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[化學 Chem] HKDSE Chemistry Question Review (2019-09-05)



HKDSE Chemistry Question Review (2019-09-05)

[隱藏]
140664_GettyImages-181874097.jpg
Let's see HKEAA's style on HKALE Chemistry:

In paper 1, there is a reading comprehension section.
With a reading passage, any out-C items can become in-C response.

So I would like to offer enrichment materials for DSE-goers,
in a sense that they can bridge the knowledge to freshman level.

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引用:
What will happen if you let an aqueous FeSO4 idle in room temperature for a couple of days?


This is disproportionation reaction apart from halogen's one.

In halogens,
we can find that the element will perform heterolytic fission.
e.g. Cl2 (g) + H2O(l) --> HCl(aq) + HOCl(aq)
such that the oxidation number of halogen becomes
0 (from Cl2) = [+1] (from HOCl) + [-1](from HCl)

In metal,
we know that Fe[2+] is reducing agent and thus unstable.
Then we have:

3Fe[2+] --> 2Fe [3+] + Fe(s)

So you will see the precipitate further rusted into Fe3O4

Note that

Fe3O4 (s) = FeO (s) + Fe2O3(s)

The solution will turn from green to reddish brown.

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引用:
Isomerism of elements is called allotropism.
How about this for Carbon, Phosphorus, Oxygen and Sulphur?


Allotropes-of-Phosphorus-Allotropes-of-Oxygen.jpg

Allotropes_Of_Carbon.png

For sulphur, something special:

allotropes of sulfur 3.JPG
allotropes-8-638.jpg




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引用:
Brief the isomerism of SO3

In room temperature, SO3 is a monomeric gas.
main-qimg-2147aa2b8736e86e9299c32b17e505ba.jpg
By dative bonding, it can form (SO3)3 or even polymers.
剪貼簿-1.png
The trimer has the following structure:
1024px-Sulfur-trioxide-trimer-from-xtal-1967-3D-balls-B.png

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[隱藏]
引用:
Why is Fe(NO3)2 (aq) an acidic salt?

Fe(NO3)2(s) + H2O(l) --> Fe(OH)2 + 2 HNO3
Note that Fe(OH)2 is a weak base while HNO3 is a strong acid.
In fact, this is a kind of complex salt such that OH[-] ion does not fully dissociate.
Fe(H2O)6SO4.png

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Footnote

Below is an Advanced Placement (AP) level chemistry reference:
https://www.khanacademy.org/science/chemistry
It does include many things even not included in HKALE.

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