Abstract
A conductimetric technique is used to measure thermal diffusion in aqueous solutions of sodium carbonate. In dilute solutions hydrolysis produces significant amounts of sodium bicarbonate and sodium hydroxide: Na2CO3 + H2O = NaHCO3 + NaOH. The applied temperature gradient causes the various solutes to migrate to the cooler parts of the solution. NaOH is found to diffuse more rapidly than NaHCO3, leading to the accumulation of excess NaOH (relative to NaHCO3) at the cold plate. Binary Na2CO3(m) + H2O mixtures therefore separate into ternary Na2CO3(m1) + NaOH(m2) + H2O mixtures under nonisothermal conditions. The steady-state molality gradients dm1/dT and dm2/dT and the ternary heats of transport of aqueous Na2CO3 and NaOH are reported. Key words: aqueous sodium carbonate, hydrolysis, mixed electrolytes, Soret coefficient, thermal diffusion.
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