Redox Reaction

[Lilac12]

This question isn't for homework but it was in a booklet we were given to help us revise, except we weren't given an answer booklet or worked solutions along with it. I don't even understand how to write out each side of the equation, let along do the oxidation and reduction reactions. The question is below:

"Write half-equations and hence a balance overall ionic equation for the reaction of acidified potassium dichromate solution and a solution of iron (ll) nitrate. (Note the potassium and nitrate ions are spectator ions)."

I'd really appreciate and explanation of how to get to the final answer!

[exchemist]

2 hours ago, Lilac12 said:

This question isn't for homework but it was in a booklet we were given to help us revise, except we weren't given an answer booklet or worked solutions along with it. I don't even understand how to write out each side of the equation, let along do the oxidation and reduction reactions. The question is below:

"Write half-equations and hence a balance overall ionic equation for the reaction of acidified potassium dichromate solution and a solution of iron (ll) nitrate. (Note the potassium and nitrate ions are spectator ions)."

I'd really appreciate and explanation of how to get to the final answer!

OK, why not look up dichromate on wiki and see what you find? Then let’s talk. 

[Lilac12]

Thank you for replying!

I think that I already have the empirical formula for dichromate but all I've got so far is this:

K₂CrO₇  + Fe(NO3)₂ 

I tried to search up what acidified dichromate means but I couldn't find anything, does it just mean I add H⁺   

And then I have no clue how to know which part of it will go through reduction and which will go through oxidisation. For example, a previous question in the booklet asked the same question, except it had the balanced equation given to me of:
5Fe{2+} + MnO4{-} + 8H{+} --> 5Fe{3+} + Mn{2+} + 4H2O

So I knew that the oxidation was where electrons were lost, which was:
5Fe{2+} --> 5Fe{3+} + 5e

and the reduction was where electrons were gained, which was:
MnO4{-} + 8H{+} + 5e --> Mn{2+} + 4H2O

So if I knew the whole equation I would know how to write out each half equation, so really my question is how do I do my question I posted without knowing the equation and if there is a way I'm meant to get or know the equation? 

Edited August 1 by Lilac12
Added a minus by accident

[exchemist]

14 minutes ago, Lilac12 said:

Thank you for replying!

I think that I already have the empirical formula for dichromate but all I've got so far is this:

K₂CrO₇ ^- + Fe(NO3)₂ 

I tried to search up what acidified dichromate means but I couldn't find anything, does it just mean I add H⁺   

And then I have no clue how to know which part of it will go through reduction and which will go through oxidisation. For example, a previous question in the booklet asked the same question, except it had the balanced equation given to me of:
5Fe{2+} + MnO4{-} + 8H{+} --> 5Fe{3+} + Mn{2+} + 4H2O

So I knew that the oxidation was where electrons were lost, which was:
5Fe{2+} --> 5Fe{3+} + 5e

and the reduction was where electrons were gained, which was:
MnO4{-} + 8H{+} + 5e --> Mn{2+} + 4H2O

So if I knew the whole equation I would know how to write out each half equation, so really my question is how do I do my question I posted without knowing the equation and if there is a way I'm meant to get or know the equation? 

Look up dichromate on Wiki as I suggested. If you do that, you will see that first it is an oxidising agent, plus why it is acidified, plus you will get the half reaction most commonly involved when it is used as an oxidising agent, which will tell you how many electrons it takes up per ion.

From what you have posted above, you clearly know what Fe (II) will oxidise to, and how many electrons it loses per ion.

So then you put the two together and make a reaction scheme that balances the electrons gained on the left with those lost on the right. 

Have a look in the Wiki article for the half reaction for Cr₂O₇²⁻ in acid conditions. It's not hard to spot. 

 

P.S. I'm not trying to be difficult, by the way, it's just far, far better for you to realise you can do this stuff than for us to give you the answer.🙂 The great thing with chemistry is not to get in a flap and start hyperventilating when you see chemical equations. My son used to do that - and ended up reading Ancient History. 

Edited August 1 by exchemist

[Lilac12]

Thank you so much that was really helpful, I think I've gotten to the final answer now!

[exchemist]

8 hours ago, Lilac12 said:

Thank you so much that was really helpful, I think I've gotten to the final answer now!

Splendid. 👍

I know some people are a bit sniffy about using Wiki, but I find it’s often not bad for quite a lot of physical science, and it is pretty comprehensive.

As for the half reaction of oxidising agents like dichromate and permanganate, I don’t think those are something you can expect to work out just by looking at the molecule, or ion, rather: I think you just have to know it, or look it up. These two are pretty common so it might be worth memorising them, including  the number of electrons they gain. But whether you are expected to do this or not will depend on the course you are following.

Edited August 2 by exchemist

[StringJunky]

21 hours ago, exchemist said:

My son used to do that - and ended up reading Ancient History. 

LOL!

[exchemist]

31 minutes ago, StringJunky said:

LOL!

