chem 2000 paper2 4條問題..

6.
Acidified KMnO4 reacts with ethene to give ethane-1,2-diol (HO-CH2CH2-OH), but does not react with ethane.
Acidified K2Cr2O7 does not react with both ethene and ethane.
In CE syllabus, acidified KMnO4 can be used to distinguished between alkene and alkane, but acidified K2Cr2O7 cannot.

17.
The aqueous solution and the molten liquid of ionic compounds can conduct electricity. During the conduction of electricity, the ionic compound is decomposed. This is known as electrolysis.

22.
H2CO3­ is a very weak acid, and it is difficult to ionize to carbonate ions. Therefore, carbonate ions have tendency to change back to H2CO3 by reacting with water to form an alkaline solution.
CO32-(aq) + 2H2O(l) ≒ H2CO3(aq) + 2OH-(aq)
This is out of CE syllabus. However, if you do not known that potassium carbonate solution is alkaline, you will also get the correct answer by other facts given in the question.

23.
Zn + 2HCl → ZnCl2 + H2

Mole ratio Zn : HCl = 1 : 2
No. of moles of Zn added = 21.8/65.4 = 0.333 mol
No. of HCl added = 2 x (250/1000) = 0.5 mol
If HCl completely reacts, no. of moles of Zn needed = 0.5/2 = 0.25 mol
Hence, Zn is in excess and HCl is the limiting reactant (completely reacted).

Mole ratio HCl : H2 = 2 : 1
No. of moles of HCl reacted = 0.5 mol
No. of moles of H2 formed = 0.25 mol
Volume of H2 formed = 0.25 x 24 = 6 dm3

(If you incorrectly take Zn as the limiting reactant, you would get the answer as 8 dm3.)
=

#23我見到20m既HCl既..囧'
份卷好似打錯左..你check下有冇..