common ion effect

[ihearindiemusic]

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Hi,

I am working on the passage. Question asks how we can make more CaCo3

one of the wrong answer choices is: adding a salt, cacl2, to the water. The explanation says that adding the common ion will decrease CaCO3 solubility in groundwater by common ion effect.

here is the reaction mentioned in the passage:

caco3 + h3o+ -> ca2+ + hco3- + h2o

Doesn't that mean that more CaCO3 solid will be created? I am really confused as to why adding CaCl2 to would not repair the loss of CaCO3.

I've been having problems with common ion questions like this - it's either I wrongly interpret what the question is asking about (more/less CaCO3) or I am not applying the common ion effect right.

Thank you! 🙂

 

[Temperature101]

Hi,

I am working on the passage at the end of the Equilibrium Chapter in the Princeton Review book. Questions 6 on for the passage, one of the wrong answer choices is: adding a salt, cacl2, to ground water. The explanation says that adding the common ion will decrease CaCO3 solubility in groundwater by common ion effect. here is the reaction mentioned in the passage:

caco3 + h3o+ -> ca2+ + hco3- + h2o

Doesn't that mean that more CaCO3 solid will be created? The question asks how you can create more stalagmite, which from my understanding happens by making more calcium carbonate. I am really confused as to why adding CaCl2 to ground water would not repair the stalagmite damage in the cave. I've been having problems with common ion questions like this - it's either I wrongly interpret what the question is asking about (more/less CaCO3) or I am not applying the common ion effect right.

Thank you! 🙂

CaCl2 will dissociate to Ca++ and 2Cl-. Adding more calcium ions to a solution that has CaCO3 will make the equilibrium shift to the left , which will create more calcium carbonate. This is the essence of the common ion effect.

 

[Temperature101]

Hi,

I am working on the passage. Question asks how we can make more CaCo3

one of the wrong answer choices is: adding a salt, cacl2, to the water. The explanation says that adding the common ion will decrease CaCO3 solubility in groundwater by common ion effect.

here is the reaction mentioned in the passage:

caco3 + h3o+ -> ca2+ + hco3- + h2o

Doesn't that mean that more CaCO3 solid will be created? I am really confused as to why adding CaCl2 to would not repair the loss of CaCO3.

I've been having problems with common ion questions like this - it's either I wrongly interpret what the question is asking about (more/less CaCO3) or I am not applying the common ion effect right.

Thank you! 🙂

You answer your own question...If more CaCO3 will be created; therefore, CaCO3 solubility decreases. Less of it will be dissociated.

 

[ihearindiemusic]

That's what I thought too but that answer choice is marked wrong. The right answer choice is adding a chemical compound that absorbs CO2 from the air which after like 3 reactions results in CaCO3 formation....I still don't understand why decreasing CaCO3 solubility through this common ion effect would not correct for the damage in the cave...don't we want more CaCO3 to repair the damage? Or is this a mistake in the book?....

 

[Temperature101]

That's what I thought too but that answer choice is marked wrong. The right answer choice is adding a chemical compound that absorbs CO2 from the air which after like 3 reactions results in CaCO3 formation....I still don't understand why decreasing CaCO3 solubility through this common ion effect would not correct for the damage in the cave...don't we want more CaCO3 to repair the damage? Or is this a mistake in the book?....

Dont know the context of the question... I would have to look at the passage

 

[Proof]

I think using the common ion effect will shift the reaction to the initial CaCO3 concentration. If you consider the initial amount, you are not adding more to this. The other reaction is actually making more CaCO3.