×
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!
  • Students Click Here

*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.

Students Click Here

Jobs

Neutralization calculators

Neutralization calculators

Neutralization calculators

(OP)
Hi there,

I have a 0.145 M solution of sulphuric acid.  I would like to adjust the pH of my solution to 3 through the addition of 50% sodium hydroxide (caustic soda) in order to precipate my iron impurities.  My knowledge of acid-base chemistry is extremely rusty.  Can anyone help me in determining how much sodium hydroxide will be required to make this pH adjustment?

RE: Neutralization calculators

What quantity of solution?

Have  [H+] =  0.290 N, since 2 H+ per mole sulfuric
For pH 3, want [H+] = 0.001 N,
so need to reduce sulfuric from 0.145 to 0.0005 M, i.e.,  neutralize 0.1445 M.  
Takes 2 NaOH to neutralize 1 mole of H2SO4.

So, desired reaction:  0.1445 moles sulfuric + 0.2890 moles sodium hydroxide = 0.1445 sodium sulfate + 0.2890 water

The FW of NaOH is 40, so need 80 grams of 50 wt% solution for 1 mole NaOH. The SG of 50 wt% NaOH solution is ~1.53 g/mL, so use about 15.1 mLs of 50 wt% NaOH per 1 L of 0.145 M sulphuric acid.

But, to be precise, the new total volume will be ~1.0151 L, which will slightly dilute the H+ below the desired 0.001 N.

Try adding (1000/1015.1) x 15.1 mLs = 14.875 mLs of the 50 wt% NaOH.

Actually, this was Just a preliminary calculation to get an idea of the quantities involve.  The  NaOH composition is more like 49-51 wt%, and probably don't know its exact SG.  So, you carefully add a smaller amount of NaOH while thoroughly stirring, and make final additions via pH.  Remember that pH is a log scale, so it will take smaller & smaller additions of NaOH to get the same ΔpH.  Also, unless the volume of sulfuric solution  is very large, you need to use more dilute NaOH to reach the desired pH precisely.  In titrating acids, usually use 1 N NaOH (~4 wt%), and final pH adustments are made dropwise (~0.05 mL).

RE: Neutralization calculators

(OP)
Thank you very much for your help!  We are using very large quanities of sulfuric solution (20,000L), so I suppose that means we can use more concentrated NaOH.  We have the specs for the 50% NaOH (sp. grav = 1.52, pH = 12).

Anything else we need to know?  

Thanks again, your help is much appreciated!

Sheena

RE: Neutralization calculators

Two comments.
1) A pH of 3 will only reduce [Fe+3] to 20 ppm.  Raising the pH to 4 will reduce it to 1 ppm.  See chart below



-- from http://www.finishing.com/Library/metalpH.html

2) Some 50% NaOH solution (technical grade) is quite high in salt, maybe 0.5% NaCl. If undesirable, ask supplier for analytics.

RE: Neutralization calculators

(OP)
I was hoping you could help me with another question.  I'm not entirely sure how you determined 15.1 mL of NaOH needed to be added using the specific gravity.  Is it possible for you to show me this calculation?

Thanks

RE: Neutralization calculators

(OP)
I figured it out!  You can ignore the last post.

Thanks,
Sheena

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