Two pH questions i don't understand

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Discussion Overview

The discussion revolves around two questions related to pH calculations involving different solutions: comparing the pH of a 0.001 M NaOH solution with a 0.001 M Ba(OH)2 solution, and determining the pH of a 1.0 × 10-8 M HCl solution. The scope includes homework-related queries and conceptual understanding of pH and stoichiometry.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant claims that a 0.001 M solution of Ba(OH)2 has a higher pH than a 0.001 M solution of NaOH, but seeks clarification on how to determine this.
  • Another participant questions the nature of the 1.0 × 10-8 M solution, asking for confirmation that it is HCl, and expresses confusion over the pH calculation, suggesting that it should be less than 7.
  • There is a discussion about stoichiometry and its relevance to determining the number of moles of OH- in the solutions, with one participant suggesting that Ba(OH)2 would provide twice the number of moles compared to NaOH.
  • A later reply challenges the correctness of the pH calculation provided by the original poster, indicating uncertainty about the definitions and calculations involved.

Areas of Agreement / Disagreement

Participants express differing views on the pH of the HCl solution, with some suggesting it could be less than 7 while others question the calculations leading to that conclusion. The discussion remains unresolved regarding the correct interpretation of the pH values and the implications of stoichiometry in these contexts.

Contextual Notes

There are limitations regarding the assumptions made about the solutions and the definitions of pH being used. The discussion does not resolve the mathematical steps involved in determining the pH of the HCl solution.

AMan24
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Homework Statement


1) Which solution has the higher pH, a 0.001 M solution of NaOH or a 0.001 M solution of Ba(OH)2?

2) Would a 1.0 × 10-8M solution of HCl have pH < 7,
pH = 7, or pH > 7? My professor said she shouldn't have put HCl as the solution, but that it doesn't matter apparently.

Homework Equations



The Attempt at a Solution


1) answer is: A 0.001 M solution of Ba(OH)2 has the higher pH

2) answer is: pH < 7

My question:

For 1) How do i determine this? I have no idea how

For 2) I'm doing pH = -log[1.0 x 10-8] and I am getting pH = 8. How is the answer less than 7?
 
Last edited:
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AMan24 said:
1.0 × 10-8M solution
Of what?
AMan24 said:
How do i determine this? I have no idea how
Are you conversant with the concepts of stoichiometry?
 
Bystander said:
Of what?
Are you conversant with the concepts of stoichiometry?
It was HCl but she said it doesn't matter.

Yes i know stoichiometry
 
Please DO NOT edit. It makes it impossible to follow discussions.

And if the solute were a base? It matters.
What does stoichiometry tell you?
 
Bystander said:
Please DO NOT edit. It makes it impossible to follow discussions.

And if the solute were a base? It matters.
What does stoichiometry tell you?
I guess I could find the number of moles of OH in each of the molecules using molarity. And the Ba(OH)2 would have 2x the number of moles. If that's right then I could also figure it out if it were two different molarities.
 
Answer to 2 follows directly from definition of pH, and the one you give, I don't know whether it is yours or what you were told, seems wrong to me.

For 1 you are on the right lines; what do you think are the molarities of everything that is there in that Ba(OH)2 solution?
 
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