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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Shadow on December 16, 2014, 01:43:23 PM

Title: Is ammonium acetate a buffer?
Post by: Shadow on December 16, 2014, 01:43:23 PM: Is ammonium acetate solution a buffer? I think it is even if there are species which aren't conjugated.
Title: Re: Is ammonium acetate a buffer?
Post by: mjc123 on December 17, 2014, 05:01:51 AM: What has conjugation got to do with it?
Title: Re: Is ammonium acetate a buffer?
Post by: Borek on December 17, 2014, 05:36:26 AM: I think he refers to the lack of an acid and a conjugate base pair.

No, it is not a buffer, even it has some properties of one. Can you list what are typical buffer properties, and predict, which of them ammonium acetate solution has?
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 19, 2014, 12:11:25 PM: Concentration ratio of the acid and base shouldn't be bigger than 10:1, the acid and base should be weak. I can't think of more.
Title: Re: Is ammonium acetate a buffer?
Post by: Borek on December 19, 2014, 01:24:59 PM: How does the buffer behave?
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 20, 2014, 03:50:32 AM: The acid reacts with OH- from added base, and the base reacts with H+ from the added acid.
Title: Re: Is ammonium acetate a buffer?
Post by: Borek on December 20, 2014, 04:57:30 AM: No, I mean - how does the pH change when adding base/acid, how does the pH change on dilution? These are the reasons we use buffers, so its the most important and the most basic characteristics, isn't it?
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 20, 2014, 07:30:06 AM: It changes a little.
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 20, 2014, 12:10:58 PM: Can I get the answer to my question now?
Title: Re: Is ammonium acetate a buffer?
Post by: billnotgatez on December 20, 2014, 12:13:28 PM: I am curious
have you done any titration curves we could see
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 20, 2014, 12:20:42 PM: No, but I am curious how it would look like.
Title: Re: Is ammonium acetate a buffer?
Post by: Babcock_Hall on December 20, 2014, 03:06:45 PM: http://www.tutorvista.com/content/chemistry/chemistry-iii/ionic-equilibrium/titrations-acid-base.php

What does the bottom titration curve suggest about its ability to resist changes in pH?
Title: Re: Is ammonium acetate a buffer?
Post by: Borek on December 20, 2014, 03:52:06 PM: Quote from: Shadow on December 20, 2014, 12:10:58 PM
Can I get the answer to my question now?

Can you start thinking on your own please? As you have stated buffer pH changes only a little bit in response to acid/base added. What happens to the pH of the ammonium acetate solution?
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 21, 2014, 03:33:48 AM: It changes a little. So it should be buffer!
Title: Re: Is ammonium acetate a buffer?
Post by: Borek on December 21, 2014, 06:42:27 AM: Quote from: Shadow on December 21, 2014, 03:33:48 AM
It changes a little.

How much is "a little"? Show numbers. Say, you have 100 mL of 0.1 M acetate buffer at pH 4.75 and you add 1 mL of 1 M HCl solution. Then, you have 100 mL of 0.1 M ammonium acetate at pH 7.00 and you add 1 mL of 1 M HCl solution. By how much does pH change in each case?
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 21, 2014, 07:26:27 AM: It depends on the capcity of the buffer, but I don't know how to use it.
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 21, 2014, 08:02:21 AM: The second system is complex equilibria.
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 21, 2014, 09:02:40 AM: I got that the pH will change to ca. 3.4 for both buffers, meaning that their capacity will be broken.
Title: Re: Is ammonium acetate a buffer?
Post by: Borek on December 21, 2014, 12:44:43 PM: I am afraid 3.4 is not correct for neither solution. Show how you got it.

Second problem is not that difficult. What is the initial pH of the ammonium acetate solution? What can you tell about ammonia at this pH? How much is protonated? Is there enough NH₃ to react with the added acid? If not - what does the added acid react with?
Title: Re: Is ammonium acetate a buffer?
Post by: Shadow on December 21, 2014, 01:05:03 PM: 7, ammonia is protonated, acetate reacts with protons in both cases.
Title: Re: Is ammonium acetate a buffer?
Post by: Borek on December 21, 2014, 02:00:53 PM: Which is a good starting point to calculate the new pH.
Title: Re: Is ammonium acetate a buffer?
Post by: Archy12345 on December 28, 2014, 02:10:10 AM: I wish I had a pH meter accurate enough to do a decent calibration curve, because I'm very interested to see how this solution would react.

I think that it could have some pH change resisting qualities, but as far as it meeting the criteria for the definition of a buffer, no it's not a buffer.