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Borek
science forum Guru Wannabe

Joined: 02 May 2005
Posts: 157

Posted: Sat Jul 01, 2006 8:16 am    Post subject: Re: pH Calculation

On Fri, 30 Jun 2006 23:14:35 +0200, omicron <info99@ptd.net> wrote:

 Quote: Concentrated HCL is 38.7% mass percentage and 12.1 molar (I believe that is accurate). Therefore, using arithmetic, if I dilute it (v/v) by taking 129 ml and bringing the final volume to 1000ml, I should have approximately a 5% solution. The math: 1000/129 = 7.75 38.7% / 7.75 = 4.99% or 5% Correct so far?

In the first post you have stated you HAVE 5% solution - why do you try to
dilute some other solution now? Just convert % to molarity, as described
here:

http://www.chembuddy.com/?left=concentration&right=percentage-to-molarity

 Quote: If so, then the molarity of the concentrated acid is also cut by the 7.75. The math here: 12.1 M / 7.75 = 1.56 M, so the molarity of a 5% HCL solution is approximately 1.56M. Also correct??

No, such approach will work only if the density of all solutions is
identical - it is not.

Best,
Borek
--
http://www.chembuddy.com
http://www.ph-meter.info/pH-measurements-indicators
http://www.terapia-kregoslupa.waw.pl
omicron1
science forum beginner

Joined: 30 Jun 2006
Posts: 2

Posted: Fri Jun 30, 2006 9:14 pm    Post subject: Re: pH Calculation

Hello Ricahrd,
Allow me to try your idea:
Concentrated HCL is 38.7% mass percentage and 12.1 molar (I believe
that is accurate).
Therefore, using arithmetic, if I dilute it (v/v) by taking 129 ml and
bringing the final volume to 1000ml, I should have approximately a 5%
solution. The math:
1000/129 = 7.75
38.7% / 7.75 = 4.99% or 5%
Correct so far?
If so, then the molarity of the concentrated acid is also cut by the
7.75. The math here:
12.1 M / 7.75 = 1.56 M, so the molarity of a 5% HCL solution is
approximately 1.56M.
Also correct??
Assuming your answer to both my questions is YES, I've completed the
first part of your roadmap answer to my original question.
Please let me know if I'm on the correct path and, if so, I'll then
tackle the 2 and 3 portion of your answer.
Thank you again!

Richard Schultz wrote:
 Quote: In article <1151638294.571462.58760@x69g2000cwx.googlegroups.com>, omicron wrote: : Can someone show me how to calculate the pH of a 5% Hydrochloric acid : solution? (1) What is the *molarity* of a 5% HCl solution? (2) Assuming that the HCl is completely dissociated, what is the concentration of H+ ions in a 5% HCl solution? (3) What is the relation between the H+ concentration of a solution and its pH? ----- Richard Schultz schultr@mail.biu.ac.il Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel Opinions expressed are mine alone, and not those of Bar-Ilan University ----- "an optimist is a guy/ that has never had/ much experience"
Borek
science forum Guru Wannabe

Joined: 02 May 2005
Posts: 157

Posted: Fri Jun 30, 2006 12:11 pm    Post subject: Re: pH Calculation

On Fri, 30 Jun 2006 05:31:34 +0200, omicron <info99@ptd.net> wrote:

 Quote: Can someone show me how to calculate the pH of a 5% Hydrochloric acid solution? I need to do it with no equipment or test papers. Any help would be greatly appreciated.
Richard Schultz
science forum Guru

Joined: 28 Apr 2005
Posts: 339

 Posted: Fri Jun 30, 2006 3:47 am    Post subject: Re: pH Calculation In article <1151638294.571462.58760@x69g2000cwx.googlegroups.com>, omicron wrote: : Can someone show me how to calculate the pH of a 5% Hydrochloric acid : solution? (1) What is the *molarity* of a 5% HCl solution? (2) Assuming that the HCl is completely dissociated, what is the concentration of H+ ions in a 5% HCl solution? (3) What is the relation between the H+ concentration of a solution and its pH? ----- Richard Schultz schultr@mail.biu.ac.il Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel Opinions expressed are mine alone, and not those of Bar-Ilan University ----- "an optimist is a guy/ that has never had/ much experience"
omicron1
science forum beginner

Joined: 30 Jun 2006
Posts: 2

 Posted: Fri Jun 30, 2006 3:31 am    Post subject: pH Calculation Can someone show me how to calculate the pH of a 5% Hydrochloric acid solution? I need to do it with no equipment or test papers. Any help would be greatly appreciated. Thank you.

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