Question

"a cup of black coffee has a ph of 5. what is the hydrogen ion concentration of this cup of coffee?

Answer 1

the negative antilog of 5 is the concentration of H+...
i.e. 10 raise to power -5

Answer 2

The hydrogen ion concentration of a cup of coffee can be found as follows.

We know that $pH =-\log \left[\mathrm{H}^{+}\right]$

And we also know that $\left[\mathrm{H}^{+}\right]=10^{-\mathrm{pH}}$

pH measures the concentration of hydrogen ions in a solution. Any solution that has high concentration of hydrogen ions has a low pH while those solutions that have low concentration of hydrogen ions have a high pH.  

We are given that the black coffee has a pH of 5.

So, we can use the value of pH in the above equation to find the value of the concentration of hydrogen ion.  

$\bold{\left[\mathrm{H}^{+}\right]=10^{-5}}$