Final answer:
The hydroxide ion concentration (OH-) of a solution with a pH of 10.81 is calculated by finding the pOH (3.19) from the relationship pH + pOH = 14. Then, [OH-] = 10^-pOH, which gives 6.46 x 10^-4 M. The correct answer, rounded to significant figures, is 6.5 x 10^-4 M (Option A).
Step-by-step explanation:
To determine the hydroxide ion concentration (OH-) of a solution with a pH of 10.81, we need to calculate the pOH and then use it to find the [OH-]. First, remember that pH + pOH = 14. Subtracting the given pH from 14 gives us the pOH:
pOH = 14 - pH
pOH = 14 - 10.81
pOH = 3.19
Once we have the pOH, we find the [OH-] by the following:
[OH-] = 10-pOH
[OH-] = 10-3.19
[OH-] = 6.46 x 10-4 M
Therefore, the correct answer is A. 6.5 x 10-4 M, since we usually round to the nearest digit when dealing with significant figures in the context of scientific measurements.