The dissociation constant for water increases with T (Log K[sub]W[/sub] becomes less negative) according to
Log K[sub]W[/sub] = -4470.99/T + 6.0875 - 0.01706 T
where T is degrees K, and pH = -0.5 x Log K[sub]W[/sub].
For 573 K, this equation gives pH = -5.7 cf. the ~5.5 value given by Metalguy.
Source: M. Whitfield, in Chemical Oceanography, J. P. Riley and Skirrow, Eds., Vol. 1, 2nd ed., Academic, New York, 1975, pp. 44-171. Cited by