Question

If the hydroxide ion concentration in a lake is 10‐10 M what is the lake’s pH?

Answer 1

pOH = -log(OH^-). Solve for pOH.
Then pH + pOH = 14.
Solve for pH.

Answer 2

but when its hydrogen ions, do i use that second equation? ph+poh=14?

Answer 3

The liquid in the stomach has a pH of approximately 2. What is the concentration of hydrogen ions in
this liquid?

Answer 4

for hydroxide ion, there's an additional step to find pH.

after finding pOH, you'd have to plug it into the second equation and solve for pH.

if you were given hydrogen ions, you could find pH in one step.
pH= -log(H^+)

the concentration of hydrogen ions is essentially 10^(-pH)