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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: Martoman on March 13, 2010, 03:49:35 pm

Title: Oxidation number
Post by: Martoman on March 13, 2010, 03:49:35 pm: The oxidation state of
1. $Cr$ in $Fe(CrO_2)_2$ .
2. $S$ in $Fe_2(SO_4)_3$

For the first, how do you find the oxidation number of $Fe$ ? I assume its $+2$ as that is its valency, but doesn't that means that $CrO_2$ 's oxidation number has to sum to 1?

Thanks :)
Title: Re: Oxidation number
Post by: simonhu81292 on March 13, 2010, 04:06:58 pm: yeah that's right...
this is what i think ...
look inside the brac CrO2 ..if Fe is +2 ... then the oxidation number of everything inside the brac would be -1. O2 would be -4 ...so Cr would be +3
the second one SO4 is -2 ... so O4 is -8 .. S is +6
but in this case ... Fe is 3+ ... because 2 of Fe = +6.. and 3 of SO4 equals 6-// so it balances out ..
hope that helps ::)
Title: Re: Oxidation number
Post by: chem-nerd on March 13, 2010, 04:07:21 pm: because if it was Fe³⁺ then the charge on CrO₂ would need to be 1.5-, which it can't be. So assume it's Fe²⁺, thus CrO₂^-, thus ON of Cr is +3

in Q2 SO₄^2-, thus ON of S is +6
Title: Re: Oxidation number
Post by: Martoman on March 13, 2010, 04:33:18 pm: O.M.G i fail. Its not sum to 1, its sum to NEGATIVE 1 :uglystupid2: I really should have done 1-2 chem. Thanks guys.
Title: Re: Oxidation number
Post by: kyzoo on March 13, 2010, 11:11:54 pm: Wow, skipped 1-2 Chem. >.< They don't let us do 3/4 Chem at our school without doing 1/2 since apparantly you need 1/2 knowledge in order to do 3/4.
Title: Re: Oxidation number
Post by: m@tty on March 14, 2010, 12:15:19 am: Two people at my school skipped 1+2 :| 1/3rd of the class :o
Title: Re: Oxidation number
Post by: Martoman on March 14, 2010, 04:49:27 am: Quote from: m@tty on March 14, 2010, 12:15:19 am
Two people at my school skipped 1+2 :| 1/3rd of the class :o

Wow only 6 people do chem in your school?? Mine has 3 classes of 20 :crazy2:
Title: Re: Oxidation number
Post by: m@tty on March 14, 2010, 04:01:20 pm: Yeh, only 6. But there is only two from my own school, one girl and I. We go to another school for Chem, it's complicated. Same with Spesh, and there is only 6 students in that class also.(I'm the only one from my school in Spesh)
Title: Re: Oxidation number
Post by: Souljette_93 on March 14, 2010, 05:41:33 pm: Quote from: m@tty on March 14, 2010, 04:01:20 pm
Yeh, only 6. But there is only two from my own school, one girl and I. We go to another school for Chem, it's complicated. Same with Spesh, and there is only 6 students in that class also.(I'm the only one from my school in Spesh)

Why can't you do it at your school? or by distance or something..

With us, we only have 2 students for spesh, 3 for physics and 8 for chem. But we don't go to other schools or anything. i'm not even sure if we're cross marking with anyone either.

souljette<3
Title: Re: Oxidation number
Post by: m@tty on March 14, 2010, 05:43:29 pm: You have to be cross marking if there is less than 5 students in your cohort.

We go to another school because we don't have a teacher at our school who can teach the subjects.
Title: Re: Oxidation number
Post by: Souljette_93 on March 14, 2010, 05:47:19 pm: Quote from: m@tty on March 14, 2010, 05:43:29 pm
You have to be cross marking if there is less than 5 students in your cohort.

We go to another school because we don't have a teacher at our school who can teach the subjects.

Really? Are you sure?? i remember by teacher saying that they didn't cross mark when they had 3 students in the class because apparently it was too late or something. hopefully i'll confirm it with the teacher.

Souljette<3
Title: Re: Oxidation number
Post by: Martoman on March 14, 2010, 08:05:50 pm: What m@tty is saying is accurate, if you have such small numbers your cohort is joined with another school.

To be allowed to do it usually you do aptitude tests (mainly consist of: oooo look i drop ammonia in water what will happen??????).