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Old 11-13-2014, 09:25 AM   #9901
liampje
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How does sulfate reduction work exactly? In the sense of how can hydrogen sulfide form while the reaction between iron and sulfuric acid is going on?

So far I think it's actually the hydrogen-ions reacting with the sulfate-ions while forming hydrogen sulfide and oxygen. But I highly doubt it.

What is more likely is that sulfate ions reducts to HS-, SO3 2- or SO2. And then reacts further to H2S. But what does it reduct to and how do I know to what it reducts?

EDIT: I found that elemental sulfur can react to H2S if there is a reductor. There is a reductor, Iron.

But then I still need to know how sulfate reacts to elemental sulfur and something with oxygen (Ionic oxygen or elemental oxygen)

Last edited by liampje : 11-13-2014 at 09:38 AM.
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Old 11-13-2014, 09:40 AM   #9902
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Originally Posted by liampje
How does sulfate reduction work exactly? In the sense of how can hydrogen sulfide form while the reaction between iron and sulfuric acid is going on?

So far I think it's actually the hydrogen-ions reacting with the sulfate-ions while forming hydrogen sulfide and oxygen. But I highly doubt it.

What is more likely is that sulfate ions reducts to HS-, SO3 2- or SO2. And then reacts further to H2S. But what does it reduct to and how do I know to what it reducts?

EDIT: I found that elemental sulfur can react to H2S if there is a reductor. There is a reductor, Iron.

But then I still need to know how sulfate reacts to elemental sulfur and something with oxygen (Ionic oxygen or elemental oxygen)


In what context are we talking here? Some kind of sulfur reducing bacteria? Or is it a spontaneous reaction?

EDIT: I'm guessing spontaneous then.

EDIT2: Oh my god I haven't done this shit in ages.

EDIT3: Turning SO4 2- into H2S would be a pretty extensive process. I really doubt it happens simply in the presence of iron and oxygen. Bacteria can do it though, because enzymes are awesome. Maybe I'm misunderstanding something but can you really spontaneously reduce sulfate to H2S? I wanna know the answer to this.

Last edited by RedDeath9 : 11-13-2014 at 10:21 AM.
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Old 11-13-2014, 10:02 AM   #9903
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Originally Posted by liampje
How does sulfate reduction work exactly? In the sense of how can hydrogen sulfide form while the reaction between iron and sulfuric acid is going on?

So far I think it's actually the hydrogen-ions reacting with the sulfate-ions while forming hydrogen sulfide and oxygen. But I highly doubt it.

What is more likely is that sulfate ions reducts to HS-, SO3 2- or SO2. And then reacts further to H2S. But what does it reduct to and how do I know to what it reducts?

EDIT: I found that elemental sulfur can react to H2S if there is a reductor. There is a reductor, Iron.

But then I still need to know how sulfate reacts to elemental sulfur and something with oxygen (Ionic oxygen or elemental oxygen)



Ill get back to you.

Last edited by DamienEx1021 : 11-13-2014 at 10:03 AM.
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Old 11-13-2014, 03:10 PM   #9904
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Is anyone here good with calculus? Lagrange multipliers specifically, if so then I think I'm going to be asking for a bit of help at some point soon. I'm getting the basics but its really pushing my skills to the limit and I'm finding it very difficult

I did them a year and a half ago.. PM me if you can't get help here since I don't check this thread that often.
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Old 11-14-2014, 06:20 AM   #9905
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Originally Posted by RedDeath9
In what context are we talking here? Some kind of sulfur reducing bacteria? Or is it a spontaneous reaction?

EDIT: I'm guessing spontaneous then.

EDIT2: Oh my god I haven't done this shit in ages.

EDIT3: Turning SO4 2- into H2S would be a pretty extensive process. I really doubt it happens simply in the presence of iron and oxygen. Bacteria can do it though, because enzymes are awesome. Maybe I'm misunderstanding something but can you really spontaneously reduce sulfate to H2S? I wanna know the answer to this.


