Why does the precipitate dissolve, reappear, and then dissolve again?

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In summary, when 5mL of 0.1 M silver nitrate solution is mixed with 5mL of 0.1 M HCl, a precipitate is formed. The addition of 6 M ammonium hydroxide solution causes the precipitate to dissolve, but when 10mL of 0.1 M HCl solution is added, the precipitate reappears. Finally, adding 5mL of 0.15 M sodium thiosulfate causes the precipitate to dissolve again. The repeated dissolving and reappearing of the precipitate is due to the solubility of AgCl being affected by the changing concentrations of the reactants.
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billabonger77
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why does the precipitate dissolve, reappear, and then dissolve again??

Homework Statement



i have a chem lab due tuesday and was wondering if anyone may please help me on it!

the problem:
Mix silver nitrate solution and hydrochloric acid solution. Product is a precipitate
2. Add ammonoum hydroxide solution drop by drop. precipitate dissolves.
3. Add hcl again. precipiate forms
4. add sodium thiosulfate..precipitate dissolves.

why does the precipitate dissolve, reappear, and then dissolve again??

Homework Equations





The Attempt at a Solution

 
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  • #2
1. AgNO3 + HCl -> HNO3 + AgCl
HNO3 is soluble, but AgCl isn't (see solubility rules), so it precipitates.

2. AgCl + NH4OH -> AgOH + NH4Cl
It dissolves? Really? :/

3. AgOH + HCl -> AgCl + H2O
AgCl is insoluble again, so it precipitates again.

4. 2AgCl + Na2S2O3 -> Ag2S2O3 + 2NaCl
Uhhh...

Well, at least you have the equations :P.
 
  • #3
hey how does the equations get affected when i use
1> 5mL of 0.1 M of silver nitrate solution mixed with 5mL of 0.1 M HCl.

2. then added 6 M ammoniumn hydroxide solution, drop by drop

3. then added 10 mL of 0.1 M HCl solution

4. then added 5mL of .15 M sodium thiosulfate
 

FAQ: Why does the precipitate dissolve, reappear, and then dissolve again?

Why does the precipitate form in the first place?

Precipitates form when two solutions with different ions are mixed together and a chemical reaction occurs. This reaction causes the formation of a solid substance, or precipitate, which is insoluble in the solution.

Why does the precipitate dissolve after appearing?

The precipitate dissolves because some of the ions in the solution react with the solid substance, breaking it down into smaller particles that are soluble. This process is known as dissolution.

What causes the precipitate to reappear after it has dissolved?

The precipitate reappears because the concentration of the dissolved ions in the solution increases as more of the solid substance dissolves. This increase in concentration can reach a point where the ions can no longer remain dissolved and they start to combine to form another precipitate.

Why does the precipitate dissolve again after reappearing?

The precipitate dissolves again because the concentration of the dissolved ions continues to increase, causing the solution to become saturated. When a solution is saturated, it cannot hold any more solute and any excess solid will dissolve.

Is the appearance and disappearance of the precipitate a reversible process?

Yes, the precipitation-dissolution cycle is a reversible process. It depends on the concentration of the dissolved ions and can occur multiple times as the solution becomes saturated and then diluted again. This process can continue until either all of the solid substance has dissolved or the concentration of the dissolved ions reaches an equilibrium point.

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