Number of HCl Equivalents in 100mL of pH 4 Solution

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Discussion Overview

The discussion revolves around calculating the number of equivalents of HCl in a 100 mL solution with a pH of 4. Participants explore the relationship between pH, H+ concentration, and the concept of equivalents in acid-base reactions.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • One participant calculates the concentration of H+ ions to be 10^-4 M based on the pH and expresses confusion about the concept of equivalents in the absence of a clear acid-base reaction.
  • Another participant emphasizes the need to convert the volume of the solution to liters to compute the number of moles and assumes complete ionization of HCl in solution.
  • Multiple participants assert that the number of moles of HCl corresponds to 10^-5 moles, with some questioning the necessity of considering water as a base in the reaction.
  • There is a discussion about the complete ionization of HCl and its relevance to calculating H+, with one participant noting that dissociation is generally irrelevant when calculating equivalents for weak acids.
  • One participant confirms that HCl will ionize completely, allowing for the calculation of H+ concentration.

Areas of Agreement / Disagreement

Participants generally agree on the complete ionization of HCl and the calculation of H+ concentration, but there is some uncertainty regarding the conceptual framework of equivalents and the role of dissociation in different types of acids.

Contextual Notes

Participants mention the importance of complete ionization for HCl but also note that this may not apply to weak acids, indicating a potential limitation in the generalization of the concept of equivalents.

Hydrous Caperilla
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Homework Statement



Number of equivalents of HCL present in 100 ml of it's solution whose PH is 4

Homework Equations



PH= -Log[H+][/B]

The Attempt at a Solution



I used the above equation to find the concenteration of H+ and found it to be 10^-4 M.I am stuck after that. I searched the wiki and found a equivalent to be a substance which releases 1 mol of H+ in acid-base reaction but I don't find an acid base reaction here?[/B]
 
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You need the volume of the solution in liters. If you know the molarity, (and yes, you calculated it correctly), how do you compute the number of moles? ## \\ ## HCl is assumed to ionize completely in solution. Likewise when mixed with a base, the HCl is assumed to react with 100% efficiency.
 
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Number of moles of HCl in the solution is then 10^-5 moles.

Do I have to assume to consider HCL as acid and water as base and proceed with this reaction

HCL(aq)-------->H+(aq)+Cl-(aq)
 
Hydrous Caperilla said:
Number of moles of HCl in the solution is then 10^-5 moles.

Do I have to assume to consider HCL as acid and water as base and proceed with this reaction

HCL(aq)-------->H+(aq)+Cl-(aq)
Not necessary, and that would really be incorrect (to assume it is reacting with water). What you are computing is the number of moles of ## H^+ ##, also called "equivalents" that are available to react with a basic (meaning "base") solution, such as NaOH. ##\\ ## And you computed it correctly. ## \\ ## (Such a reaction would neutralize the NaOH with the result being a NaCl (salt) solution which is neutral (neither acidic or basic). The ## OH^- ## would react with ## H ^+ ## to form ## H_2 O ## which is of course water).
 
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So regardless of the base,HCL will ionise completely and so we can calculate H+ ...right?
 
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Hydrous Caperilla said:
So regardless of the base,HCL will ionise completely and so we can calculate H+ ...right?
That is correct.
 
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Thanx for the help
 
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Hydrous Caperilla said:
So regardless of the base,HCL will ionise completely and so we can calculate H+ ...right?

When calculating number of equivalents dissociation is irrelevant in general. For a weak acid - like acetic - number of equivalents means "amount of H+ that can react" - not necessarily "dissociated".

In the case of your question 100% dissociation was an important factor in determining HCl concentration, other than that it didn't matter.
 
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A fair point
 

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