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Topic: reducing agent  (Read 9344 times)

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Offline BaO

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reducing agent
« on: July 27, 2006, 04:55:38 PM »
i need your opinions , here is the question
A reducing agent will cause which of the following changes?
 
A  ClO3- --> ClO2
B  HS2O4---> H2SO3
C  H3PO3 --> H3PO4
D  NO3- --> N2O2
 
i picked C , but the answer was A, what do you think ?

thanks in advance
 

Offline Yggdrasil

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Re: reducing agent
« Reply #1 on: July 27, 2006, 05:48:42 PM »
In a redox reaction, a reducing agent becomes oxidized and the other compound in the rection becomes reduced.  Therefore, look for the reactant whose oxidation number is higher than that of the reactant.

If you look at all of the oxidation number of the reactions, you see that A is the only one in which the oxidation number of the products (the ON of the Cl is 4) is lower than the oxidation state of the reactants (the ON of the Cl is 5).  In C, the ON of P in H3PO3 is 3, whereas the ON of P in H3PO4 is 5, so this is an oxidation, not a reduction.

Offline BaO

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Re: reducing agent
« Reply #2 on: July 27, 2006, 06:54:36 PM »
but i thought reducing agent means oxidation. i dont get it.

Offline wereworm73

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Re: reducing agent
« Reply #3 on: July 27, 2006, 07:44:59 PM »
To look at it another way, a reducing agent gives up electrons while the oxidizing agent takes them.

When ClO3- was converted to ClO2, it had to take an electron.  A reducing agent could give this electron.  So, this answer was the correct one.

However, when H3PO3 was converted to H3PO4, it had to give up a pair of electrons to an oxidizing agent. 

Offline BaO

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Re: reducing agent
« Reply #4 on: July 28, 2006, 03:09:58 PM »
or maybe i dont understand the question because i think the question asks us to find which one undergoes oxidation . is it?


thank you

Offline wereworm73

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Re: reducing agent
« Reply #5 on: July 28, 2006, 03:39:18 PM »
No, the question is asking which one is the reduction reaction.  A reducing agent is going to reduce another substance, not oxidize it.

Offline BaO

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Re: reducing agent
« Reply #6 on: July 28, 2006, 03:51:22 PM »
it's so weird!, because my book says :" the oxidizing angent is reduced during the reaction . the reducing agent is oxidized during the reaction."

 i'm not gonna say anyone wrong , may be i didnt really understand the lesson?

Offline wereworm73

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Re: reducing agent
« Reply #7 on: July 28, 2006, 04:23:09 PM »
The book is correct, but I can see how that might be confusing.

So, I'll try to explain this a little differently...

When something is "reduced", it gained electrons.
And when something is "oxidized", it lost electrons.

Now when a reducing agent gives away its electrons to another substance, it's the same thing as saying that the reducing agent lost electrons, which is the same thing as saying the reducing agent was "oxidized".   Meanwhile, that other substance in the reaction was "reduced" because it gained electrons (from the reducing agent).

Likewise, when a oxidizing agent takes electrons from another substance, it's the same thing as saying that the oxidizing agent is gaining electrons, which is the same thing as saying the oxidizing agent was "reduced".  Meanwhile, the other substance in the reaction was "oxidized" because it lost electrons (to the oxidizing agent).





Offline BaO

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Re: reducing agent
« Reply #8 on: July 28, 2006, 04:28:29 PM »
so the question means for "other substance" right ? thank you very much wereworm73, i should've read the question more carefully

Offline skyglow1

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Re: reducing agent
« Reply #9 on: July 30, 2006, 01:49:04 AM »
A reducing agent reduces something else. Think about things like cleaning agent, it cleans something else. When the reducing agent reduces something else, it gets oxidized itself. In this question, they ask you which of the changes could be that "something else" that is being reduced by a reducing agent.

Looking at the oxidiation numbers, if one of the elements in the compounds has decreased its oxidation number, say from +2 to +1, then it has been reduced and that would be the answer.

Offline wave

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Re: reducing agent
« Reply #10 on: July 30, 2006, 02:27:06 PM »
how about other two answers?  I think they are also right.Is that right?

Offline wereworm73

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Re: reducing agent
« Reply #11 on: July 30, 2006, 02:56:06 PM »
Good eye, wave!

Yeah, a reducing agent would give the nitrate ion an electron to become N2O4.   And if "HS2O4" was really supposed to be H2SO4, then that too would be a reduction reaction, since the sulfur gained 2 electrons from a reducing agent.

Offline wave

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Re: reducing agent
« Reply #12 on: July 31, 2006, 01:08:56 PM »
thank you for your approval,wereworm73.
I am very glad to discuss together with you.So it seems the question itself is something wrong.

Offline BaO

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Re: reducing agent
« Reply #13 on: July 31, 2006, 03:35:37 PM »
i did check the question from the book where i got it.
youre right, it really needs to be edited again!

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