You can work out the concentration of H+ ions (denoted as [H+]) easily on a calculator if you know the pH, which you do. The easiest way to work out [H+] is to do [tex] 10^{-pH} [/tex]. In your case, the maths here would be [tex] 10^{-3.8} [/tex], which gets you an answer of 1.58x[tex] 10^{-4} [/tex], or 0.000158. For 6.2 it would be [tex] 10^{-6.2} [/tex], which gives you 6.31x[tex] 10^{7} [/tex], or 0.00000063. As you can see, the concentration of H+ ions is greater in pH 3.8.
To put it simply, the [H+] decreases the higher up the pH scale you go, and increases as you go lower, but now you know the maths to work it out for yourself too.
