Final answer:
To determine the concentration of OH− in a solution with a pH of 10.85, compute the pOH by subtracting the pH from 14, yielding 3.15. Use the formula [OH−] = 10^(-pOH) to calculate the concentration of hydroxide ions, which results in a concentration of about 7.08 x 10^-4 M.
Step-by-step explanation:
To calculate the concentration of OH− in a solution with a pH of 10.85, you must first calculate its pOH. The relationship between pH and pOH is given by the equation pH + pOH = 14. Since the pH of the solution is 10.85, you can calculate the pOH by subtracting the pH from 14: pOH = 14 - 10.85 = 3.15. Next, to find the hydroxide ion concentration, use the formula [OH−] = 10−pOH.
Therefore, [OH−] = 10−3.15 which yields a concentration of approximately 7.08 × 10−4 M.