It happens spontaneously. Or there are sulfate reducing bacteria present everywhere. But I highly doubt the latter. We just added ironpowder to a sulfuric acid sollution. The only thing we did next to that was bringin it up to about 80 degrees. celsius.

If there was a magical reaction which converts sulfate ions into molecular sulfur I have found the two reactions. One in which sulfate breaks down in sulfur and another redoxreaction where hydrogensulfide forms.
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Old 11-14-2014, 08:25 AM   #9906
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Aw ye chemistry. Hold on I have an entire stack of notes on various sulphur compounds and the 'connections' between them, I'll see if there's anything to add.
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Old 11-14-2014, 01:57 PM   #9907
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Originally Posted by liampje
How does sulfate reduction work exactly? In the sense of how can hydrogen sulfide form while the reaction between iron and sulfuric acid is going on?

So far I think it's actually the hydrogen-ions reacting with the sulfate-ions while forming hydrogen sulfide and oxygen. But I highly doubt it.

What is more likely is that sulfate ions reducts to HS-, SO3 2- or SO2. And then reacts further to H2S. But what does it reduct to and how do I know to what it reducts?

EDIT: I found that elemental sulfur can react to H2S if there is a reductor. There is a reductor, Iron.

But then I still need to know how sulfate reacts to elemental sulfur and something with oxygen (Ionic oxygen or elemental oxygen)


I've looked into it and everyone else is right, what context are we talking about here?

----------------------------------

Iron metal dissolves readily in dilute sulphuric acid in the absence of oxygen to form solutions containing the aquated Fe(II) ion together with hydrogen gas, H2. In practice, the Fe(II) is present as the complex ion [Fe(OH2)6]2+.

Fe(s) + H2SO4(aq) → Fe2+(aq) + SO42-(aq) + H2(g)

If oxygen is present, some of the Fe(II) oxidizes to Fe(III).

----------------------------------


This is the reaction if it is just Iron and Sulfuric Acid. Water is also required for this reaction otherwise the complex cannot form and iron will remain in solid form. This is to say if you have 100% pure sulfuric acid you wont react with iron, but since this is unlikely, you should get a reaction.

Even if you take iron oxide, Fe2O3 or FeO, and react that with sulfuric acid, you are left with Fe2(SO4)2 and H2O (or possibly FeSO4 depending on the oxidation state of iron).

If you end up with solid Fe2(SO4)3 and you heat it, you could break it down to FeO and SO3, but you still don't end up with H2S.

The only information I found about plain sulfates breaking down into H2S were with regards to bacteria, which is outside my realm of knowledge. What I did read up on though had no mention of sulfuric acid.

Last edited by DamienEx1021 : 11-14-2014 at 07:15 PM.
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Old 11-14-2014, 05:26 PM   #9908
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Originally Posted by DamienEx1021
I've looked into it and everyone else is right, what context are we talking about here?

----------------------------------

Iron metal dissolves readily in dilute sulphuric acid in the absence of oxygen to form solutions containing the aquated Fe(II) ion together with hydrogen gas, H2. In practice, the Fe(II) is present as the complex ion [Fe(OH2)6]2+.

Fe(s) + H2SO4(aq) → Fe2+(aq) + SO42-(aq) + H2(g)

If oxygen is present, some of the Fe(II) oxidizes to Fe(III).

----------------------------------

Now I have no idea where you found that iron is a reducer, because the solid Iron is losing electrons and not gaining them. Iron undergoes oxidation, not reduction. Now if you are talking about Fe(II) or Fe(III) then those could act as reducers, but I am fairly sure that the equilibrium favors the ionic products in solution.


