Off-Topic : Chemistry Question

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Off-Topic : Chemistry Question

Postby Goins2754 » Wed Nov 03, 2010 7:16 am

I had a question on an exam today that stumped me. Basically, NaOH reacts with H2SO4 to form what?

My answer was H3O & Na2SO4. Now, I said H3O because we're discussing acids and bases and probably 90% of the chemical equations involve hydronium or hydroxide in some fashion.

The correct answer, of course, is H2O & Na2SO4.

Why is this water instead of hydronium?

Thanks!

(BTW, I thought I'd put the "off-topic" header for this forum to the test. If these types of posts are unwelcome here, just let me know and I won't do it again.)
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Re: Off-Topic : Chemistry Question

Postby Mutley » Wed Nov 03, 2010 7:44 am

2 NaOH + H2SO4 => H3O + Na2SO4

would be impossible because there are a hydrogen and oxygen atom missing after the reaction.

edit: those 2 form OH- and then that would react with H3O+ to form 2 water molecules.


2 NaOH + H2SO4 => 2 H2O + Na2SO4

That would be possible afaik.
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Re: Off-Topic : Chemistry Question

Postby isiz » Wed Nov 03, 2010 7:51 am

Been forever since I took chemistry, but I would suspect it has to do with the strength of the molecular bonds.
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Re: Off-Topic : Chemistry Question

Postby Kuripari » Wed Nov 03, 2010 7:57 am

Ya, essentially, an acid and a base will react to form the products of a water and a salt. Although yes, even pure water will dissociate to form hydronium and hydroxide, because it is equilibrium to each other, and because its not a part of the reaction, it's not included. In this case, sodium hydroxide and sulfuric acid, produce water, and sodium sufate.
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Re: Off-Topic : Chemistry Question

Postby Goins2754 » Wed Nov 03, 2010 8:07 am

Mutley wrote:2 NaOH + H2SO4 => H3O + Na2SO4

would be impossible because there are a hydrogen and oxygen atom missing after the reaction.

edit: those 2 form OH- and then that would react with H3O+ to form 2 water molecules.


2 NaOH + H2SO4 => 2 H2O + Na2SO4

That would be possible afaik.


Ah, that makes a lot of sense. Gah. I wish I'd thought of it like that. I probably spent 15 min trying to balance this stupid thing with H3O. If I'd just looked at it like "I need another OH" then the water would have been the obvious choice.

Oh, well. I still think I got an A on the exam.

Thanks for the help!
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Re: Off-Topic : Chemistry Question

Postby Malthrax » Wed Nov 03, 2010 8:08 am

Kuripari wrote:Ya, essentially, an acid and a base will react to form the products of a water and a salt. Although yes, even pure water will dissociate to form hydronium and hydroxide, because it is equilibrium to each other, and because its not a part of the reaction, it's not included. In this case, sodium hydroxide and sulfuric acid, produce water, and sodium sufate.


... and a whole lotta heat, possibly even an explosion of the quantities are large enough.

Strong Acid + Strong Base = violent reaction
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Re: Off-Topic : Chemistry Question

Postby Cronus » Wed Nov 03, 2010 9:44 am

Goins2754 wrote:I had a question on an exam today that stumped me. Basically, NaOH ....


You lost me at NaOH... :?
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Re: Off-Topic : Chemistry Question

Postby Rojhaz » Wed Nov 03, 2010 10:44 am

Cronus wrote:
Goins2754 wrote:I had a question on an exam today that stumped me. Basically, NaOH ....


You lost me at NaOH... :?

Sodium Hydroxide!

It's been 10 years since I took chemistry and I wasn't very good at it; I'm glad there are more knowledgeable chemistry people around.
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Re: Off-Topic : Chemistry Question

Postby Chunes » Wed Nov 03, 2010 11:04 am

I somehow managed to pass the AP chemistry exam in HS, yet this is still chinese to me after all these years.

:(
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Re: Off-Topic : Chemistry Question

Postby tlitp » Wed Nov 03, 2010 11:10 am

Goins2754 wrote:Basically, NaOH reacts with H2SO4 to form what?

It depends on the solvent. :P
If you throw anhydrous/dessicated NaOH over anhydrous H2SO4, the dominant species will be sodium/hydrons (as cations) and HSO4/HS2O7 (as anions).
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Re: Off-Topic : Chemistry Question

Postby Goins2754 » Wed Nov 03, 2010 11:14 am

tlitp wrote:
Goins2754 wrote:Basically, NaOH reacts with H2SO4 to form what?

It depends on the solvent. :P
If you throw anhydrous/dessicated NaOH over anhydrous H2SO4, the dominant species will be sodium/hydrons (as cations) and HSO4/HS2O7 (as anions).


Oh, well let me preface my previous question with "I'm in Chem 101 and..."

:)
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Re: Off-Topic : Chemistry Question

Postby Epimer » Wed Nov 03, 2010 12:03 pm

Answered in the first reply, but to maybe help out in the future:

The correct answer was balancing the equations, as was pointed out. The clue was that H2SO4 is a diprotic acid - it has 2 potentially acidic protons per molecule. NaOH, however, only has the one hydroxide ion per molecule. To make a balanced equation, you're necessarily going to need twice as many molecules of NaOH to completely react with every molecule of H2SO4.

If that didn't make things any clearer, don't worry! It's just a very slightly more qualitative way of thinking about the equation.
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Re: Off-Topic : Chemistry Question

Postby masterpoobaa » Wed Nov 03, 2010 4:01 pm

Eprimers got it.

As Sulphuric acid is di-protic (H2) you need 2x the amount of NAOH to neutralise it

2 NaOH + H2So4 -> 2 H2O + Na2SO4 + HEAT

But this is simplified as Na2SO4 is not a solid but exists as disolved ions.
Namely 2 Na(+) SO4(2-)
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Re: Off-Topic : Chemistry Question

Postby Epimer » Wed Nov 03, 2010 4:08 pm

masterpoobaa wrote:But this is simplified as Na2SO4 is not a solid but exists as disolved ions.
Namely 2 Na(+) SO4(2-)


Not to go all tlitp on you ( :P ) but this is only correct for the assumed case of aqueous solvent. I only nit-pick because Na2SO4 certainly is a solid when not in aqueous solution. It's commonly used as a dessicant in organic chemistry labs.
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Re: Off-Topic : Chemistry Question

Postby masterpoobaa » Wed Nov 03, 2010 10:32 pm

Of course.
But in this case the acid and base addition would HAVE to occur in an aqueous solution.

Unless someone is brave enough to add crystallised 100% NaOH to Concetrated Sulphuric acid :mrgreen:

FIZZ!
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