Chem question help (1 Viewer)

[MyHeadee]

Answers say D, i dont understand how. Wouldnt the original addition of Silver Nitrate (in excess), cause the less soluble AgCl to precipitate, and then cause AgOH to also precipitate out?

 

[dasfas]

This is a poorly posed question and you're absolutely right to be confused.

Using this table, Ksp whereas Ksp

So just by using the Ksp, we could infere that Cl- will be precipitated out first. Since the flow chart doesn't demonstrate the production of 2 precipitates due to the addition of AgNO3, we can safely assume precipitate 1 is AgCl. We also have to assume that exactly the right amount of AgNO3 was added, such that no AgOH precipitated.

Then, we add Ca2+. We know all sulfates are soluble except for Ca2+, Ba2+ and Pb2+. Thus this must be CaSO4. We confirm this using the fact that all hydroxides are insoluble, except for Rule 2, lead and Ca (slightly).

So precipitate 2 is CaSO4, filtrate 2 is a hydroxide solution.

So the answer is C

For reference, the solubility rules:

1) All nitrates and acetates are soluble

2) All Group 1 and ammonium salts are soluble

3) All chlorides, bromides, iodides are soluble except for silver and lead

4) All sulfates are soluble except barium, lead, calcium

5) All hydroxides are insoluble except for Rule 2, barium and calcium (slightly)

6) All carbonates are insoluble except Rule 2

 

[bigwilly69]

This is a poorly posed question and you're absolutely right to be confused.

Using Ksp whereas Ksp

So just by using the Ksp, we could infere that Cl- will be precipitated out first. Since the flow chart doesn't demonstrate the production of 2 precipitates due to the addition of AgNO3, we can safely assume precipitate 1 is AgCl. We also have to assume that exactly the right amount of AgNO3 was added, such that no AgOH precipitated.

Then, we add Ca2+. We know all sulfates are soluble except for Ca2+, Ba2+ and Pb2+. Thus this must be CaSO4. We confirm this using the fact that all hydroxides are insoluble, except for Rule 2, lead and Ca (slightly).

So precipitate 2 is CaSO4, filtrate 2 is a hydroxide solution.

So the answer is C

For reference, the solubility rules:

1) All nitrates and acetates are soluble

2) All Group 1 and ammonium salts are soluble

3) All chlorides, bromides, iodides are soluble except for silver and lead

4) All sulfates are soluble except barium, lead, calcium

5) All hydroxides are insoluble except for Rule 2, barium and calcium (slightly)

6) All carbonates are insoluble except Rule 2

I got C too but the answers say D :/

 

[dasfas]

I got C too but the answers say D :/

I just checked the molar solubility of Ca(OH)2 using the table linked and got 0.0125M, whereas the molar solubility of CaSO4 = 0.00490M. So clearly CaSO4 is less soluble than Ca(OH)2.

I believe the answers are incorrect - CaSO4 would precipitate, not Ca(OH)2.

However, perhaps I am incorrect and someone has a plausible explanation for why it is D, but I'm not seeing it.

 

[MyHeadee]

I just checked the molar solubility of Ca(OH)2 using the table linked and got 0.0125M, whereas the molar solubility of CaSO4 = 0.00490M. So clearly CaSO4 is less soluble than Ca(OH)2.

I believe the answers are incorrect - CaSO4 would precipitate, not Ca(OH)2.

However, perhaps I am incorrect and someone has a plausible explanation for why it is D, but I'm not seeing it.

Thank you very much

 

[bigwilly69]

I just checked the molar solubility of Ca(OH)2 using the table linked and got 0.0125M, whereas the molar solubility of CaSO4 = 0.00490M. So clearly CaSO4 is less soluble than Ca(OH)2.

I believe the answers are incorrect - CaSO4 would precipitate, not Ca(OH)2.

However, perhaps I am incorrect and someone has a plausible explanation for why it is D, but I'm not seeing it.

A gentleman and a scholar, thank you