Question about acids And molarity vs concentration

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Main Question or Discussion Point

so is an acid like HCl, is it basically these HCl ions that are "dissolved" or "infused" into water and form an acid? So what I'm saying is HCl by itself isn't possible and it's only possible in the dissolved form or aqueas form. This would make sense because as far as I know an acid or base cannot be 100% pure. And if this is true then it makes sense.

so basically, I have a few questions but the main one is. Is HCl its own pure liquid or is it just ions or a molecule dissolved in water. If it is just something in water than I won't even ask those questions because it will answer them.

Another question, which I'm almost certain the answe is no. Is it possible to have a "pure" acid?
 

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  • #2
Charles Link
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Interesting question. I was pretty sure I knew the answer, but I googled it to be sure. HCl=hydrogen chloride is a colorless gas at room temperature. And it is quite soluble in water where the ions separate (H+ and Cl-). You can get very strong concentrations, but no, you won't have pure liquid HCl (at least at atmospheric pressure). The HCl molecular bond is of the ionic form=perhaps that would explain why it separates when it encounters liquid water with the water molecule also having a permanent dipole, etc.
 
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Just to expand a little bit on Charles' answer. Even if you were to liquefy pure HCl, it wouldn't have acidic properties. HCl needs to ionize in aqueous solution in order to behave like an acid.
 
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thanks guys, it makes a lot of sense now
 
  • #5
Borek
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as far as I know an acid or base cannot be 100% pure
This is both wrong and true at the same time.

In practice there is no such thing as a "pure substance" - they are always contaminated to some extent. At the same time you can have reasonably pure sulfuric acid or nitric acid (both liquids), or pure sodium hydroxide (as a solid, or molten, if heated high enough) - what is wrong about calling them "100% pure acid" or "100% pure base"?
 
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This is both wrong and true at the same time.

In practice there is no such thing as a "pure substance" - they are always contaminated to some extent. At the same time you can have reasonably pure sulfuric acid or nitric acid (both liquids), or pure sodium hydroxide (as a solid, or molten, if heated high enough) - what is wrong about calling them "100% pure acid" or "100% pure base"?
I see what you mean, but calling it 100% pure wouldn't be right. I just read online that sulfuric acid can be 98% pure, 2% impurity seems like a big difference to me, but of course from a practical point it makes no difference. If it was some substance that was 99.99% pure i'd give it the 100%, because you're right, nothing can actually be 100% pure.
 
  • #7
Borek
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I just read online that sulfuric acid can be 98% pure
It depends on your source. 98% is a standard stock acid, one that we know to make relatively cheap, but if you need a 99.99% you can buy it too - it is just a matter of price.

Such a pure sulfuric acid is technically difficult to produce, and needs special precautions when stored, as it is highly hygroscopic and will absorb water from the air. But making it 99.99% is only a technical difficulty, there is no reason why it couldn't be done.
 
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It depends on your source. 98% is a standard stock acid, one that we know to make relatively cheap, but if you need a 99.99% you can buy it too - it is just a matter of price.

Such a pure sulfuric acid is technically difficult to produce, and needs special precautions when stored, as it is highly hygroscopic and will absorb water from the air. But making it 99.99% is only a technical difficulty, there is no reason why it couldn't be done.
Really, that's interesting. I figured it was the absolute limit
 
  • #9
Borek
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For most substances the only absolute limit is 100%.

For some things get complicated, as they are in fact an equilibrium mixture of several things, or they are unstable and can't be produced pure.

Actually it depends on how anal you want to be about what the substance is. Take water - it autodissociates, producing H+ and OH-. So technically you can argue that even 100% pure water is not "just H2O", as it contains 10-7 M of both ions. No chemist I know would think this way though.
 

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