Number of HCl Equivalents in 100mL of pH 4 Solution

[Hydrous Caperilla]

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]

 

[Charles Link]

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.

 

[Hydrous Caperilla]

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)

 

[Charles Link]

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).

 

[Hydrous Caperilla]

So regardless of the base,HCL will ionise completely and so we can calculate H+ ...right?

 

[Charles Link]

So regardless of the base,HCL will ionise completely and so we can calculate H+ ...right?

That is correct.

 

[Hydrous Caperilla]

Thanx for the help

 

[Borek]

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.

 

[Hydrous Caperilla]

A fair point