Question

At a certain temperature, the ph of a neutral solution is 7.61. what is the value of kw at that temperature?

Answer 1

A neutral solution means we are having equal amount of H⁺ and OH⁻. As we know,
                               Kw  =  [H⁺] [OH⁻]      ------ (1)

So, in order to calculate Kw we first need to calculate [H⁺] and [OH⁻],

As,                        pH  =  -log [H⁺]
Or,
                             [H⁺]  =  10⁻ˣ                  ∴ x = pH = 7.61

Putting value, and solving

                             [H⁺]  =  2.45 × 10⁻⁸

As, our system is neutral, so concentration of [OH⁻] is exactly equal to concentration of [H⁺]. Now, putting values of [H⁺] and [OH⁻] in equation 1.

                               Kw  =  [2.45 × 10⁻⁸] [2.45 × 10⁻⁸]

                               Kw  =  6.00 × 10⁻¹⁶