when ammonia is added to Zn(NO3)2 solution, a white precipitate forms, which dissolves on the addition of excess ammonia. But when ammonia is added to a mixture of Zn(NO3)2 and NH4NO3, no precipitate forms at any time. Suggest an explanation for this difference in behaviour.

1. NH3 + H2O ==> NH4^+ + OH^-

2. Zn + 2OH^- ==> Zn(OH)2
3. Zn(OH)2 + NH3 ==> Zn(NH3)4^+2 + 2OH^-
4. Ksp = (Zn^+)(OH^-)^2
5. NH4Cl ==> NH4^+ + Cl^-

NH3 produces OH^- (eqn 1) which combines with Zn (eqn 2) to form Zn(OH)2, a white ppt. An excess of NH3 gives eqn 3 in which the white ppt of Zn(OH)2 dissolves because of the formation of the Znb(NH3)4^+2 ion.

The fun starts by adding NH4Cl to the NH3 solution. Everything after that goes because of Le Chatelier's Principle. Here we go. Addition of NH4Cl increases the NH4^+ so much it forces the equilibrium of equation 1 to the left. That decreases the OH^- so much that the Ksp for Zn(OH)2 can not be exceeded which prevents the pptn of Zn(OH)2 so no white ppt forms first when NH3 is added.

thanks!

This is due to the buffer solution occurred

Ah, the good old ammonia and its quirky behavior, never fails to keep us entertained! So, here's the deal: when you add ammonia to a Zn(NO3)2 solution, a white precipitate forms. But, when you introduce the mischievous NH4NO3 into the mix, no precipitate is formed. What's going on here?

Well, let me enlighten you with some science circus tricks! The secret lies in the presence of ammonium ions (NH4+) from NH4NO3. These little troublemakers snatch away the party hats from the zinc ions (Zn2+) and create a complex called [Zn(NH3)4]2+. Yeah, I know, chemistry's got quite the fancy secret language!

This complex, with its ammonia buddies, remains in solution instead of forming a precipitate. Sneaky, right? So, it seems that the ammonium ions are the ultimate party crashers for our Zn(NO3)2 and ammonia precipitate.

In simpler terms, the addition of NH4NO3 provides extra ammonia molecules, creating a cozy environment where zinc ions don't feel the need to solidify into a precipitate. They're too busy hanging out with their ammonia friends to bother forming a precipitate.

Remember, chemistry can be a bit of a clown sometimes, but understanding its tricks will ensure you're never left scratching your head in confusion!

The difference in behavior observed when adding ammonia to a solution of Zn(NO3)2 versus a mixture of Zn(NO3)2 and NH4NO3 can be explained by the formation of complex ions.

When ammonia (NH3) is added to a solution of Zn(NO3)2, a white precipitate of Zn(OH)2 forms initially. This is because the ammonia reacts with zinc ions (Zn2+) present in the solution to form a hydroxide complex, known as Zn(OH)2. The chemical equation for this reaction can be written as follows:

Zn(NO3)2(aq) + 2NH3(aq) + 2H2O(l) → Zn(OH)2(s) + 2NH4NO3(aq)

However, the precipitate formed is not stable and redissolves on the addition of excess ammonia. The excess ammonia molecules coordinate with the Zn(OH)2 precipitate, forming the soluble complex ion known as tetraamminezinc(II), [Zn(NH3)4]2+. The chemical equation for this reaction can be written as follows:

Zn(OH)2(s) + 4NH3(aq) → [Zn(NH3)4]2+(aq) + 2H2O(l)

On the other hand, when ammonia is added to a mixture of Zn(NO3)2 and NH4NO3, no precipitate forms at any time. This is because the presence of ammonium ions (NH4+) from NH4NO3 affects the formation of the Zn(OH)2 precipitate. The ammonium ions can also form complex ions with ammonia, competing with the formation of Zn(OH)2. The ammonium ions, being common to both Zn(NO3)2 and NH4NO3, occupy the ammonia molecules, preventing them from reacting with zinc ions to form the precipitate. So, no white precipitate forms.

The difference in behavior arises due to the influence of the ammonium ions on the formation of the Zn(OH)2 precipitate and the subsequent complexation with ammonia.