To make an acid solution, 6.8 x 10-3 mole of a strong acid (6.8 x 10-3 mole H3O+) is
dissolved in water to give a 550 mL solution. What is the pH and [OH-] of the solution?
To find the pH and [OH-] of the solution, we need to use the concept of concentration and the relation between pH, [H3O+], and [OH-].
Step 1: Convert the volume of the solution from mL to L:
550 mL = 550/1000 = 0.55 L
Step 2: Calculate the concentration of the acid (H3O+):
Concentration (C) = moles/volume
C = (6.8 x 10^-3 mole) / (0.55 L)
C ≈ 0.012 M
Step 3: Calculate the pH of the solution:
pH = -log [H3O+]
pH = -log (0.012)
pH ≈ 1.92
Step 4: Calculate the concentration of hydroxide ions ([OH-]):
In water, the product of [H3O+] and [OH-] is always constant at 1 x 10^-14 M^2:
[H3O+][OH-] = 1 x 10^-14 M^2
Since we have the concentration of [H3O+], we can rearrange the equation to solve for [OH-]:
[OH-] = (1 x 10^-14 M^2) / [H3O+]
[OH-] = (1 x 10^-14 M^2) / (0.012 M)
[OH-] ≈ 8.33 x 10^-13 M
Therefore, the pH of the solution is approximately 1.92, and the concentration of [OH-] is approximately 8.33 x 10^-13 M.