What can you say about the proportion of hydrogen ions and hydroxide ions in a solution that has a pH of 2?
1 Answer
You can say that it contains
Explanation:
In order for an aqueous solution to be neutral, you need it to contain equal concentrations of hydronium ions,
Now, a solution's pH is calculated by taking the negative common logarithm (this is simply a base 10 log) of the concentration of hydronium ions.
#"pH" = - log( ["H"_3"O"^(+)])#
Likewise, a solution's pOH is calculated by taking the negative common logarithm of the concentration of hydroxide ions
#"pOH" = - log( ["OH"^(-)])#
For aqueous solutions, you can say that
#color(blue)("pH" + "pOH" = 14)#
Here
So, take a look at your solution. You know that its pH is equal to
#"pOH" = 14 - "pH"#
#"pOH" = 14 - 2 = 12#
Now, a lower pH is equivalent to a higher concentration of hydronium ions, and implicitly a lower concentration of hydroxide ions.
Use the log definitions of the pH and pOH to get
#["H"_3"O"^(+)] = 10^(-"pH") = 10^(-2)"M"#
and
#["OH"^(-)] = 10^(-"pOH") = 10^(-12)"M"#
This means that a solution that has a pH equal to
#(["H"_3"O"^(+)])/(["OH"^(-)]) = (10^(-2)color(red)(cancel(color(black)("M"))))/(10^(-12)color(red)(cancel(color(black)("M")))) = 10^10#