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Conductivity of ammonium bromide in aqueous butan-2-ol of lower mass fraction

Molar conductivity of dilute solutions of ammonium bromide in binary mixture of butan-2-ol and water with 10 mass. % of alcohol were measured in the temperature range from 15 °C to 35 °C. Data were processed using conductivity model based on the Lee-Wheaton equation. A three-parameter adjustment did not give uniform values for the association distance R. Therefore, the Bjerrum critical distance was chosen as a fixed value of that parameter (R = q). By repeated treatment, the limiting molar conductivity (o) and the ion-pair formation constant (KA) were solved at each temperature, and the thermodynamic quantities of the association reaction (Go, Ho and So) were derived at 25 °C. The obtained thermodynamic quantities, together with Walden product, were compared with literature data for ammonium bromide in mixtures with butan-2-ol mass fraction (w) 70, 80, 90 and 95 %. From the thermodynamic quantities it is seen that the association reaction is spontaneous, endothermic and leads to an increased disorder in the system ; all these features are more pronounced in mixtures with a higher alcohol content.

butan-2-ol + water mixtures; NH4Br; association to ion-pairs; thermodynamic quantities

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