O-Level Chemistry

[dioprem]

iamastudent:

Hi,

May I know what is the oxidation state of ions? Example like the equation:
(S2O3)2- + 4Cl2 + 5H2O --> 2(SO4)2- + 8Cl- + 10H+

What is the oxidation state of H in H+? Is it +1 or is it 0?
O in (SO4)2-? Is it -2? S in (SO4)2-? Is it +6? Thank you

The oxidation state of simple ions is always the charge of the ion. For example, in the case of H+, its oxidation state would be +1. In the case of Cl-, its oxidation state would be -1.

In the case of polyatomic ions, such as the sulfate ion, the sum of all the individual oxidation states of the atoms present in an ion must add up to the charge of the ion. In the case of (SO4)2-, the oxidation state of the 1 sulfur atom and 4 oxygen atoms must add up to -2. Oxygen generally has an oxidation state of -2. So the total oxidation state of the 4O atoms would be -8. So in order for the sulfate ion to have a charge of 2-, the S atom must have an oxidation state of +6.

Note that oxygen can have other oxidation states. For example, it will have an oxidation state of -1 in peroxide ions (O2)2-. It can also have an oxidation state of -0.5 in the case of superoxides (O2)-

Hope this helps!

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[Mojostar]

Hi all,


I’m weak in electrolysis…any way to improve in this area? Any book to recommend? Thanks.

[AdonciaTang]

Mojostar:

Hi all,


I'm weak in electrolysis...any way to improve in this area? Any book to recommend? Thanks.

Hi Mojostar. Get a tutor to help u. My niece was also failing in her Pure Chem for a year and she bought all sorts of books to read thinking it would help. It does but its so minimal. After she engaged my DS's tutor, her results improved, because now there is someone who can help to guide her along in her work and teach her the concept which she might get wrong.

[Dr.033430Daniel]

Mojostar:

Hi all,


I'm weak in electrolysis...any way to improve in this area? Any book to recommend? Thanks.

Hi Mojostar – The first thing I would recommend is to read a textbook. These three by local authors are all good:

Chemistry Insights
Chemistry Matters
Discover Chemistry

For question practice, try Conceptual Learning Chemistry by Ong Yean Ling (Blue in Color). I selected this book as a supplement to our Chemistry class worksheets because it looked to be the best one out there.

To get a handle on electrolysis, practice drawing the setups. It is a common exam question to ask you to first draw the setup and then name the products. So once you have studied the topic draw the setup several times for practice, so that you can improve your speed at doing the drawing. Then make your own notes listing all the versions of electrolysis you can find, what goes to the anode, what goes to the cathode etc. There is a logic to it that you should understand in terms of the reactivity of the various ions. But it also helps to write the reactions out a few times so that both the logic and the more common examples stick with you.

Make your notes, then test yourself a week later and see if you can remember.

[spicy]

AdonciaTang:

Mojostar:

Hi all,


I'm weak in electrolysis...any way to improve in this area? Any book to recommend? Thanks.

Hi Mojostar. Get a tutor to help u. My niece was also failing in her Pure Chem for a year and she bought all sorts of books to read thinking it would help. It does but its so minimal. After she engaged my DS's tutor, her results improved, because now there is someone who can help to guide her along in her work and teach her the concept which she might get wrong.

Hi
I have PMed you. Would it be possible to share your tutor's contact?
Thanks !

[achiever2803]

spicy:

AdonciaTang:

[quote=\"Mojostar\"]Hi all,


I'm weak in electrolysis...any way to improve in this area? Any book to recommend? Thanks.

Hi Mojostar. Get a tutor to help u. My niece was also failing in her Pure Chem for a year and she bought all sorts of books to read thinking it would help. It does but its so minimal. After she engaged my DS's tutor, her results improved, because now there is someone who can help to guide her along in her work and teach her the concept which she might get wrong.

Hi
I have PMed you. Would it be possible to share your tutor's contact?
Thanks ![/quote]Hi,

wondering if you are still looking for a tutor for chemistry. if you, do drop me a pm and i can call you to tell you the details.!

Cheers

[hopefulparent]

My son didn’t do well in Chemistry in his lower sec. Maybe it’s because he didn’t put in the effort? But it’s a compulsory subject for his school, so he has to take it this year. Thankfully, he did well for his sec 3 mid year. Proper guidance from school and tuition is very important.

[hterbin]

Mojostar:

Hi all,


I'm weak in electrolysis...any way to improve in this area? Any book to recommend? Thanks.

Electrolysis is a complicated subject with really many different scenarios. However, once you master the basic key concepts which really isn't many, electrolysis would be a really simple subject for you! Do PM me if you need any help regarding electrolysis.

[KiausuLormee]

Need help to explain this question.

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