Title: Deuterium Oxide
CAS Registry Number: 7789-20-0
Additional Names: Heavy water; water-d2
Molecular Formula: 2H2O
Line Formula: D2O
Properties: More associated than H2O. mp 3.81°; triple point temp 3.82°. bp 101.42°. Critical temp 371.5°. d25 1.1044. Temp of max density 11.23°; d11.23 1.1059. Sp heat of liq (4-25°) 1.028 cal/g/°C. Heat of fusion 1.501 kcal/mole: Long, Kemp, J. Am. Chem. Soc. 58, 1829 (1936). Heat of evapn 9.917 kcal/mole. Dielectric const (25°): 78.06, Vidulich et al., J. Phys. Chem. 71, 656 (1966). Dipole moment in benzene (25°) 1.78, in dioxane 1.87. The surface tension is very slightly smaller and the viscosity at 25° is 1.23 times as great as that of water. On mixing with water, heat is evolved. Reacts with hydrogen at 100° in the presence of 0.2 to 1N NaOH forming DOH + HD + OD-. Ionization const 1.95 ´ 10-15: W. F. K. Wynne-Jones, Trans. Faraday Soc. 32, 1397 (1936). pK (25°) 14.955 (molarity scale); 16.653 (mole fraction scale): A. K. Covington et al., J. Phys. Chem. 70, 3820 (1966). See also Water.
Melting point: mp 3.81°
Boiling point: bp 101.42°
pKa: pK (25°) 14.955 (molarity scale); 16.653 (mole fraction scale): A. K. Covington et al., J. Phys. Chem. 70, 3820 (1966)
Density: d25 1.1044; d11.23 1.1059
Use: To study chemical reaction rates and mechanisms. The cross section of deuterium for the capture of thermal neutrons is very low which makes it useful, in the form of heavy water, as a neutron moderator in nuclear reactors. Produces a considerable decrease in neutron energy per collision.