Final answer:
To find the [OH-] in a solution with a pH of 4.02, subtract the pH from 14 to get the pOH (9.98), and then calculate 10^(-pOH) to find [OH-], yielding 1.05 × 10^-10 M.
Step-by-step explanation:
The question asks for the concentration of hydroxide ions, [OH-], in a solution with a pH of 4.02. To calculate this, we can use the relationship between pH, pOH, and the ionic product of water, Kw.
First, we know that pH + pOH = 14. Given the pH is 4.02, the corresponding pOH can be found by subtracting the pH from 14:
pOH = 14 - pH
= 14 - 4.02
= 9.98
Once we have the pOH, we can find the hydroxide ion concentration:
[OH-] = 10-pOH = 10-9.98
Converting the exponent to a more manageable form, we get [OH-] = 1.05 × 10-10 M.
The solution, with a pH of 4.02, therefore has an [OH-] of 1.05 × 10-10 M, indicating it is an acidic solution because the pH is less than 7.