好多chem唔識.救命!! 我就drop得啦...~.~

1. Pure acid and acid are different.
　Pure acid means there is no any water in the acid. If the acid doesn't dissolve into the 　water, it doesn't contain H+ . However, if the aicd dissolve into the water, it ionizes 　　and products H+.

2. Calcium sulphate + Lead nitrate will form nothing.
　Because calcium sulphate cannot dissolve into the water and product any ions to 　　　occur precipitation reaction.
　Furthermore, there is no reaction between sodium sulphate and lead.
　Because sodium is more reactive than lead. So, sodium ion is not be reduced by lead!
　Moreover, if there is a reaction between two salt solution, it is not a
　displacement reaction. Because no any ions was given any electrons.

3. After Add little sodium hydroxide, the solution appears some white precipitate and
　products heat.
　If the solution was added excess of sodium hydrocide, it changes to a colorless
　solution and produces heat.

Don't drop "Chemistry" ! Which is a very interesting subject! You can get many marks from Chemistry in HKCEE or the other examination!

化學超勁!!我都唔係好識...想drop左佢...

Yea, I agree with you in large extent.

You only need memorize and calculation in this subject.

But if you are in F.5 and still don't know things taught in F.3, then drop it!

1.唔係太肯定
好似pure acid=溶落水totally dissolves
acid=溶落水未必totally dissolves
2.Ca(SO4)(aq)+Pb(NO3)2(aq)--->PbSO4(s)+Ca(NO3)2(aq)
唔知係未displacement reaction bo
3.heat given out(9成萬用)
salt are formed(acid+alkali)
water formed(acid+alkali)