Sciencemadness Discussion Board - How do salt/acid reaction work?

How do salt/acid reaction work?

Dihydrogenmonoxide - 11-4-2020 at 11:58

I'm kind of struggling to understand or even find a comprehensive reference on how reactions between acids and salts work. For example NaCl/H2SO4 react but Na2SO4/HCl won't. Does it work like salt/salt reactions where the it is determined by solubility or is it related to acid strength? Also if it's Ka then why is a reaction between sulfuric acid and sodium chloride possible even though hcl has the higher Ks?

Also how does salt acidity/basicity effect these kinds of reactions?

Can someone explain it or give me a reference or some keywords to search for? I really tried to find something useful but everything i found so far is either really vague or obviously wrong ("only basic salts react with acids" - what about KNO3/H2SO4?)

DraconicAcid - 11-4-2020 at 12:55

Quote: Originally posted by Dihydrogenmonoxide

I'm kind of struggling to understand or even find a comprehensive reference on how reactions between acids and salts work. For example NaCl/H2SO4 react but Na2SO4/HCl won't. Does it work like salt/salt reactions where the it is determined by solubility or is it related to acid strength? Also if it's Ka then why is a reaction between sulfuric acid and sodium chloride possible even though hcl has the higher Ks?

I'm pretty sure that HCl is a weaker acid than H2SO4 in most solvents. However, if you react the two in dilute aqueous solution, nothing will happen.

In concentrated sulphuric acid, the reaction H2SO4 + NaCl --> NaHSO4 + HCl can be pushed forwards due to the volatility of HCl. Heat it up, the hydrogen chloride evaporates and can be removed from the system (and condenses elsewhere as hydrochloric acid. Eq'm shifts to products in order to replace it.

Texium - 12-4-2020 at 11:25

Two (three?) words: Le Chatelier’s Principle. It encompasses DraconicAcid’s explanation, and if you have a good understanding of it, you’ll be able to confidently know why metathesis reactions proceed (or don’t).

chornedsnorkack - 12-4-2020 at 23:14

Quote: Originally posted by Dihydrogenmonoxide

I'm kind of struggling to understand or even find a comprehensive reference on how reactions between acids and salts work. For example NaCl/H2SO4 react but Na2SO4/HCl won't.

Why not
Na₂SO₄+HCl->NaHSO₄+NaCl?
There are generally 4 reasons which might drive acid-salt reaction one way, 3 of which are metathesis:

1 or both products are solid precipitates (as with salts)
1 product is weak/er acid and molecular/undissociated
A product evaporates
A redox reaction happens

Note that those reasons may oppose each other and then the result depends on quantitative comparison.
For example, calcium carbonate is insoluble and chloride and nitrate are not. Yet carbonic acid is so much weaker than hydrochloric or nitric acid that reaction still happens.
Phosphoric acid is weaker than hydrochloric or sulphuric acid so these acids displace phosphoric acid from salts. Yet while hydrochloric acid boils at 110 and sulphuric at 340 degrees, phosphoric acid boils at 850 degrees, so on heating phosphoric acid displaces volatile stronger acids from salts.

Dihydrogenmonoxide - 13-4-2020 at 06:57

I get it now, really interesting. strange that it's sometimes so hard to find such simple things

pneumatician - 4-5-2020 at 18:43