ERROR FIXED: A technical question I made up

[shaq786]

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Wait a minute...I MADE AN ERROR IN STATING THE QUESTION...sorry. Let me restate it...

Lets say you have a weak acid(Acetic acid) and its weakly dissolved in water. So there are insoluble acetic acid chunks in the solution. Now lets say you add more water and dissolve all of acetic acid. What happens to the pH????? Would it decrease becuase H+ is dissassociated completely in the solution or would the increase in water concentration cause a dilution in pH from what it was in the very beginning????????????

 

[chopper]

acetic acid is itself soluble in water (small, polar molecule) without dissociating. I dont' think there are any 'chunks'.

 

[murphomatic]

It's both

increase in pH = decrease in H+ ion concentration

so as you add more water more acid dissociates, but not enough to compensate for the increasing concentration of water.

 

[Fenotypic]

It's both

increase in pH = decrease in H+ ion concentration

so as you add more water more acid dissociates, but not enough to compensate for the increasing concentration of water.

I would assume that the pH remains fairly stable up to a point. Based on LeChateleir's (sp?) principle (and pKa values) the more water you add, the more acid dissociates and therefore your overall concentration of H+ remains fairly constant ( your new equilibrium would contain H+ and water in the same ratio as the original solution) ---- untill you have dissociated all the acid, to which adding more water would make the pH increase.

 

[MDtoBe777]

Wait a minute....if you dilute the solution the molarity will decrease, right? THerefore, the concentration of H+ overall would decrease too. So, the pH would increase? So if you dilute the acid, then pH does increase. Right?

 

[Medikit]

The pH would stay the same

 

[shaq786]

Wait a minute...I MADE AN ERROR IN STATING THE QUESTION...sorry. Let me restate it...

Lets say you have a weak acid(Acetic acid) and its weakly dissolved in water. So there are insoluble acetic acid chunks in the solution. Now lets say you add more water and dissolve all of acetic acid. What happens to the pH????? Would it decrease becuase H+ is dissassociated in the solution or would the increase in water concentration cause a dilution in pH from what it was in the very beginning????????????

 

[Medikit]

Wait a minute...I MADE AN ERROR IN STATING THE QUESTION...sorry. Let me restate it...

Lets say you have a weak acid(Acetic acid) and its weakly dissolved in water. So there are insoluble acetic acid chunks in the solution. Now lets say you add more water and dissolve all of acetic acid. What happens to the pH????? Would it decrease becuase H+ is dissassociated in the solution or would the increase in water concentration cause a dilution in pH from what it was in the very beginning????????????

It would stay the same because the concentration of acetate dissolved in solution would stay the same since for there to be undissolved acetate the water must be saturated. Adding more water will simply dissolve some of the undissolved acetate and leave the solution saturated. Overall more protons have become dissociated, but the concentration has not changed.

 

[shaq786]

thanks medkit...that makes sense

 

[BisMuOxo]

This example doesn't make sense. Acetic acid is a LIQUID at room temperature and it is miscible with water......there cannot be any undissolved chunks.