Question

What is the concentration of hydroxide ions in a solution with a pH of 7.55?

2.82 × 10-8
3.55 × 10-7
9.36 × 10-3
4.17 × 10-11

Answer 1

pH+pOH=14 so we solve for pOH
•pOH=14-7.55 —> 6.45

Now we use the pOH formula
•pOH=-log[OH-] (what’s inside brackets its the concentration of OH)
•6.45=-log[OH] now we pass the negative to the other side
•-6.45=log[OH] and an easy way is to rise 10 by that number
•10^-6.44 = [OH]
•OH= 3.55x10^-7 M