That's the definition of reducer, reducing agent, etc. It loses electrons (becomes oxidized), and reduces other species.

liampje, are you thinking that something has to gain hydrogen to be considered "reduced?" I think you just look at the oxidation states of different species and see how they've changed. In this equation:

Fe(s) + H2SO4(aq) → Fe2+(aq) + SO42-(aq) + H2(g)

Iron goes from having an oxidation state of 0 to 2+ or 3+ i.e. it has lost electrons, therefore become oxidized. Which species gained those electrons, then? Well, I'd say it was the hydrogen atoms, they went from being +1 to 0. The SO4 2- charge didn't change, so I wouldn't even call this sulfate reduction... At least that's my understanding of it?

SO4 2- needs to act as an electron acceptor before it can be reduced in the way that you're talking about. You need to get rid of all these bonds:



I don't know if you've done any resonance structures, organic chemistry, etc. but this molecule is really stable, and it won't spontaneously turn into H2S. Basically what I'm saying is... Something really negatively charged has to attack the S atom, and push off an O atom, and it has to do that over and over again until it's H2S, and this, as far as I know... is pretty complex. It can be done using a ton of enzymes.

Last edited by RedDeath9 : 11-14-2014 at 05:37 PM.
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Old 11-14-2014, 07:14 PM   #9909
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Quote:
Originally Posted by RedDeath9
That's the definition of reducer, reducing agent, etc. It loses electrons (becomes oxidized), and reduces other species.


Damnit... I mixed that up. This is what I get for posting shit half asleep at work >.<

I kept saying to myself "gain of electrons reduced" "loss of electrons oxidized" and I have no effing clue how I came up with my stupid statement.

At least that is the only thing I was bassackwards in.


EDIT: With regards to the rest of your post, I think you hit the nail on the head. You took way more time to explain it then I did.

This is what happens when I work with polymers for too long. I forget the simple easy crap

Last edited by DamienEx1021 : 11-14-2014 at 07:18 PM.
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Old 11-16-2014, 09:38 AM   #9910
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Originally Posted by RedDeath9
That's the definition of reducer, reducing agent, etc. It loses electrons (becomes oxidized), and reduces other species.

liampje, are you thinking that something has to gain hydrogen to be considered "reduced?" I think you just look at the oxidation states of different species and see how they've changed. In this equation:

Fe(s) + H2SO4(aq) → Fe2+(aq) + SO42-(aq) + H2(g)

Iron goes from having an oxidation state of 0 to 2+ or 3+ i.e. it has lost electrons, therefore become oxidized. Which species gained those electrons, then? Well, I'd say it was the hydrogen atoms, they went from being +1 to 0. The SO4 2- charge didn't change, so I wouldn't even call this sulfate reduction... At least that's my understanding of it?

SO4 2- needs to act as an electron acceptor before it can be reduced in the way that you're talking about. You need to get rid of all these bonds:



I don't know if you've done any resonance structures, organic chemistry, etc. but this molecule is really stable, and it won't spontaneously turn into H2S. Basically what I'm saying is... Something really negatively charged has to attack the S atom, and push off an O atom, and it has to do that over and over again until it's H2S, and this, as far as I know... is pretty complex. It can be done using a ton of enzymes.

But the point is. It happened. And we didn't add anything but sulfuric acid and iron powder. It happened.
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Old 11-16-2014, 10:16 AM   #9911
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Originally Posted by liampje
But the point is. It happened. And we didn't add anything but sulfuric acid and iron powder. It happened.


What made you think it happened? Did you measure it somehow?

Last edited by RedDeath9 : 11-16-2014 at 10:20 AM.
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Old 11-16-2014, 02:31 PM   #9912
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Originally Posted by liampje
But the point is. It happened. And we didn't add anything but sulfuric acid and iron powder. It happened.


How? Evidence? What did you use to measure it? Was it iron powder or iron oxide? What laboratory conditions? Did you have a catalyst or accelerator?

If all you had was Iron and Sulfuric Acid, you did not produce H2S. Period. At least not under STP and other standard conditions.