Yes I sometimes have pangs of guilt wondering I put him off the sciences in some way. Both of his parents were on the STEM side, his late mother having been a graduate of the École Nationale des Ponts et Chausées  (though really a mathematician at heart - she later did a PhD at MIT on waves). He took physics as part of his International Baccalaureate  and did OK, but dropped chemistry after GCSE. From him I learned something interesting: chemistry is in some ways harder to grasp at the school level than physics (so long as a bit of algebra doesn't faze you)  or biology.  It has the abstraction of physics, but there is also a lot of "stuff" to just learn: the Periodic Table and the behaviour of all these different elements and compounds, not much of which seems to relate to tangible things. At least with physics you can calculate the trajectory of a cannonball, or understand the motion of the planets. 

Anyway I think he wanted to plough his own furrow and he has always been interested in the ancient world. As a matter of fact both my father and his father were historians.

[StringJunky]

24 minutes ago, exchemist said:

Yes I sometimes have pangs of guilt wondering I put him off the sciences in some way. Both of his parents were on the STEM side, his late mother having been a graduate of the École Nationale des Ponts et Chausées  (though really a mathematician at heart - she later did a PhD at MIT on waves). He took physics as part of his International Baccalaureate  and did OK, but dropped chemistry after GCSE. From him I learned something interesting: chemistry is in some ways harder to grasp at the school level than physics (so long as a bit of algebra doesn't faze you)  or biology.  It has the abstraction of physics, but there is also a lot of "stuff" to just learn: the Periodic Table and the behaviour of all these different elements and compounds, not much of which seems to relate to tangible things. At least with physics you can calculate the trajectory of a cannonball, or understand the motion of the planets. 

Anyway I think he wanted to plough his own furrow and he has always been interested in the ancient world. As a matter of fact both my father and his father were historians.

Sometimes, offspring can feel overwhelmed by their parents achievements and have more modest ambitions. One of my cousins was like that. Not everyone is cut out to think in abstract sciency/mathy ways. We are what we are. It takes all sorts to make a world. In chemistry and especially organic chem, there seems to be mountains of stuff you have to know by rote, as you said. I prefer to learn and apply principles to answer questions, rather than have to learn lots of stuff by rote, I get bored with it. My memory is not my strongest point is likely why that is. I see principles and formulae as like a Swiss knife that I can do a number of things with. I can get more out for the effort applied.

Edited August 2 by StringJunky

[exchemist]

6 minutes ago, StringJunky said:

Sometimes, offspring can feel overwhelmed by their parents achievements and have more modest ambitions. One of my cousins was like that. Not everyone is cut out to think in abstract sciency/mathy ways. We are what we are. It takes all sorts to make a world. In chemistry and especially organic chem, there seems to be mountains of stuff you have to know by rote, as you said.

Well he has his ambitions too: He's getting good grades  at St. Andrew's, in between mountaineering expeditions in the Highlands. I think he just wants to do things on his terms and carve out his own arena of expertise - very much as I did when I was his age (my mother read English so both my parents were on the arts side) The nice thing is that as I get older I become more interested in history, so I can ask him about things, which makes for a degree of academic mutual respect. 

[StringJunky]

1 minute ago, exchemist said:

Well he has his ambitions too: He's getting good grades  at St. Andrew's, in between mountaineering expeditions in the Highlands. I think he just wants to do things on his terms and carve out his own arena of expertise - very much as I did when I was his age (my mother read English so both my parents were on the arts side) The nice thing is that as I get older I become more interested in history, so I can ask him about things, which makes for a degree of academic mutual respect. 

That's good. I'm becoming more interested in history as well. I never used to like it at school. I've sort of realized that we need to know where things came from in order to know where things  are going.

[exchemist]

1 hour ago, StringJunky said:

That's good. I'm becoming more interested in history as well. I never used to like it at school. I've sort of realized that we need to know where things came from in order to know where things  are going.

Indeed. When one looks at the history of Rome, it evolves from a monarchy to a republic and then mutates into dictatorship. Ring any bells.........?

[studiot]

2 hours ago, StringJunky said:

That's good. I'm becoming more interested in history as well. I never used to like it at school. I've sort of realized that we need to know where things came from in order to know where things  are going.

+1

In my opinion History is a subject that shoud be explored when the 'student' is read, not some collection of vaguely related facts and figures rammed down a child's throat for an examination.

Having spent my working life addressing the questions 'what do I need to know or figure ?' in order to get this answer or that result I am finding in retirement the pleasure of exploring the questions ' How did we get there and what insights can be gained from this knowledge?'

I think that these insights may well be more valuable to pass on that say the details of the aerodynamics of biplanes, which knowledge in near obsolete these days.

[StringJunky]

6 hours ago, studiot said:

+1

In my opinion History is a subject that shoud be explored when the 'student' is read, not some collection of vaguely related facts and figures rammed down a child's throat for an examination.

Having spent my working life addressing the questions 'what do I need to know or figure ?' in order to get this answer or that result I am finding in retirement the pleasure of exploring the questions ' How did we get there and what insights can be gained from this knowledge?'

I think that these insights may well be more valuable to pass on that say the details of the aerodynamics of biplanes, which knowledge in near obsolete these days.

In retrospect, my exposure to the history of the British industrial revolution 1740-1940 primed me for appreciating anthropogenic climate change now. Newcomen changed everything. It meant absolutely bugger all to me in my teens. I agree that you need some decades behind you and lived some of your own history to get a proper feel for it. Time means little as a teen... like a billionaire awash with money.  

Edited August 2 by StringJunky