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Author Topic: Help on Writing Equation!  (Read 8796 times)

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starie

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Help on Writing Equation!
« on: March 26, 2010, 09:45:36 PM »

Hey guys

Would appreciate if anybody could help me with the following:

  • Chemical equation for Tris Buffer (Tris HCl/Tris Base)?
  • What is the final conc of the buffer (Tris HCl/Tris Base pKa 8.1, Buffer of ionic strength 0.05M, pH 8.5)

Thanks in advance!
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starie

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Re: Help on Writing Equation!
« Reply #1 on: March 26, 2010, 10:18:00 PM »

Oh man.  :( Anybody?  ???
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Matias Ekstrand

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Re: Help on Writing Equation!
« Reply #2 on: March 26, 2010, 11:18:26 PM »

I'd recommend that you let a bit more time pass than 30 minutes before you *Ignore me, I am impatient* up your thread.
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starie

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Re: Help on Writing Equation!
« Reply #3 on: March 26, 2010, 11:28:16 PM »

Oh opps. Ok thanks :]
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Borek

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Re: Help on Writing Equation!
« Reply #4 on: March 26, 2010, 11:36:14 PM »

Would appreciate if anybody could help me with the following:

Please read forum rules.

Quote
Chemical equation for Tris Buffer (Tris HCl/Tris Base)?

No such thing as "chemical equation" for Tris buffer. Perhaphs you mean Henderson-Hasselbalch equation? But I would not call it "chemical".

Quote
]What is the final conc of the buffer (Tris HCl/Tris Base pKa 8.1, Buffer of ionic strength 0.05M, pH 8.5)

How old is my daughter?

If you don't get it: you have about as much information about my daughter as we have about your problem. Can you answer my question? No. Can we even think about answering your question? No.

To make things worse I have only a son.
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starie

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Re: Help on Writing Equation!
« Reply #5 on: March 27, 2010, 12:01:17 AM »

Hi

Ok I am very sorry about it. I had missed out on that and I will rephrase my question.
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starie

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Re: Help on Writing Equation!
« Reply #6 on: March 27, 2010, 12:35:33 AM »

**MODIFIED**

To write the Henderson-Hasselbalch equation for Tris Buffer.

And my answer:
Tris·HCl + H2O ↔ Tris·Cl + + H3O+

My question is
Did I get that right? But somehow I am wondering if it is supposed to be TrisClˉ for the conjugate base instead.

Secondly,
Is there any molecular formula for Tris·HCl & Tris·Cl?
I have searched on Wikipedia and it is actually C4H11NO3 for Tris. So is it actually C4H11NO3HCl for Tris·HCl and C4H11NO3Cl for Tris·Cl?

*************

As for the second question.

Find the total concentration of a buffer of 100mL with the ionic strength of 0.05M.

I have actually worked this out using the formula n = cV
∴ c = n/V
c = 0.05M/0.1L
   = 0.5mol

Did I get the right formula? I am quite confused with the whole molarity thing and am trying to fix up the pieces of the different formulas that I can actually use.

*********************

Thanks for your help :]




Hey guys

Would appreciate if anybody could help me with the following:

  • Chemical equation for Tris Buffer (Tris HCl/Tris Base)?
  • What is the final conc of the buffer (Tris HCl/Tris Base pKa 8.1, Buffer of ionic strength 0.05M, pH 8.5)

Thanks in advance!
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Borek

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Re: Help on Writing Equation!
« Reply #7 on: March 27, 2010, 04:17:39 AM »

**MODIFIED**

To write the Henderson-Hasselbalch equation for Tris Buffer.

And my answer:
Tris·HCl + H2O ↔ Tris·Cl + + H3O+

You are completely clueless, aren't you?

I have even no idea where to start.

Hendenrson-Hasselbalch equation allows calculation of pH, what you are trying to write is a reaction equation of dissociation of protonated TRIS.
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starie

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Re: Help on Writing Equation!
« Reply #8 on: March 27, 2010, 04:47:11 AM »

Yup indeed I am really very confused.

****************************

I understand that the HH Equation is actually:
pH = pKa + log [base]/[acid]

which is why I have gotten all mixed up. Trying to get back on track.

****************************

I have done a similar question and this is the question:

Write out the chemical equation for phosphate buffer. Identify which species is the conjugate acid and conjugate base.

My answer:

H2PO4ˉ      + H2O  ↔   HPO4          + H3O+
(conjúgate acid)                  (conjugate base)


I have checked with my lecturer and it was done right.

*********************

The problem now is I am rather confuse with the Tris molecular formula and what has been dissociated.

The actual question is actually this:
Write the chemical equation for this buffer.

They actually had the word chemical equation. So does that mean that I have to write what has been dissociated?

If I am looking to write the dissociation, will that be right?

Tris·HCl + H2O ↔ Tris·Cl + + H3O+

Sorry if I have got you all confused too.
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starie

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Re: Help on Writing Equation!
« Reply #9 on: March 27, 2010, 05:07:27 AM »

Hey guys

My lecturer has gotten back to me. Just in case anyone is wondering, for the dissociation it would be:

TrisHCl (conjugate acid)  ↔   TrisClˉ (conjugate base)  + H+
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Borek

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Re: Help on Writing Equation!
« Reply #10 on: March 27, 2010, 05:47:51 AM »

Write out the chemical equation for phosphate buffer.

Is that really what your lecturer asked? As far as I can tell there is no such thing as "chemical equation". There is a "reaction equation". But even then, there is no such thing as "equation for buffer", there is equation of dissociation reaction.

My lecturer has gotten back to me. Just in case anyone is wondering, for the dissociation it would be:

TrisHCl (conjugate acid)  ↔   TrisClˉ (conjugate base)  + H+

Seems like your lecturer is as clueless as you are. There is no such thing as TrisCl-.

Tris is a weak base. Tris.HCl is called Tris hydrochloride, and is a salt. This salt, when dissolved, dissociates to protonated Tris (TrisH+) and Cl-. THEN protonated Tris can dissociate further:

TrisH+ <-> Tris + H+

these are your acid and conjugate base.
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