Solubilities of ammonium tetraphenylborate (NH4BPh4) in water- t- butyl alcohol (TBA) mixed solvents at 283.15,293.15,298.15,303.15 and 308.15 K have been determined by spectrophotometry.The standard Gibbs energy of transfer (Δ G t) of NH4BPh4 from water to H2O- TBA mixtures and the primary medium effect of NH4BPh4 from 283.15 to 308.15 K were studied.The results show that－Δ G t exhibits a complicated variation pattern with the increase in the mole fraction of TBA [x(TBA)] at the same temperature .When x(TBA) < 0.06,－Δ G t increases very slowly with x(TBA),the－Δ G t increases rapidly with x(TBA) when x(TBA) from 0.06 to 0.2.For x(TBA)> 0.2,the－Δ G t decreases with increasing x(TBA).The largest value of －Δ G t occurs at x(TBA) = 0.2.The main reason for this variation was analyzed and discussed.
