Cr(III) ions can be reduced by?
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Basically, what is the most feasible reducing agent to reduce Cr3+ to Cr2+?
I told my student to use metal displacement method (aka. use zinc to reduce copper idea) but then there are lots of metals which can displace chromium.
So I am asking, particularly to UltimaOnline, is there any good reducing agent like (H2O2, S2O32-) which can do the same job? Basically, we are expected to use E values to deduce the feasibility of reaction.
Thanks in advance.
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Hi Uncertain,
Since the standard reduction potential of Cr3+ + e- --> Cr2+ is -0.41V, and that of Cr3+ + 3e- --> Cr is -0.74V, we need to use any reducing agent that has an oxidation potential more positive than +0.41V, but not overly positive such that it would reduce Cr3+ to Cr.
In other words, we need a reducing agent with a oxidation potential of between +0.41V and +0.74V.
You can't use zinc or hydrogen peroxide or thiosulphate ions, all of which are too strong a reducing agent and would reduce Cr3+ all the way to Cr.
Based on the list of reducing agents listed in the (SEAB issued) Data Booklet alone, there are only 3 reducing agents that can do the job. You will be able to spot them easily.
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Uncertain
You bad tuition teacher
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thanks ultima :D
lol i charged only $35/hr leh. If i know everything then is $50/hr liao. But i always assure them that i will provide them with the ans next week :p
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Originally posted by eagle:
Uncertain
You bad tuition teacher
Hehe, Eagle is just kidding lah... everyone of us could always use some help and discussion with fellow colleagues, teachers and tutors... it is also common for JC teachers to disagree with each other, but usually they don't confront each other to save (perhaps their own rather than each other's) face, but instead each teaching their own views to their students.Last year, a JC student of mine recounted how sitting in the lecture theatre, he was surprised to hear the lecturer say something outright contradictory to what his own class teacher taught. Fortunately to ease his confusion, his teacher was just sitting behind him, and as my student turned around wide-eyed to his teacher, his teacher just said, "shhh! give the lecturer some face, you all know the truth can already."
In other similar cases, the disagreeing teachers (in the same JC) usually simply instruct their students to listen to them, and ignore the other teachers' ideas. It's usually viewed as not politically acceptable to confront or argue with your colleagues.
Well, my comment is this - as 'A' level does approach University level, where there is less 'right' and 'wrong' and more of "it depends on how you see it, or interpret the question, etc", it's always possible that both teachers' views are valid - it's a matter of understanding each and applying both appropriately, rather than one must be right and the other must be wrong.
In my own school (where I taught) I often use an example of 2 HODs who hate each other, but both are universally acknowledged by students to be good, caring teachers, of the principle that when two people disagree, it doesn't mean one is right and the other is wrong, it simply means they have unique viewpoints, which is as it should be.
In the context of academia, another important piece of advice I give to my students is :
When an exam question is ambiguous and you could end up with two (or more) different answers, what should an intelligent candidate do? Ans : he should give both answers, but ensure that both answers are clearly qualified and explain.
If a student just gave two different answers without explanation, both would be marked wrong, as the marker would interpret as the student is unsure which answer is correct and is trying to cheat.
However, when the question itself is ambiguous and opens itself to two alternative answers, depending on interpretation, then the intelligent student would give both answers, carefully and clearly explaining the ambiguity and the consequent alternative answers.
I'm sure you can think of lots of examples to ambiguous questions, they pop up all the time on exam papers. Officially, if the examination markers do their job right, they would, upon marking the papers, realize the ambiguity and amend their mark scheme based on this, to accept or allow both answers. Such has been done before in Cambridge. But as you know, justice is not always done. Sometimes, students suffer for a faulty question paper and/or mark scheme.
Regardless, dear students, (at least one of) the moral of the story or take home message is this - if you receive conflicting teachings in your school from 2 different teachers, simply check with us here on The HomeWork Forum. We'll set you straight.
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Originally posted by UltimaOnline:
Hehe, Eagle is just kidding lah... everyone of us could always use some help and discussion with fellow colleagues, teachers and tutors... it is also common for JC teachers to disagree with each other, but usually they don't confront each other to save (perhaps their own rather than each other's) face, but instead each teaching their own views to their students.Last year, a JC student of mine recounted how sitting in the lecture theatre, he was surprised to hear the lecturer say something outright contradictory to what his own class teacher taught. Fortunately to ease his confusion, his teacher was just sitting behind him, and as my student turned around wide-eyed to his teacher, his teacher just said, "shhh! give the lecturer some face, you all know the truth can already."
In other similar cases, the disagreeing teachers (in the same JC) usually simply instruct their students to listen to them, and ignore the other teachers' ideas. It's usually viewed as not politically acceptable to confront or argue with your colleagues.
Well, my comment is this - as 'A' level does approach University level, where there is less 'right' and 'wrong' and more of "it depends on how you see it, or interpret the question, etc", it's always possible that both teachers' views are valid - it's a matter of understanding each and applying both appropriately, rather than one must be right and the other must be wrong.
In my own school (where I taught) I often use an example of 2 HODs who hate each other, but both are universally acknowledged by students to be good, caring teachers, of the principle that when two people disagree, it doesn't mean one is right and the other is wrong, it simply means they have unique viewpoints, which is as it should be.
In the context of academia, another important piece of advice I give to my students is :
When an exam question is ambiguous and you could end up with two (or more) different answers, what should an intelligent candidate do? Ans : he should give both answers, but ensure that both answers are clearly qualified and explain.
If a student just gave two different answers without explanation, both would be marked wrong, as the marker would interpret as the student is unsure which answer is correct and is trying to cheat.
However, when the question itself is ambiguous and opens itself to two alternative answers, depending on interpretation, then the intelligent student would give both answers, carefully and clearly explaining the ambiguity and the consequent alternative answers.
I'm sure you can think of lots of examples to ambiguous questions, they pop up all the time on exam papers. Officially, if the examination markers do their job right, they would, upon marking the papers, realize the ambiguity and amend their mark scheme based on this, to accept or allow both answers. Such has been done before in Cambridge. But as you know, justice is not always done. Sometimes, students suffer for a faulty question paper and/or mark scheme.
Regardless, dear students, (at least one of) the moral of the story or take home message is this - if you receive conflicting teachings in your school from 2 different teachers, simply check with us here on The HomeWork Forum. We'll set you straight.
Well said Ultima.
Actually this qn which i posted has been a myth to me for the past 3 yrs. Partly cos i can't be bothered and it is not significant enough to affect my A.
But anyway, this clarification has helped me a lots. Thanks Ultima, i will seek ur help more in near future.
Hope all students who visit this forum, will have a fulfilling experience :)
PS: I recommend my student to this forum today haha ;p
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Uncertain.. if u recommend him to come here... u might lose yr job.. haha
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Originally posted by arigatoast:
Uncertain.. if u recommend him to come here... u might lose yr job.. haha
As long as he score his A for chem and math, I dun mind.anyway, i have coach him for the past 10-11 mths and still i am not very satisfied with his performance. Though he score C instead of S during this period of coaching.
Well sometimes seeing your tutee score A is better than earning an extra hundreds :)