodium hydroxide to ammonia and subsequent use of damp red litmus paper) and sulfate (by reaction of an aqueous solution with nitric acid and aqueous barium nitrate)
- describe tests to identify the following gases: ammonia (using damp red litmus paper); carbon dioxide (using limewater); chlorine (using damp litmus paper); hydrogen (using a burning splint); oxygen (using a glowing splint) and sulfur dioxide (using acidified potassium manganate(VII)).
- describe tests to identify the following anions: carbonate (by the addition of dilute acid and subsequent use of limewater); chloride (by reaction of an aqueous solution with nitric acid and aqueous silver nitrate); iodide (by reaction of an aqueous solution with nitric acid and aqueous silver nitrate); nitrate (by reduction with aluminium in aqueous sodium hydroxide to ammonia and subsequent use of damp red litmus paper) and sulfate (by reaction of an aqueous solution with nitric acid and aqueous barium nitrate)
- Qualitative Analysis: Cations (Table)
- Qualitative Analysis: Anions and Gases
- Qualitative Analysis Notes
Unknown 1: a solution of one cation. Nothing tested yet.
- Reagent added to this portion
- 0.00 cm³
- Portions tested
- 0
- Tests done
- 0
- Still possible
- 7
Try this
0 of 4 doneTest an unknown cation until only one ion in the Notes fits. (not done yet)
Some cations need both reagents: Al³⁺ and Zn²⁺ both give a white ppt. that dissolves in excess NaOH(aq), but only Zn(OH)₂ dissolves in excess NH₃(aq).
Test an unknown anion until only one ion in the Notes fits. (not done yet)
Each anion test is specific: a halide precipitates with acidified Ag⁺, sulfate with acidified Ba²⁺, a carbonate fizzes with acid and a nitrate gives ammonia with Al and NaOH(aq).
Identify an unknown gas with the tests for gases. (not done yet)
One test can mislead: SO₂ also turns limewater milky, so CO₂ needs limewater and SO₂ needs acidified potassium manganate(VII).
Add Ba(NO₃)₂(aq) to the carbonate without acidifying it first. (not done yet)
Barium carbonate is also a white ppt., so a carbonate could pass for a sulfate. Acidifying with nitric acid first removes carbonate as CO₂.