Calculate the pH of concentrated hydrochloric acid

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Discussion Overview

The discussion revolves around calculating the pH of concentrated hydrochloric acid, specifically a solution that is 24.8% HCl by weight with a density of 1.16 g/mL. Participants explore the implications of the percentage concentration and the appropriate method for calculating pH in such concentrated solutions.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on the meaning of "percent by weight" in the context of the problem.
  • Another participant suggests that "percent by weight" could be interpreted as "percent by mass," leading to a calculation of the mass of HCl in the solution.
  • A third participant calculates the number of moles of HCl and derives a molar concentration, concluding with a pH value of -0.897.
  • A later reply acknowledges the effort but indicates that calculating pH in such concentrated solutions may not be valid using standard methods.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the validity of the pH calculation method for concentrated solutions. There is acknowledgment of the effort made, but also a challenge to the appropriateness of the approach used.

Contextual Notes

Participants note that the standard method for calculating pH may not apply to concentrated solutions, highlighting potential limitations in the approach taken.

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Homework Statement



Calculate the pH of concentrated hydrochloric acid if this solution is 24.8 % HCl by weight and has a density of 1.16 g/mL.

Homework Equations





The Attempt at a Solution


\the percentage is throwing me of, can someone explain what it is?
 
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I'm wildly guessing here, but if "percent by weight" somehow is supposed to mean "percent by mass," it would make things pretty easy; in 1.16g/mL, 28% of 1.16g would be HCl: (1.16g/mL)(0.28) = 0.3248g/mL.

From there, you can do some converting to eventually get to pH; I'll assume for now that only the percentage was tripping you up.
 


hey, useing what u told me i think i mite be getting somewhere:

n HCl = (0.248)*(1.16g)/(36.453g/mole) = 0.0789 moles

The molar concentration is thus [HCl] = (0.00789 moles)/(0.001 lit)

= 7.89M = [H+]

pH = -log([H+]) = -0.897

can someone verify?
 


Yes and no. Yes - you did your best and that's probably what your teacher wants. No - in such concentrated solutions pH can't be calculated this way. But that's not your fault and you can't do anything about it.
 

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