Final answer:
The pH of a 0.04 mM HCl solution is 2.4, and the pH of a 7.0 x 10^-5 M NaOH solution is 9.8.
Step-by-step explanation:
To calculate the pH of a solution, you can use the equation pH = -log[H3O+].
(a) For a 0.04 mM HCl solution, the concentration of H3O+ is 0.04 mM, so the pH can be calculated as pH = -log(0.04 x 10-3) = 2.4.
(b) For a 7.0 x 10-5 M NaOH solution, the concentration of OH- is 7.0 x 10-5 M. To calculate the pOH, we can use the equation pOH = -log[OH-]. Then, pH can be calculated as pH = 14 - pOH.
So, the pOH = -log(7.0 x 10-5) = 4.2, and therefore the pH = 14 - 4.2 = 9.8.