some questions here to ask you... -- Chemistry

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Date Posted: 04:52:35 10/31/01 Wed
Author: Chor Hoon
Subject: some questions here to ask you...

Hello Mr Yeo, i need to ask you some questions.

Tys Unit 7 Pg 7- How to do question 3c?

The textbk wrote that the elements in a particular Group have similar chemical and physical properties-then later it says that there are changes down a Group. Like the proton no. becomes bigger. Doesn't that affects the properties of the elements?

how come they say that reactive metals such as sodium can be only extracted using electrolysis? then later the textbk says that ions of reactive metals cannot be discharged and so hydrogen ions will be discharged instead. Does the discharging of hydrogen ions happen in the electrolysis of solutions only?

thank you and sorry for disturbing you.

TYS unit pg7 Question 3c- how to do? Also, the text

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[> Re: some questions here to ask you... -- Mr. Yeo Woei Ter, 06:38:46 10/31/01 Wed

First of all, I'll encouraged all of you to ask questions here, so everyone can learn at the same time.

Regarding Q3 on Topic 7 Pg.7, that question is on Reversible reaction, Chapter 14 of your textbook and is already out of the syllabus. So you can gladly skip (a) and (b) of that question EXCEPT part (c), which is a question on speed of reaction and that is STILL IN YOUR SYLLABUS!

As for your question, it is true that elements in the same Group has similar chemical and physical properties (Pg. 222 of "*textbook!"), but as we go down the group, the reactivity and physical properties of the elements changes.

For example, all Group I elements are soft metals with low melting point; and all of them react with water to form alkaline solution. That's their similarity.

But their densities generally increases down the Group while their melting points decrease down the Group. The Group I elements also become more reactive down the group. This is the trend of Group I elements.

As for your second question, reactive metals are extracted by electrolysing a MOLTEN ionic compound of the metal! (See page 252, Section 11.4, last statement, of "*textbook!")

Yes, if you electrolyse an aqueous solution of sodium chloride for example, then hydrogen ions(from water) will be discharged at the cathode, and hydrogen gas will be produced.

However, if you electrolyse MOLTEN sodium chloride, then the product at the cathode will be different. The molten compound contains only two ions, Na⁺ and Cl^- ions. Na⁺ ions will be attracted to the cathode where it will be discharged:
At the cathode: Na⁺(l) + e^- ---> Na(l)

Chloride ions will be attracted to the anode.
At the anode: Cl^-(l)---> Cl(g) + e^-
Cl(g) + Cl(g) ---> Cl₂(g)

Thus, this electrolysis will yield sodium metal at the cathode and chlorine at the anode.

Hope that answers your question!

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