The concentration of hydroxide ion in an aqueous solution at 25°C is 3.6 × 10⁻⁴ M. What is the concentration of the hydronium ion?

Answer 1

There is another method of obtaining this answer a bit longer but it is good to getting use to using this method as well when temperature of the solution is not 298 Kelvin (25 degrees Celsius)

[OH-] = 3.6 x10-4 M - Find the [H3O+]

Step 1) Find the pOH of the [OH-]

pOH = -log [OH-}

pOH = -log 3.6 x 10-4 = 3.44

Step 2) From the pOH now calculate the pH

pH + pOH = 14

pH = 14 - 3.44 = 10.56

Step 3) [H3O+] = antilog of -pH

[H3O+] = 2.8 x 10^-11 M

Answer 2

You can use the constant equation to solve:

1.0×10^-14 = [H3O+][OH-],. And plug in the concentration you have been given. You were given [3.6×10^-4] as the concentration for hydroxide ion, now solve for hydronium ion, [H3O+].

1.0x10^-14 = [H3O+][3.6x10^-4]

1.0x10^-14 /= [H3O+]

[3.6x10^-4] = 2.77×10^-11 or 2.8×10^-11, for sig fig purposes.