🧪 Water Ionization & pH Lab

Investigate water's auto-protolysis equilibrium ($2\text{H}_2\text{O} \rightleftharpoons \text{H}_3\text{O}^+ + \text{OH}^-$). Discover why neutral water is $\text{pH } 7.00$ only at $25^\circ\text{C}$, shifting to $\text{pH } 6.81$ at body temp ($37^\circ\text{C}$) and $\text{pH } 6.14$ at boiling ($100^\circ\text{C}$).

Water Temperature ($T$) °C

Measured Solution pH Leave blank for pure neutral water

Acidic ([H⁺] > [OH⁻]) True Neutral Point: pH 7.00 Basic ([OH⁻] > [H⁺])

Neutral Water pH

7.00

$pK_w = 14.00$

Ion Product ($K_w$)

1.00 × 10⁻¹⁴

$\text{mol}^2/\text{L}^2$

Hydronium Concentration

1.00 × 10⁻⁷ M

[OH⁻] = 1.00 × 10⁻⁷ M

Solution Nature

PURE NEUTRAL

ΔH° = +55.8 kJ/mol (Endothermic)

Biomedical Insight: At human body temperature (37°C), pure water has a pH of 6.81, not 7.00! Because auto-ionization is endothermic, heat drives dissociation forward. Arterial blood pH of 7.40 at 37°C is actually slightly alkaline relative to neutral water.