Question

3) What is the concentration of hydroxide ions in pure water at 30.0°C, if Kw at this temperature is 1.47 10-14? 4) What is the pH of pure water at 40.0°C if the Kw at this temperature is 2.92 x 10-14?

Answer 1

In pure water at 30-degree temperature, the K_w is 1.47 x 10^-14

H₂O=H⁺ + OH^-

^{WE KNOW THAT}

[H⁺] [OH^-] =Kw

[H⁺] [OH^-] = 1.47 x 10^{-14............(1)}

We know that in pure water, the hydroxide concentration must be equal to the hydroxide ion concentration. i,e [H⁺]=[OH^-]

now from equation 1  

we have  

[H⁺]² = 1.47 x 10^-14

taking square root

[H⁺] = 1.21 x 10^-7 mol dm^-3

^{the Concentration of hydroxide concentration is [H+]=[OH-] =1.21 x 10-7 mol dm-3}