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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: justastudent on March 03, 2009, 05:57:00 AM

Title: Nitric acid (liquid) - covalent or ionic substance?
Post by: justastudent on March 03, 2009, 05:57:00 AM

Hi all

I am a senior high school chemistry student in Australia. I want to do well in my exams so I can study chemistry at Uni. I wish to learn from this forum and I will also try and help out with your chemistry problems as well.

Just as I was reading on acids and bases, this question poped up.


Is liquid HNO₃ Nitric acid a covalent substance or ionic substance?


I am confused because I learnt that pure HCl (gaseous) is a colavent substance whereas HCl (aqueous) is a solution containing H⁺ ions and Cl^- ions.


Thank you for reading this post and I would appreciate any replies.

Title: Re: Nitric acid (liquid) - covalent or ionic substance?
Post by: AWK on March 03, 2009, 06:40:17 AM

read Greenwood Chemistry of the elements (2nd edition) page 465

Title: Re: Nitric acid (liquid) - covalent or ionic substance?
Post by: justastudent on March 03, 2009, 08:25:09 AM

Thanks for replying.

Unfortunately I have never heard of that text before. I hope it's common in Australia. Meanwhile, I'll try and see if the local library carries it.

Title: Re: Nitric acid (liquid) - covalent or ionic substance?
Post by: Astrokel on March 03, 2009, 10:47:00 AM

I believe it behaves the same as HCl and is polar covalent when pure HNO₃ is in liquid form.

Title: Re: Nitric acid (liquid) - covalent or ionic substance?
Post by: AWK on March 03, 2009, 11:02:08 AM

Quote from: Astrokel on March 03, 2009, 10:47:00 AM

I believe it behaves the same as HCl and is polar covalent when pure HNO₃ is in liquid form.

Unfortunately, it is more complicated problem. In fact gaseous HNO3 (though very unstable) is a covalent compound. In liquid it protonates itself (the second molecule)
HNO₃ + HNO₃ = NO₃^- + H₂NO₃⁺
Initial autoprotolysis is followed by a rapid loss of water
H₂NO₃⁺ = H₂O + NO₂⁺
water is immediately protonized
HNO₃ + H₂O = H₃O⁺ + NO₃^-
The neat reaction is:
3HNO₃ = H₃O⁺ + NO₂⁺ + 2NO₃^-

Title: Re: Nitric acid (liquid) - covalent or ionic substance?
Post by: Astrokel on March 03, 2009, 12:27:34 PM

Great info AWK, thanks. Have a snack!

Hmm, so i supposed it behaves ionic in liquid form? ::)