2.39 describe simple tests for the gases:

Gas	Test	Results
I) hydrogen (H2)	introduce lighted splint	explodes with squeaky pop
I    i) oxygen (O2)	introduce glowing splint	reignites the splint
I    ii) carbon dioxide (CO2)	bubble through lime water	goes milky white*
I    v) ammonia (NH3)	introduce moist red litmus paper	turns blue
V   ) chlorine (Cl2)	introduce moist indicator paper (any colour)	indicator paper is bleached white

Note:    The limewater goes milky because a white precipitate of insoluble calcium carbonate is formed. The equation for limewater (calcium hydroxide) reacting with carbon dioxide is:

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

2.38 describe simple tests for the anions:

2.38      describe simple tests for the anions:

i           Cl−, Br− and I−, using dilute nitric acid and silver nitrate solution

Silver chloride is insoluble in water (see Section 4.6).  Silver bromide and silver iodide are also insoluble.  Adding silver nitrate solution to a solution containing these ions will produce a precipitate of the insoluble silver halide.  The solution must be acidified in case there are any hydroxide or carbonate ions present that would also give a precipitate with the silver ions.

Take a few cm3 of the sample to be tested. Add a similar volume of dilute nitric acid. Then add a few drops of silver nitrate solution and look for a precipitate.
chloride (Cl-)	white precipitate of silver chloride Ag+(aq) + Cl-(aq) → AgCl(s)
bromide (Br-)	cream precipitate of silver bromide Ag+(aq) + Br-(aq) → AgBr(s)
iodide (I-)	yellow precipitate of silver iodide Ag+(aq) + I-(aq) → AgI(s)

ii          SO42−, using dilute hydrochloric acid and barium chloride solution

Barium sulfate is insoluble (see Section 4.6).  A white precipitate of barium sulfate will form if a solution of barium chloride is added to a solution containing sulfate ions.  The solution must be acidified in case there are any carbonate ions present that would also give a precipitate with the barium ions.  Take a few cm3 of the sample to be tested.  Add a similar volume of dilute hydrochloric acid.  Then add a few drops of barium chloride solution.

Ba2+(aq)   +   SO42−(aq)  ®     BaSO4(s)

iii         CO32−, using dilute hydrochloric acid and identifying the carbon dioxide evolved

If carbonate ions are present, carbon dioxide gas will be given off when dilute HCl is added. Take a few cm3 of the sample to be tested.  Add a similar volume of dilute hydrochloric acid.  Bubble the gas evolved through limewater and the limewater will turn milky.

This test will also work on a solid sample of a carbonate.  (See Section 4.5)

CO32-(aq) + 2H+(aq)  → CO2(g)   +   H2O(l)

2.37 describe simple tests for the cations:

Analysis of Ions and testing for gases

i           Li+, Na+, K+, Ca2+ using flame tests

To do a flame test, you need to use a piece of nichrome wire, dipped in concentrated hydrochloric acid.  Dip the wire in concentrated hydrochloric acid then place it in a roaring Bunsen flame to clean it.  Dip into the acid again, and then into the sample to be tested, and then hold in a blue Bunsen flame.  (Alternatively, use a wet wooden splint to put the sample into the flame.)  The metal ions in the compounds give different colours to the Bunsen flame:

Metal	Flame colour
lithium (Li+)	red
sodium (Na+)	yellow
potassium (K+)	lilac
calcium (Ca2+)	brick red (an orangey red)

Ii          NH4+ using sodium hydroxide solution and identifying the ammonia evolved

Add some dilute sodium hydroxide solution to a sample of the substance in a test tube and warm the mixture. Test any gas given off with moist red litmus paper.  If the substance contains ammonium ions, then ammonia gas will be given off.  The red litmus paper will turn blue, because ammonia is an alkaline gas.

NH4+(aq) + OH-(aq)  → NH3(g)   +   H2O(l)

iii         Cu2+, Fe2+ and Fe3+ using sodium hydroxide solution

Add a few drops of sodium hydroxide solution to a few cm3 of the sample to be tested.  Look for a coloured precipitate of the metal hydroxide to form.
copper(II) (Cu2+)	blue precipitate of copper (II) hydroxide Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s)
iron(II) (Fe2+)	green precipitate iron (II) hydroxide Fe2+(aq) + 2OH-(aq) → Fe(OH)2(s)
iron(III) (Fe3+)	brown precipitate iron (III) hydroxide Fe3+(aq) + 3OH-(aq) → Fe(OH)3(s)