Chem acidic salt question (1 Viewer)

[BOS Secret Service]

First thing:

How come "acid + base --> salt + water" does not apply to HCl + NH₄ -->NH₄Cl

Second Thing:

For the 2006 HSC Chem paper, in Q21, "Explain the acidic nature of the salt you selected (I selected Ammonium Chloride). Include a balanced equation in your answer."

The success one Answers say:

"When ammonium chloride is dissolved in water it dissociates into its ions, NH₄⁺ and Cl^-.
Cl^- is the weak conjugate of the strong acid, HCl, and as such will not react with the surrounding water molecules. However, NH₄⁺ is the conjugate acid of the weak base ammonia. NH₃. As such it will react with water to form ammonia and the hydronium ion.

NH₄⁺ (aq) + H₂O (l) <--> NH₃(aq) + H₃O⁺ (aq)

Hydronium ions give the salt solution its acidic nature. "

My question is WHY do the Cl- ions not react with the surrounding water, But the NH₄⁺ ions do?

 

[rand_althor]

My question is WHY do the Cl- ions not react with the surrounding water, But the NH₄⁺ ions do?

HCl + H₂O -> Cl^- + H₃O⁺. HCl is a strong acid, meaning it ionises completely. Because of this, the reaction can't go the opposite direction.

NH₃ + H₂O <--> NH₄⁺ + OH^-. NH3 is a weak bsae, meaning it ionises partially. Because of this, the reaction can go either direction, allowing for the ammonium ions to react with water to form ammonia and hydronium ions.

 

[Drsoccerball]

First thing:

How come "acid + base --> salt + water" does not apply to HCl + NH₄ -->NH₄Cl

Because theres no oxygen in the equation therefore water cannot be made...

 

[someth1ng]

The acid+base thing is a really basic general rule referring to H+ and OH- which makes water and is only valid when in solution of water. It's more accurate to say that an acid is a proton donor and a base is a proton acceptor (water production isn't needed). In fact (beyond syllabus), acids are electron pair acceptors and bases are electron pair donors.

In your case, you make NH4OH in solution (when you have ammonia water) and when that reacts with HCl, you get water and NH4Cl. So in this context, NH4Cl is the salt and H2O is also produced.