Question

If the ionization constant of water, kw, at 40°c is 2.92 × 10-14, then what is the hydronium ion concentration and ph for an acidic solution?

Answer 1

The formula for Kw is:  

Kw = [H+] [OH-]  

For water, [H+] = [OH-]  

Therefore we can write  

Kw = [H+]²

For the temperature (40C) given,  

Kw = 2.92 x 10^-14  

[H+]² = 2.92 x 10^-14  

[H+] = √(2.92 x 10^-14)  

[H+] = 1.71 x 10^-7  

To determine the pH :  

pH = -log [H+]  

pH = -log (1.71 x 10^-7)  

pH = 6.76

Answer 2

Answer is: the hydronium ion concentratio is 1.71×10⁻⁷ mol/dm³ and pH<6.76.

The Kw (the ionization constant of water) at 40°C is 2.94×10⁻¹⁴ mol²/dm⁶ or 2.94×10⁻¹⁴ M².

Kw = [H₃O⁺] · [OH⁻].

[H₃O⁺] = [OH⁻] = x.

Kw = x².

x = √Kw.

x = √2.94×10⁻¹⁴ M².

x = [H₃O⁺] = 1.71×10⁻⁷ M; concentration of hydronium ion.

pH = -log[H₃O⁺].

pH = -log(1.71×10⁻⁷ M).

pH = 6.76.

pH (potential of hydrogen) is a numeric scale used to specify the acidity or basicity an aqueous solution.