Reaction of acids with salts

  • #1
Hi
I am new to the concept of neutralization.
My teacher told me that acids do not react with neutral salts.
I want to know why not. If both are dissolved in water and both completely dissociate, why can't the ions of acid and salt exchange and perform a double displacement reaction. Moreover I have seen a reaction in one of my books - NaCl + H2SO4 produces HCl and Na2SO4
 
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  • #2
Borek
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Do you know what the net ionic reaction is? What are spectator ions? Have you learned what the chemical equilibrium is? It is much easier to understand what is going on in these terms.

In short: when you mix solutions of HCl and Na2SO4 all you get is a mixture of ions, everything is still dissociated and no reaction takes place. Such a solution doesn't differ from the solution prepared by mixing NaCl and H2SO4.

Reaction you have seen in your book requires concentrated sulfuric acid and solid NaCl - that's quite a different situation. Besides, the most important reason why it happens is that the HCl is gaseous and volatile and can leave the reaction mixture. When you add concentrated HCl to Na2SO4 basically nothing happens.
 
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  • #3
Thank you for clearing my doubt.
In short: when you mix solutions of HCl and Na2SO4 all you get is a mixture of ions, everything is still dissociated and no reaction takes place. Such a solution doesn't differ from the solution prepared by mixing NaCl and H2SO4
Just one more thing.
What is happening in the solution when an acid reacts with a basic salt?
 
  • #4
In short: when you mix solutions of HCl and Na2SO4 all you get is a mixture of ions, everything is still dissociated and no reaction takes place. Such a solution doesn't differ from the solution prepared by mixing NaCl and H2SO4.
Can we say that MOST acid and neutral salt reactions would have a similar situation?
 
  • #5
Borek
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To be precise: most salts of strong acids and strong bases will behave this way when mixed with strong acids.

When there are weak acids/bases involved things become more complicated, that's where the acid base equilibrium comes into play.
 
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  • #6
To be precise: most salts of strong acids and strong bases will behave this way when mixed with strong acids.

When there are weak acids/bases involved things become more complicated, that's where the acid base equilibrium comes into play.
Okay got it. Thank you so much!
 
  • #7
hilbert2
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Some acids can react with some neutral salts, but then the reaction is not about exchange of ##H^+## ions. For example, mix nitric acid with potassium iodide (a neutral salt), and you get elemental iodine (##I_2##) and nitrogen oxides or ##NO_{2}^{-}## ions or something like that. In that case it's an oxidation-reduction reaction taking place.
 
  • #8
Borek
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Which is why I wrote

most salts of strong acids and strong bases
I didn't want to muddy the watter with unnecessary details.
 
  • #9
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My teacher told me that acids do not react with neutral salts.
Just to make sure that we don't talk at cross-purposes: Did he speak about salts or solutions of salts? Most of the posts are about solutions.
 
  • #10
Just to make sure that we don't talk at cross-purposes: Did he speak about salts or solutions of salts? Most of the posts are about solutions.
yes, i meant solution only. Sorry for not mentioning. :)
 

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