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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=percentagetomolarity
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.phmeter.info/pHmeasurementsindicators
http://www.terapiakregoslupa.waw.pl 

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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,
Thank you for your reply.
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 <info99@ptd.net> 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, BarIlan University, RamatGan, Israel
Opinions expressed are mine alone, and not those of BarIlan University

"an optimist is a guy/ that has never had/ much experience" 


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Borek science forum Guru Wannabe
Joined: 02 May 2005
Posts: 157


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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 <info99@ptd.net> 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, BarIlan University, RamatGan, Israel
Opinions expressed are mine alone, and not those of BarIlan University

"an optimist is a guy/ that has never had/ much experience" 

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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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