HKDSE Chemistry Question Review (20250426)

Academic

#1 HTTP ERROR 404

26/04/25 00:47

Question: Hot water is poured into a cup of oatmeal. Without a mintue, the mixture is cooled down.

(a) Is the process exothermic or endothermic?

(b) Hence, explain the occurrence briefly.

#2 HTTP ERROR 404

26/04/25 00:51

Solution:

(a) The reaction is overall endothermic as heat is taken away to the oatmeal.

(b) Hydrogen bonds will form between oat macromolecules and water molecules, but the increase in potential energy between oat components offsets the bond formation. As a result, it is easy to spoon out the mixture cooled down overall.

#3 HTTP ERROR 404

26/04/25 00:55

Question: What are hypochlorite, chlorite, chlorate and perchlorate? Where are they occuring?

#4 HTTP ERROR 404

26/04/25 00:58

Solution:

They are ClO-, ClO2-, ClO3- and ClO4- ions respectively. ClO- can be found in household bleaches.

Tap water contains dissolved Chlorine and oxygen. By repeated boiling, the oxidation number of Chlorine atom increases from +0 to +7, making the solution more and more carcinogenic.

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