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Calculating the pH of a solution can be done by using the pH formula: pH = -log[H+]

where [H+] represents the hydrogen ion concentration in moles per liter.

For water (H2O):

H20 + H+ → H3O+

The concentration of hydrogen ions, [H+], is equal to the concentration of the hydronium ion, [H3O+], which is 1 x 10-7 M.

Therefore, the pH of pure water is:

pH = -log 1 x 10-7

pH = - (-7)

pH = 7

For NaOH:

NaOH → Na+ + OH-

The concentration of the hydroxide ion, [OH-], is equal to the concentration of NaOH in the solution. So, if the concentration of the NaOH solution is 0.10M, then the concentration of hydroxide ions will also be 0.10M.

Therefore, the pH of 0.10M NaOH is:

pH = -log 0.10

pH = - (-1)

pH = 1

For S2O3:

S2O3 → 2SO4- + 2H+

The concentration of hydrogen ions, [H+], is equal to twice the concentration of sulfuric acid in the solution. So, if the concentration of sulfuric acid is 0.10M, then the concentration of hydrogen ions will also be 0.20M.

Therefore, the pH of 0.10M S2O3 is:

pH = -log 0.20

pH = - (-1.7)

pH = 1.7