Would you look at that? Someone needs help with chem!..[equilibrium]

[kjf]

Okay, now I know I've made my fair share of these threads in my time, but I'm kinda stumped on this.

Right, did a chem prac today, writeup is due tomorrow.
I'm almost done.

Take this:

Fe3+(aq) + SCN-(aq) ⇌ FeSCN2+(aq) [damnit, why doesn't this thing allow subscript?]

Yep, equilibrium.

The equilibrium shifted to the left (in favour of the reactants) when KCl(s) was added.
Why?

Here's my idea, but I dont know if it's right.

The K+ and Cl- ions mix with the Fe3+ and SCN- ions. Therefore, lacking the 'reactants' and according to leChatelier's, the reaction will go <--.

Yet it's all in solution (there was some solid in the bottom of the test tube, something may have formed a precipetate? [bloody hope that's the case]).

If it didnt form a PPT and there was just leftover KCl on the bottom, i'm..well..i'm out of ideas.

Any help is greatly appreciated.

Thanks

edit: just checked a solubility table, chlorides form insoluble compounds with Ag and Pb...and i dont know who to check for SCN- (coz i dont bloody well know what it is)

 

[do-a-flip]

just choosing next years subjects and thankyou for helping me not to choose chem in VCE...

 

[kjf]

just choosing next years subjects and thankyou for helping me not to choose chem in VCE...

No way!
I love chem. Seriously, my favourite subject.

It's challenging at times..like now, which can always be good.

Do it.

 

[DJninja]

Man, Im so glad I don't do any science subjects. No help from me either.

 

[mike-]

re-edit.

Just having the K+ and Cl- ions in solution themselves will not change the equilibrium at all.

They will need to react to form a solid (precipitate), also, is it in a closed or open vessel?

 

[alpinestar12]

Ah chemistry.... not gonna try to help you Karl, just gonna agree with you that Chemistry is fun and a good subject to do.

 

[downhiller_1]

are you button bashing... i never liked science... chem would be so hard you doing unit 3+4

 

[kjf]

Edit: guy changed his post so I am too:

re-edit.

Just having the K+ and Cl- ions in solution themselves will not change the equilibrium at all.

They will need to react to form a solid (precipitate), also, is it in a closed or open vessel?

Yeah that's what I thought too. There was some solid in the bottom of the test tube, but this may have just been left over KCl. It's an open vessel.

Hmm. Well I'm pretty sure it changed the equilibrium? The colour changed. That sounds kinda stupid...let me explain:

The reaction above, at equilibrium (1mL of each reactant) in 50mL distilled water has a light brown/red colour to it. I dropped more Fe3+ ions into one test tube and more SCN- ions into another. Both made the solution darker (also, the product in the reaction above is a very dark red). Oh also, one of the solutions i added (which had Fe 3+ ions) was pretty yellow.

When I added KCl to the initial reaction (1mL of each), it became a light yellow colour.

Pic:

(After KCl was added)

This led me to believe that the KCl shifted the reaction towards the reactants. One of which had a yellowy colour. Also, by shifting to the reactants that decreases the amount of products (red coloured stuff). So I assumed, with the lack of red and increase in yellow..that the reaction had changed...and re-established equilibrium as in the picture.

Ah chemistry.... not gonna try to help you Karl, just gonna agree with you that Chemistry is fun and a good subject to do.

Haha oh come on. I sold you my bike, isn't that enough?

 

[mike-]

Ah, so it actually does give a FeSCN^2+ ion then?

Does than form a solid with potassium that is insoluable with water?

EDIT:

Fe^3+ irons are yellow. Your solution is yellow. Suggests the favouring of reactants.

That is what you need to explain right?

EDIT again:

Have your explored the idea of the irons changing from Fe^2+ (redish brown) to Fe^3+ (yellow).

 

[kjf]

Ah, so it actually does give a FeSCN^2+ ion then?

Does than form a solid with potassium that is insoluable with water?

I dont think KFeSCN would work..

It would be

FeSCNCl2 if anything?
(even then i dont think that exists?)

But! I want there to be either MORE products or LESS reactants produces when KCl is added. Not more products due to more reactants...




edit: Yeah that's what I need to explain. BUT! it's pretty much surface level. Why did it favour the reactants more than the products when KCl was added..I know it did (well im pretty sure) but I need to know/say WHY it did...

