2.28 describe a physical test to show whether water is pure.

Pure water boils at 100 ^OC and freezes at 0^OC.  You can check these to confirm the identity of the liquid.

2.27 describe the use of anhydrous copper(II) sulfate in the chemical test for water

Anhydrous copper(II) sulfate is white. It turns blue, forming the hydrated salt, when water is added.  This is an exothermic reaction.

CuSO4(s) + 5H2O(l) → CuSO4.5H2O(s)

See also section 4.23 (reversible reactions)

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)