Off Topic Chemistry Problem

[justin342]

I know this is off topic, but I didn't have anywhere else to turn for help and I know there are a lot of smart people in here.

Explain why a mixture of HCl and KCl does not function as a buffer, where as a mixture of HC(2)H(3)O(2) and NaC(2)H(3)O(2) does.

Anyone?

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[imtiaz]

HCl and KCl fully dissociate in solution, they are ionic compounds. Acetic acid and sodium acetate are covalent compounds which partially ionize and thus can become protonated/deprotonated as required to maintain pH (up to an extent).

HCl is a strong acid, acetic acid is a weak acid.

 

[justin342]

Sounds good. It seems obvious now that I read it. Thanks for the help.

 

[souljah1]

I'd like to add that HCl and KCl do not provide us with any base what soever. Acetic acid is a weak acid which can dissociate and associate based on its chemical structure (henderson hasselback or however you spell it).

 

[daisygirl]

Actually HCl and KCl do provide bases; the Cl- anions are considered lewis bases.

 

[souljah1]

the question i have is: will the pH go up if you add Cl-? I know that Cl- is a lewis base, but does Cl- have the capability of buffering??? it has no conjugate really.

 

[daisygirl]

•••quote:•••Originally posted by souljah1:
•the question i have is: will the pH go up if you add Cl-? I know that Cl- is a lewis base, but does Cl- have the capability of buffering??? it has no conjugate really.•••••You need a weak acid and its conjugate salt or a weak base and its conjugage salt in order to have a buffer solution. As imtiaz stated HCl and KCl will dissociate 100%, thus no buffer solution. The only reason I pointed out that Cl- is a lewis base is because there is a base present. In the question presented Cl- does not have the capability of buffering b/c it is not going to shift the equilibrium over to the left, thus the buffering effect. Adding more Cl- will increase the pH.

 

[mongoose]

Ultimately, there is no buffer effect because the Cl- anion is very stable and will not attack water or anything else to gain a proton. Well, there may be some things it will attack, but they would be few and far between, maybe I- anion but not to any great extent. To get a buffer, you must have something capable of attacking and removing protons from other species. Typically, this will involve an oxygen with a negative charge or a nitrogen with it's lone pair of electrons.