What is the pH of a 0.01 M solution of the strong acid #HNO_3# in water?

1 Answer
Stefan V.
Jan 4, 2016

#"pH" = 2#

Explanation:

The important thing to keep in mind when dealing with strong acids is that they dissociate completely in aqueous solution to form hydronium ions, #"H"_3"O"^(+)#, and their conjugate base.

Complete dissociation means that every molecule of acid will ionize, i.e. donate its acidic proton to a water molecule.

That tells you that a strong monoprotic acid will produce hydronium ions in a #1:1# mole ratio, that is, every mole of acid will produce one mole of hydronium ions.

http://cikguwong.blogspot.ro/2011/08/chemistry-form-4-chapter-7-strength-of.html

In this case, nitric acid will dissociate to form

#"HNO"_text(3(aq]) + "H"_2"O"_text((l]) -> "H"_3"O"_text((aq])^(+) + "NO"_text(3(aq])^(-)#

This means that the concentration of hydronium ions will be equal to that of the nitric acid

#["H"_3"O"^(+)] = ["HNO"_3] = "0.01 M"#

As you know, a solution's pH is simply a measure of its concentration of hydronium ions

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

In this case, the pH of the solution will be

#"pH" = - log(0.01) = color(green)(2)#

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