Investigation of water structure changes in solutions: H2O-CO(NH2)2 - phosphate [K3PO4, K2HPO4, KH2PO4] using ultraacoustic method

Abstract

It is investigated how carbamide and potassium phosphates dissolved together and separately influence water structure. The change of water structure has been investigated by ultraacoustic and densimetric methods, while measuring speed and density of ultrasound in solutions and counting adiabatic compressibility from them. It is established that the speed of ultrasound increases and adiabatic compressibility lessens, when concentration of carbamide increases. Phosphates enlarge the speed of ultrasound and lessen adiabatic compressibility in solutions. Potassium phosphate has the greatest influence there. A large polarised uncompressible layer of water molecules around cations causes lessening of adiabatic compressibility in a solution of potassium phosphate. Uncompressible volume of one molecule of dissolved salt and average uncompressible volume of one molecule of two salts dissolved together have been calculated from the coefficients of adiabatic compressibility. The hydration quantity of phosphate ions is estimated from the difference Dv of average uncompressible volume of one molecule of two salts dissolved together and separately. The change of Dv is the largest when concentration of carbamide is small. The change of Dv lessens when concentration of carbamide increases. The change of Dv is very small when concentration of carbamide is larger than 5%. It is established that hydration of phosphates ions is the largest when phosphate and carbamide are dissolved separately. It is presented in the work that ions in a solution can be divided into two groups - hard and soft - according to the theory of compressibility. Hard ions have a strong polarised layer of water molecules.