INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

pH of 35.2 wt % HCl?

pH of 35.2 wt % HCl?

(OP)
Hi guys. Mech engr here, in over my head again, as usual. How do I estimate the pH of a 35.2 weight % HCl solution? Is this acid too strong to use the old pH = -log[H+] and I have to take the log of the activity (which I have no idea how to do)?

Thanks guys! Pete

RE: pH of 35.2 wt % HCl?

pH = -1.1

HCL

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: pH of 35.2 wt % HCl?

(OP)
Awesome. Thanks brother! Pete

RE: pH of 35.2 wt % HCl?

And, yes, it is too strong for the simple pH equation. pH is defined as 0 to 14. Notice it is -1.1.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

RE: pH of 35.2 wt % HCl?

(OP)
Right. That's why I was asking about the activity. Just from a quick Interpipes search, apparently for strong acids, a guy has to use pH=-log[a+] where a = activity of the hydrogen ion, I guess because strong acids do't completely dissociate. (ME in over his head again.) I have no idea how to find activity. It's not in my freshman chem textbook.

Source: http://antoine.frostburg.edu/chem/senese/101/acidb...


RE: pH of 35.2 wt % HCl?

Most manufacturers would list the pH as being 0 to 1 or <1. Information may be obtained from the material safety sheets.

http://www.cleartech.ca/ckfinder/userfiles/files/H...

Negative pH values may be possible, but would be unusual in practice. There are some complications in high molarity acid solutions that make pH calculations from acid molarity inaccurate and difficult to verify experimentally:

Even strong acids don't dissociate completely at high concentrations. Some of the hydrogen remains bound to the chlorine, making the pH higher than you'd expect from the acid molarity.

Because there are so few waters per acid formula unit, the influence of hydrogen ions in the solution is enhanced. We say that the effective concentration of hydrogen ions (or the activity) is much higher than the actual concentration. The usual general chemistry text definition of pH as -log [H+] (negative the logarithm of the hydrogen ion molarity) is better written as pH = - log aH+ (negative the logarithm of the hydrogen ion activity). This effect is very strong, and makes the pH much lower than you'd expect from the acid molarity.

If you were to dip a glass pH electrode into the 12 M HCl solution to actually measure the pH, you would get a pH that was higher than the true pH. This well-known defect in glass pH electrode measurements is called the "acid error"; it is sensitive to experimental conditions and difficult to correct for.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close