a) Recognise the results of reactions of compounds specifically mentioned in Units 1 and 2 of the specification and the results of tests for simple ions: carbonate, hydrogencarbonate, sulphate(VI), sulphite, chloride, bromide, iodide, nitrate, ammonium, lithium, sodium, potassium, magnesium, calcium, strontium and barium
| Ion
| Formula
| Test
| Observations
|
| Carbonate
| CO32-
| Test 1
Heat the solid in a test tube with a Bunsen burner.
It should decompose producing the oxide and carbon dioxide. E.g.
Test for the gas using limewater solution.
| Limewater should turn from colourless to cloudy in the presence of carbon dioxide due to precipitation of calcium carbonate.
|
Test 2
Add dilute HCl to the solid.
Test for the gas evolved using limewater solution.
| Vigorous effervescence.
Limewater should turn from colourless to cloudy in the presence of carbon dioxide due to precipitation of calcium carbonate.
|
| Hydrogencarbonate
| HCO3-
| Test
Add calcium chloride to a hydrogencarbonate solution.
| No precipitate forms since calcium hydrogencarbonate is soluble.
|
| Sulphate (VI)
| SO42-
| Test
Add barium chloride solution acidified with dilute HCl to the test solution.
| White precipitate of barium sulphate forms.
|
| Sulphite
| SO32-
| Test
Warm the sulphite with dilute HCl.
Test for gases using acidified potassium dichromate(VI) solution (or paper)
| The solution turns green.
|
| Chloride
| Cl-
| Test 1
Add concentrated sulphuric acid to the solid chloride.
| White steamy acidic fumes are seen - HCl fumes.
|
Test 2
Add dilute nitric acid to a solution of a chloride to acidify the solution. This eliminates any carbonates or sulphites.
Add silver chloride to the solution.
Add dilute ammonia solution.
|
White precipitate of AgCl forms.
Solid dissolves.
|
| Bromide
| Br-
| Test 1
Add concentrated sulphuric acid to the solid bromide.
| Steamy brownish acidic fumes are seen.
|
Test 2'
Add dilute nitric acid to a solution of a bromide to acidify the solution. This eliminates any carbonates or sulphites.
Add silver nitrate to the solution.
Add concentrated ammonia solution.
|
Cream precipitate of AgBr forms.
Solid dissolves.
|
| Iodide
| I-
| Test 1
Add concentrated sulphuric acid to the solid iodide.
| Purple acidic fumes are seen. The mixture turns to a brown slurry.
|
Test 2
Add dilute nitric acid to a solution of a iodide to acidify the solution. This eliminates any carbonates or sulphites.
Add silver nitrate to the solution.
Add concentrated ammonia solution.
| Yellow precipitate of AgI forms.
Solid is insoluble.
|
| Nitrate
| NO3-
| Test 1
Heat solid nitrate.
If group 1 solid (not Li) then will decompose to give the nitrite and oxygen.
All other solid nitrates decompose to give the metal oxide, nitrogen dioxide and oxygen.
|
Oxygen gas is evolved that will relight a glowing splint.
Brown gas is seen (NO2). Oxygen gas is also evolved and will relight a glowing splint.
|
Test 2
Boil nitrate solution with aluminium/Devarda’s alloy, in sodium hydroxide solution.
Test vapour with red litmus paper.
| Litmus paper turns blue in the presence of ammonia.
|
| Ammonium
| NH4+
|
Test
Warm ammonium compound with NaOH.
Test vapours immediately using damp red litmus paper.
| NH
3
turns the litmus paper blue.
|
| Lithium
| Li+
| Test
Dip nichrome wire in HCl.
Dip wire in solid.
Heat wire in centre of flame.
Observe colour of flame.
|
A carmine red flame is seen.
|
| Sodium
| Na+
| Test
Dip nichrome wire in HCl.
Dip wire in solid.
Heat wire in centre of flame.
Observe colour of flame.
|
A yellow flame is seen.
|
| Potassium
| K+
| Test
Dip nichrome wire in HCl.
Dip wire in solid.
Heat wire in centre of flame.
Observe colour of flame.
| A lilac flame is seen.
|
| Magnesium
| Mg2+
| Test
Add NaOH solution to the magnesium solid.
| A white solid forms which is insoluble in excess NaOH(aq). This is Mg(OH)2(s)
|
| Calcium
| Ca2+
| Test
Dip nichrome wire in HCl.
Dip wire in solid.
Heat wire in centre of flame.
Observe colour of flame.
| A brick red flame is seen.
|
| Strontium
| Sr2+
| Test
Dip nichrome wire in HCl.
Dip wire in solid.
Heat wire in centre of flame.
Observe colour of flame.
| A crimson red flame is seen.
|
| Barium
| Ba2+
| Test
Dip nichrome wire in HCl.
Dip wire in solid.
Heat wire in centre of flame.
Observe colour of flame.
| A apple green flame is seen.
|
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