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Topic: The Voltaic Cell Zinc and Sulphuric Acid reaction  (Read 7987 times)

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Offline Mshaugh11

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The Voltaic Cell Zinc and Sulphuric Acid reaction
« on: September 26, 2012, 04:24:09 PM »

I've been studying the Zinc and Sulphuric acid simple cell (voltaic pile) reaction for the last 2 weeks, reading internet forums and text books alike. The problem i face is that every forum and textbook only goes so far and its awful fustrating. I really hope someone on this forum can take their time to simply explain the process.

Ok, so the way i see it is
Zinc atoms have 2 electrons on their outer orbital and therefore are willing to get rid of these so that they are more stable or less reactive since their outer shell will be complete i.e 8 electrons (simplistic approach and not looking at 2 x n2 calculations)

Sulphuric acid or should it be referred to as dilute sulphuric acid as it would appear that in order for the H2SO4 to be ionised, it must be diluted using H2O.

Now what actually happens with the H2O. Well according to the text books, water or H2O molecules (covalent bonds) effectively collide to form hydroxide OH -ive and hydronium H3O +ive ions. Therefore water exists as a mixture of molecules, hydroxide ions and hydronium ions.

So when the water mixture is added to the Sulphuric Acid, it become dilute and there seems to be a reaction between the H2SO4 and the H2O, the H3O +ive and the OH -ive creating an ionidised solution of +ive and -ive charged ions. 
I need to get an understanding on what actually happens here with the water ions and the sulphuric ions and how and why certain atoms are more attracted to other atoms. I need to understand why the solution eventually becomes ZnSO4 in solution. Now why is it that certain molecules i.e acids dissociate releasing a hydrogen ion without releasing a hydroxide ion and what causes this?
Looking at the formula I see the H2SO4 breaks down into H+ive and HSO4. What causes the breakdown extracting the H+ive. In the second reaction I see the HSO4 -ive breaking down into H+ive and SO4 -ive. Again why the extraction or breakoff of the H+.What actually causes this.

So now we have H2SO4 dilute = 2 H +ive   +SO4 --ive.

This ionidised solution then attracts the Zn electrons from the Zn. Now the more +ions in the solution the more Zn electrons are lost to the solution. Then these electrons attach to the H+ive thus creating H2 gas. The solution remaining is Zn ++ which dissolves into the solution and the SO4-- bond to form Zinc Sulphate ZnSO4. How are these atoms bonded?

To advance this situation, my understanding is if a copper rod is inserted into the solution (Daniell Cell) and a wire is attached between the Zn rod and the Copper rod, a current will flow or in atomic terms, the Zinc will become positive as its losing electrons and its nucleus (protons) will be more positive. How does this happen. Looking at the atomic structure and electron orbits, i can't see how the copper becomes negative to have a flow from the Zn -- to the Cu ++. 

I'm really interested to get your help and simple explanations on this matter

Offline Hunter2

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Re: The Voltaic Cell Zinc and Sulphuric Acid reaction
« Reply #1 on: September 27, 2012, 01:11:53 AM »
Simply words.

Water reacts with the hydrogen of the Sulfuric acid in two steps. Hydrogen bridge Bonding.

Finally you get

2 H2O + H2SO4 => 2 H3O+ + SO42-

More simple you write H2SO4 => 2 H+ + SO42-

This is the ionization.

For the second part Some elements are noble some ignoble. The barrier between is the hydrogen. There is a list of redox potentials. More positive means more noble.

http://en.wikipedia.org/wiki/Standard_electrode_potential_%28data_page%29

You find Zn with a value of -0.76 V. So this element is ignoble and likes to dissolve in acidic solutions and push out the hydrogen.

In the solution Zinc ions and Sulfate Ions will remain.

Offline Mshaugh11

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Re: The Voltaic Cell Zinc and Sulphuric Acid reaction
« Reply #2 on: September 27, 2012, 08:19:52 AM »
Simply words.

Water reacts with the hydrogen of the Sulfuric acid in two steps. Hydrogen bridge Bonding.

Finally you get

2 H2O + H2SO4 => 2 H3O+ + SO42-

More simple you write H2SO4 => 2 H+ + SO42-

This is the ionization.

For the second part Some elements are noble some ignoble. The barrier between is the hydrogen. There is a list of redox potentials. More positive means more noble.

http://en.wikipedia.org/wiki/Standard_electrode_potential_%28data_page%29

You find Zn with a value of -0.76 V. So this element is ignoble and likes to dissolve in acidic solutions and push out the hydrogen.

In the solution Zinc ions and Sulfate Ions will remain.

Much appreciate your response.
My background is in Engineering and therefore I dont have the understanding you have and I need an explanation on what actually happens at the atomic level with the H2O and its ions. What I understand is that their is only a very small amount of ions in the H2O solution, the rest being water molecules. So starting with this, it would appear that there arent so many ions in the dilute Sulphuric acid solution. Why then the breakdown of the Sulphuric acid as per your formulae above. What is actually causing this and why? Its the whole ionisation process from diluting the Sulphuric acid to changes that occur.

Now I understand that at the end when the solution is evaporated, we are left with ZnSO4 being held together by electrostatic forces and not bonded ionicly or covalently..hope i'm correct here.

I also believe I understand the reason why the Zn gives away its 2 electrobs on the outershell to become more stable or become closer to noble arrangement.

I hope you understand my question. By all means, please refer me to articles which may guide me through the process where you feel it necessary.

Thanks again

Offline Mshaugh11

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Re: The Voltaic Cell Zinc and Sulphuric Acid reaction
« Reply #3 on: October 01, 2012, 12:40:12 AM »
Any help in getting a detailed understanding on how and why this ionisation process works.
How and why does the sulphuric acid break up
Why does the zinc rod dissolve
Why does the zn electrode become negative if its losing electrons

Offline Hunter2

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Re: The Voltaic Cell Zinc and Sulphuric Acid reaction
« Reply #4 on: October 01, 2012, 12:51:07 AM »
Quote
How and why does the sulphuric acid break up

Its nature of this kind of molecules. I explained already that the hydrogen ions will attract to water molecules.

Quote
Why does the zinc rod dissolve

Zinc is more ignoble as hydrogen so it will be dissolved.

Quote
Why does the Zn electrode become negative if its losing electrons

The Zn ions will be dissolved, the electrons will be left on the rod. Electrons are negative so it gets negative.

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