An aqueous solution containing 0.0020 mol/L barium hydroxide, what is the pH? I do the following: 14-(-log(0.0020))=11.3pH. The answer is 11.6.

2.0*10^-3 mol/L sodium hydroxide solution, what is the pH? I do the following: 14-(-log(0.002))=11.3pH. The answer is 9.3

When I solve for pH of solutions with acidic solutes, I get the accurate answer, such as in the question: 2.0*10^3 mol/L nitric acid solution, where I do: -log(0.002)=2.7pH, which matches the answer, 2.7.

My question is, why am I getting the discrepancy between the calculated and the given answer when calculating pH for solutions with base solute? Or am I not doing anything wrong?


Because barium hydroxide is $\ce{Ba(OH)2}$

The book is assuming each mole of barium hydroxide release 2 moles of hydroxide ions, while you are assuming only 1 mole is released.

  • $\begingroup$ Please disambiguate. $\endgroup$ – Arthur Alex Karapetov Jun 2 '16 at 22:21
  • $\begingroup$ @ArthurAlexKarapetov OK, I added to the answer. $\endgroup$ – DavePhD Jun 2 '16 at 22:40
  • $\begingroup$ I see. But what about sodium hydroxide (NaOH)? There is only 1 hydroxide ion released there. In my question, it doesn't work out either. Please help understand why? $\endgroup$ – Arthur Alex Karapetov Jun 2 '16 at 22:45
  • $\begingroup$ Your answer is right for 0.002M NaOH $\endgroup$ – DavePhD Jun 2 '16 at 22:49

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.