Question

At a certain temperature, the ph of a neutral solution is 7.43. what is the value of kw at that temperature? express your answer numerically using two significant figures.

Answer 1

The formula for Kw is:

Kw= [H]*[OH]

where [H] and [OH] are concentrations 

We are given the pH so we can calculate the [H] concentration from the formula:
pH=-log[H] 
7.43 = -log[H]

[H] = 3.715x10^-8 M

In neutral solution, [H] = [OH], therefore: 

[OH]= 3.715x10^-8 M

Calculating Kw:

Kw = (3.715x10^-8)*( 3.715x10^-8)

Kw = 1.38 x 10^-15