That's the hard part.

 

[mike-]

Igmore the bit about a positive ion bonding with a K+ ion, I meant Cl-.

The vessel is open, therefor it wont favor a particular side to keep pressure at a lowest. Forget that idea.

The only thing it could be is a precipitate forming. Nothing else would change the equlibrium.

 

[kjf]

Igmore the bit about a positive ion bonding with a K+ ion, I meant Cl-.

The vessel is open, therefor it wont favor a particular side to keep pressure at a lowest. Forget that idea.

The only thing it could be is a precipitate forming. Nothing else would change the equlibrium.

Yeah true.

But I've looked up every possible combination of the ions, and all of them form compounds that are very soluble in water.

No ppt

Shit. I'll keep researching.

thanks for the help though mate!

 

[emcgough]

the yellow precipitate would be iron chloride wouldn't it? Then you have that SCN..etc ion bonding with the K+ to form something, doesn't matter what. And due to all these products being formed, the eq shifts back right?

That is just on first impressions, I might be missing something.

edit, i mean eq shifts back to the left...

 

[kjf]

the yellow precipitate would be iron chloride wouldn't it? Then you have that SCN..etc ion bonding with the K+ to form something, doesn't matter what. And due to all these products being formed, the eq shifts back right?

That is just on first impressions, I might be missing something.

edit, i mean eq shifts back to the left...

Unfortunately, Iron(III) chloride is soluble in water.

You say SCN bonds with K...how can it? It's in solution? (I think this is where I get stuck...) Can things bond together within a solution? (an actual compound not another ion)

 

[mike-]

A polyatomic ion can yes.

Bunch of atoms with an overal charge if you don't know what polyatomic means.

 

[emcgough]

hmm, so iron chloride is soluble... then what colour is kcl and is that soluble? and what colour and solubility is KSCN (or whatever that thing would be, I can't remember)?

Also, if equilibrium shifts to the left, it is basically saying that the ion on the RHS is dissociating, which means it is being "pulled apart" by the other ions added, as I suppose they are more strongly attraced, or the bonds formed are more favourable or whatever.

It's weird.... I am definetely missing something obvious I think. The answer is not really clear to me. Will get back to you if I think of anything.

 

[kjf]

A polyatomic ion can yes.

Bunch of atoms with an overal charge if you don't know what polyatomic means.

Ah. Yeah I just looked into FeSCNCl+ ions...but google gave me 4 hits, 3 of which were some other language and one didnt give me much help..

 

[willy_c]

Unfortunately, Iron(III) chloride is soluble in water.

You say SCN bonds with K...how can it? It's in solution? (I think this is where I get stuck...) Can things bond together within a solution? (an actual compound not another ion)

I teach this lab at uni but not in the same way. The SCN would have been made up from a salt of KSCN and diluted to the concentration required. In solution you are correct it does not exist as KSCN, rather K+ and SCN-. There are a number of salts available, another is NaSCN.

 

[kjf]

hmm, so iron chloride is soluble... then what colour is kcl and is that soluble? and what colour and solubility is KSCN (or whatever that thing would be, I can't remember)?

Also, if equilibrium shifts to the left, it is basically saying that the ion on the RHS is dissociating, which means it is being "pulled apart" by the other ions added, as I suppose they are more strongly attraced, or the bonds formed are more favourable or whatever.

It's weird.... I am definetely missing something obvious I think. The answer is not really clear to me. Will get back to you if I think of anything.

Well, the thing is, in other test tubes we ad solutions of: Ferric Chloride (iron(III) chloride) and pottasium thiocyanate (that's the KSCN one). (so they are both soluble...)

Also, I think what you made a mistake? If the ions on the RHS are dissociating, then the equilibrium will want to go to the right, in order to make up for the lost ions on the RHS...

 

[willy_c]

Well, the thing is, in other test tubes we ad solutions of: Ferric Chloride (iron(III) chloride) and pottasium thiocyanate (that's the KSCN one).

Also, I think what you made a mistake? If the ions on the RHS are dissociating, then the equilibrium will want to go to the right, in order to make up for the lost ions on the RHS...

What are you actually asked to explain? What colour was the solution before you added the KCl? The Fe3+ solution should have been slightly yellow depending on the concentration, the SCN solution should have been clear and when added together the FESCN solution should be a yellow/red colour. So was it this colour before you added the KCl?