Idea Transcript
A website for Serious Education, promoting Aloha, & the most FUN Home
FAQs
you can have in metal finishing
Suggested Books
Help Wanteds
Advertise on this site
FORUM current topics
topic 53712
Determining pH of concentrated acetic acid
November 24, 2009 In my work, am dealing with highly concentrated acetic acid solution (90%).
I could not measure reducible pH value by the pH glass electrode. What I am sure about is that the pH is negative. Is there any suggested good way to know the pH of such solution? Regards Saud Al Subai - U.K.
First of two simultaneous responses -- November 26, 2009 pH is a logarithmic measure of the concentration of hydrogen ions in weak solutions, any attempt to measure the pH of an acetic acid solution at 90% is a waste of time. Brian Terry Aerospace - Yeovil, Somerset, UK
Second of two simultaneous responses -- November 26, 2009 Saud pH is a logorithmic scale and is practically meaningless at the extremes. pH lower than about 2 or higher than 12 require specialised electrodes and normally unavailable buffer standards. I am not convinced that negative pH is a viable concept. At high concentrations of acid or alkali, a simple titration is by far the easiest way to measure concentration. Geoff Smith Hampshire, England
December 2, 2009 Sir: Acetic acid is a "weak" organic acid with a dissociation constant of 1.76 x 10-5 at 25 C. A 90% (W/W) solution of acetic acid is 15.72 Molar. Using this information the calculated pH of the solution is 1.78. This would be a typical calculation problem for college freshmen chemistry students. In real-life this result has little application. Concentrated strong acids which are completely dissociated (which is the case) can have calculated pH's which are negative. Regards, Dr. Thomas H. Cook Galvanizing Consultant - Hot Springs, South Dakota
December 2, 2009 Let me try to summarize what has been said and add some to it. A cheap pH meter will be so far off that the results would be meaningless. A good pH meter can get accurate pH readings using the proper "buffers". 1 normal HCl has a pH of 1. pH buffers for 2 and 3 are available from scientific supply houses. Use of buffers has to span the range of the pH being measured as closely as possible. A 7 buffer is highly inappropriate, but is all that is available on many meters. Even with a good reading, pH is worthless for most (but not all) uses. This is because it is logarithmic so a very very tiny pH change is a massive change in concentration. Second, pH is only measuring free or disassociated acid and as you saw from a previous post, that amount is less than 1%, so it is a bad indicator of concentration. The good news is that a very simple and accurate titration can be performed by most people with an hour or so of training. James Watts - Navarre, Florida
This public forum has 60,000 threads. If you have a question in mind which seems off topic to this thread, you might prefer to Search the Site
ADD a Q or A to THIS thread
START a NEW THREAD
View CURRENT TOPICS
Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful. If you need a product/service, please check these Directories: Jobshops
Capital Equip. & Install'n
Chemicals & Consumables
Consult'g, Train'g, Software
Environmental Compliance
Testing Svcs. & Devices
©1995-2018 finishing.com, Inc., Pine Beach, NJ - About finishing.com - Privacy Policy How Google uses data when you visit this site.