Are we missing something here?
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Old 11-17-2014, 03:53 PM   #9913
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It is in my book. It is one of the questions, I need to answer it. My teacher told me that it would've formed and we would've smellt it. But we let the reaction take place in one of those cabinets that sucks off air.
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Old 11-17-2014, 05:10 PM   #9914
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Plain elemental iron will react with sulfuric acid but it will not produce hydrogen sulfide. There is no questioning or arguing the points to this. This is fact. This is what happens.

You are either leaving out a very critical detail of what you did in the lab, the question is miss leading, or your teacher is flat out wrong. Take a picture of the question and upload it here and we might be able to help more. But as it stands, there is nothing here that you are telling us that makes any sense.

I don't know what else to tell you.
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Old 11-18-2014, 05:28 AM   #9915
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Originally Posted by DamienEx1021
Plain elemental iron will react with sulfuric acid but it will not produce hydrogen sulfide. There is no questioning or arguing the points to this. This is fact. This is what happens.

You are either leaving out a very critical detail of what you did in the lab, the question is miss leading, or your teacher is flat out wrong. Take a picture of the question and upload it here and we might be able to help more. But as it stands, there is nothing here that you are telling us that makes any sense.

I don't know what else to tell you.

The question says something along the lines of:
''You may have smellt the smell of rotten eggs during this synthesis. This is the smell of an unwanted product that forms, H2S. Where does this smell come from? Take another look at the substances used in the synthesis.''

Probably my practice teacher just read the book and said it developed. There are some other things I disagree with him. For instance: He said that if you use Phenolphtalein as indicator in an acid-base titration, the fact that the pH of color change is 8,2 will not affect the resulting outcome in amount of acid.

It will, because at pH 8,2 there is already hydroxide-ions ''taking over''. Even though it's just one drop of base. He also said that if you add water to the sollution of acid, it doesn't matter. But it does as well, because it will take more hydroxide-ions to get a pH-value of 8,2.
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Old 11-18-2014, 10:59 AM   #9916
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Originally Posted by liampje
The question says something along the lines of:
''You may have smellt the smell of rotten eggs during this synthesis. This is the smell of an unwanted product that forms, H2S. Where does this smell come from? Take another look at the substances used in the synthesis.''


What EXACTLY were you using in the synthesis? Chemical names and everything.

Quote:
Probably my practice teacher just read the book and said it developed. There are some other things I disagree with him. For instance: He said that if you use Phenolphthalein as indicator in an acid-base titration, the fact that the pH of color change is 8,2 will not affect the resulting outcome in amount of acid.

It will, because at pH 8,2 there is already hydroxide-ions ''taking over''. Even though it's just one drop of base. He also said that if you add water to the solution of acid, it doesn't matter. But it does as well, because it will take more hydroxide-ions to get a pH-value of 8,2.


No, it really doesn't matter. Not for practical purposes anyway. Indicators are really a shot in the dark. For what you are doing in a lab there is no issue. In the real world when people are doing titrations, they use an auto-titrator and there is no indicator involved.

Adding water to the solution doesn't matter either. But this is for a weird reason. Lets say you have 50mL of 1M HCl and you add 50mL of H2O. The concentration changes yes, but you still have the same amount of H+ ions left in solution that you need to neutralize before you hit the Eq point. The only thing that will have changed is the volume. So now you have 100mL of 0.5M HCl vs 50mL of 1M HCl. Do the math, it will take the same amount of base to neutralize both.
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Old 11-19-2014, 05:58 AM   #9917
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We were using Fe, H2SO4 and water used for solving H2SO4.

Now, I do not have any info about the brands, because they were not in the pot they came with. The sulfuric acid was already dissolved in a brown flask. But assuming the other chemicals I've used in the past, it will probably be vwr chemicals.

And I know the amount of reactant stays the same, but if you use an indicator, it will change the actual volume in which you can see that the equivalation point has been reached. But this is minimal.
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