Sulfuric acid as oxidising agent

[nesstar]

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could someone plz explain the different behaviours of conc. and dilute sulfuric acids when they act as oxidising agents? thanx.

[glam7]

Concentrated sulfuric acid can react with unreactive metals such as copper and zinc making each lose 2 electrons while dilute sulfuric acid is unable to react with these unreactive metals and hence can not act as an oxidising agent on these metals unlike the concentrated form

Zn+ H2SO4 -> ZnSo4 + H2

hope it helps

[kimmeh]

do we have to know the effects of both ?

[glam7]

don't know

[mitochondria]

Zinc is quite reactive and it will in fact react with dilute H2SO4

The major difference between the reaction of concentrated and dilute sulphuric is that dilute sulphuric acid contains a large amount of H2O. When you react it with a metal such as Iron, it will hydrolysis and form rust (percipitation of Fe2O3.nH2O will appear in the solution). For concentrated sulphuric acid where the concentration of H2O is low, you will instead have a reaction where Fe(s) + conc.H2SO4[l] -----> FeSO4[aq] + H2.

The difference in their behaviour can be explained by the concentration of H2O in each of them. Note that you need O2 for rusting as well.

[mr EaZy]

i thought concentrated h2so4 can't oxidise

that is why it is transporterd at 99% conc in steel containers coz it cant oxidise steel (or iron)

only dilute h2so4 cant react with metals right????????????

[mervvyn]

Originally Posted by mr EaZy

i thought concentrated h2so4 can't oxidise

that is why it is transporterd at 99% conc in steel containers coz it cant oxidise steel (or iron)

only dilute h2so4 cant react with metals right????????????

It generally isn't transported in conc form for that reason. It is transported as H2S2O7 aka oleum, which is relatively unreactive and saves you the trouble of having to cart around water as well. The only problem is if it does touch water - very reactive!

It depends how dilute the acid is...

[mitochondria]

As mervvyn has pointed out, sulphuric acid is usually tansported as oleum, and it is produced by reacting H2SO4 with SO3:

H2SO4 + SO3 -----> H2S2O7

and converted back into H2SO4 when reacted with water:

H2S2O7 + H2O -----> 2H2SO4

Moreover, conc. H2SO4 is a stronger oxidisation agent than dilute H2SO4 and their mechanisms of reaction with metals are completely different: In dilute H2SO4, metal reacts to form the respective metal-sulphate (hydrated) salt and H2; whereas the metal-sulphate salt , SO2 and water are formed when the metal is reacted with conc H2SO4. It really wouldn't be a good idea to transport conc. H2SO4 in steel containers or you'll be watching it to turn into a pile of dark redish-brown junk I'm not sure what material they use for oleum containers, but it's probably not steel (?) since the moisture in the air is enough to turn some of the oleum into conc. H2SO4, and if those conc. H2SO4 reacts with the containers to form more water then you'll have a chain reaction going and you know what happens

Take are look at the following websites I came across:
http://www.chemistry-react.org/go/Tu...rial_4425.html
http://home.att.net/~cat6a/metals-XIII.htm

Note: for the first website, invoke the find feature of your browser and type "concentrated sulphuric acid" and it will bring you to the bit you need. You may do the same for the second one, but it has got other interesting reactions, too.

[mr EaZy]

h2so4 is tranpsorted in iron containers (in conc. form) CSU didnt mention oleum
actually tey dont ,mention H2S207 oleum anywyhere


snywaz, dilute h2so4 is transported in glass containers

[nesstar]

i thought the reason that conc can be transported in steel but not dilute is becuase of the difference in ionisation. dilute H2SO4 is more ionised and the ions will react with metal, whereas the low degree of ionisation in conc means it won't react with the metal. hence dil is transported in glass.

[mervvyn]

oleum is what my teacher taught me, and it's in conquering chem as well (p323 of mine). the reason it's used is because its nowhere near as strong an oxidant as H2S04 and it saves the trouble of carrying the water thats in dilute H2SO4.

Conc is a stronger oxidant than dilute, because it is more concentrated. The ions aren't important for the oxidation i don't think.

[Riz]

hey nesstar, its @>---
only i read this thread earlier, i won't get this question wrong in my trial. i wrote down the equation of copper reacting with sulfuric acid to show that its acting as an oxidising agent. i didnt get the mark because i didn't write it's conc. sulfuric acid. oh well i learned my lesson and won't do it again.

[Messiah19]

Hey

I found this site while i was looking for a sulfur reaction by google. mitochondria answered my question

But i have another problem regarding sulfur.

I have this question from a past paper

When h2s is bubbled into a conc sulphuric (vI) acid a white precipitate forms

explain this

H2s is a reducing agent and conc H2so4
is oxidising. I was thinking that sulfur will be formed but sulfur is not white.

What's the white precipitate?
thx

[Appleseed]

Originally Posted by mitochondria

As mervvyn has pointed out, sulphuric acid is usually tansported as oleum, and it is produced by reacting H2SO4 with SO3:

H2SO4 + SO3 -----> H2S2O7

and converted back into H2SO4 when reacted with water:

H2S2O7 + H2O -----> 2H2SO4

Moreover, conc. H2SO4 is a stronger oxidisation agent than dilute H2SO4 and their mechanisms of reaction with metals are completely different: In dilute H2SO4, metal reacts to form the respective metal-sulphate (hydrated) salt and H2; whereas the metal-sulphate salt , SO2 and water are formed when the metal is reacted with conc H2SO4. It really wouldn't be a good idea to transport conc. H2SO4 in steel containers or you'll be watching it to turn into a pile of dark redish-brown junk I'm not sure what material they use for oleum containers, but it's probably not steel (?) since the moisture in the air is enough to turn some of the oleum into conc. H2SO4, and if those conc. H2SO4 reacts with the containers to form more water then you'll have a chain reaction going and you know what happens

Concentrated sulfuric acid can be transported and stored in iron containers, as it is molecular and does not readily react with iron.
This is from HSC Online

[Undermyskin]

Exactly. This oxidizing strength totally lies within [H+]. Yet conc H2SO4 is a strong oxidant, they haven't mentioned the [] of the solution itself.