two chemistry questions

1. The answer is (1) and (2).

(1) is correct.
Dilute dilute sulphuric acid can react with and dissolve copper(II) oxide, but cannot react with carbon.
CuO(s) + H2SO4(aq) → CuSO4(aq) + H2O
If part of the solid dissolves, the black powder is the mixture of carbon and copper(II) oxide.
If this is no observable change, the black powder is carbon.

(2) is incorrect.
Sodium hydroxide cannot react with carbon or copper(II) oxide.
No matter the black powder is carbon or the mixture of carbon and copper(II) oxide, there is no observable change.

(3) is correct.
When copper is heated strongly, it becomes red hot but remains unchanged after cooled. When carbon is heated strongly in air, it burns to form carbon dioxide.
C(g) + O2(g) → CO2(g)
If PART of the solid burns when heated strongly, the black powder is the mixture of carbon and copper(II) oxide.
If ALL of the solid burns when heated strongly, the black powder is carbon.


2. The answer is (1), (2) and (3).

(1) is correct.
Iron(II) sulphate solution is pale green in colour, but iron(III) sulphate solution is yellowish brown.

(2) is correct.
The iron(II) ion in iron(II) sulphate solution is an reducing agent, which can decolorize the deep purple potassium permanganate solution.
5Fe(aq) + MnO4-(aq) + 8H+(aq) → 5Fe3+(aq) + Mn2+(aq) + 4H2O(l)
Iron(III) sulphate contains no reducing agent, and thus it CANNOT decolourize the deep purple potassium permanganate solution.

(3) is correct.
In aqueous NH3 solution, NH3 is partly ionized in water to give OH-(aq) ion.
Iron(II) ion in iron(II) sulphate solution reacts with OH-(aq) ion to give dirty green iron(II) hydroxide precipitate.
Fe2+(aq) + 2OH-(aq) → Fe(OH)2(s)
Iron(III) ion in iron(III) sulphate solution reacts with OH-(aq) ion to give brown iron(III) hydroxide precipitate.

2009-08-18 17:32:50 補充：
貼出題目，點數已付出，刪除問題只會損人不利己。

最怕有d人志在問, 當分數係垃圾, 問到負分就開過個

真陰公.........

2009-08-20 17:50:58 補充：
有多少人是真正來學習?

來知識+問的9成都是問功課

真正去學習的就會去問老師, 而不是問我們了

世事艱難........

老子果句補充, 小弟同意

2009-08-19 19:25:57 補充：
志在問的同時, 如果真係學會了果樣知識, 都值得的