Calculate the pH...

Question

Calculate the pH of each solution given the following [H3O+] or [OH-] values.

[H3O+] = 5.0×10⁻⁸ M

[H3O+] = 5.5×10⁻⁶ M

[OH−] = 4.5×10⁻² M

[OH−] = 6.0×10⁻³ M

[H3O+] = 5.4×10⁻² M

[OH−] = 7.4×10⁻⁴ M

Answer 1

pH = pOH = 14

pH = 14 - pOH

pOH = 14 - pH

pH = -log [H₃O⁺]

pOH = -log [OH-]

[H3O][OH-] = 1x10^-14

Memorize the above relationships

(1) [H3O+] = 5.0x10^-8

pH = -log 5.0x10^{-8 =} 7.3

(2) [H3O⁺] = 5.5x10^-6

pH = -log 5.5x10^-6 = 5.3

(3) [OH-] = 4.5x10^-2

pH = 14 - pOH and pOH = -log [OH-] = -log 4.5x10^-2 = 1.3

pH = 14 - 1.3 = 12.7

Or you could use [H₃O⁺][OH-] = 1x10^-14 and solve for [H₃O⁺]

[H₃O⁺] = 1x10^-14/4.5x10^-2 = 2.2x10^-13 and pH = -log 2.2x10^-13 = 12.7 (same answer as above)

You should be able to do the rest by yourself