What is the pH of a .001 M solution of HCl?

1 Answer
Stefan V.
Jan 8, 2016

#"pH" = 3#

Explanation:

Hydrochloric acid, #"HCl"#, is a strong acid, which means that it dissociates completely in aqueous solution to form hydronium ions, #"H"_3"O"^(+)#, and chloride anions, #"Cl"^(-)#, in a #1:1# mole ratio.

This tells you that every mole of hydrochloric acid will dissociate to produce one mole of hydronium ions and one mole of chloride anions in aqueous solution.

http://wps.prenhall.com/wps/media/objects/476/488316/ch14.html

The balanced chemical equation looks like this

#"HCl"_text((aq]) + "H"_2"O"_text((l]) -> "H"_3"O"_text((aq])^(+) + "Cl"_text((aq])^(-)#

As you know, the pH of a solution is simply a measure of the concentration of hydronium ions.

#color(blue)("pH" = - log(["H"_3"O"^(+)]))#

So, if you get one mole of hydronium ions for every one mole of hydrochloric acid, you can say that

#["H"_3"O"^(+)] = ["HCl"] = "0.001 M"#

This means that the pH of the solution will be

#"pH" = - log(0.001)#

#"pH" = color(green)(3)#

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