Pure water at 80 degrees Celsius has pH 6.31. Is it acidic there?

1. Acidity is defined by comparing the hydronium and hydroxide concentrations, not by the number 7. 2. Autoionisation of pure water always makes the two ions in equal amounts. 3. So at 80 degrees Celsius both concentrations are 4.9 x 10^-7 mol per litre. 4. Taking negative logarithms gives pH = 6.31 and pOH = 6.31 as well. 5. Equal values mean equal concentrations, which is the definition of neutral. 6. The familiar 7.00 marker holds only because the constant is 1.0 x 10^-14 at 25 degrees. 7. At 80 degrees an acidic solution is one whose pH falls below 6.31 instead. 8. This matters for processes studied away from standard temperature, such as warm blooded systems. _Source: OpenStax Chemistry (CC BY 4.0), Ch 14 "Acid-Base Equilibria", section 14.2 pH and pOH_