^{1}Institute of Physics, Daghestan Scientific Center of the RAS, Makhachkala, Russia

**Keywords:** thermal conductivity, sound velocity**property:** thermal properties**material:** aqueous solutions of acids and alkalis

Aqueous solutions of inorganic acids and alkalis have been studied to reveal the structural and other features peculiar only to electrolyte solutions.

These studies were done in order to verify the applicability of the basic equations proposed by Debye, Predvoditelev - Wargaftic, Riedel to estimate the thermal conductivity in the aqueous electrolyte solutions.

In our investigations we used our experimental data on the thermal conductivity in the aqueous solutions of acids and alkalis to reveal the correlation between the thermal conductivity and several basic properties of the matter, such as density, sound velocity, isobaric and isochoric heat capacity.

The aim of these investigations was hyperacoustic vibrations and, in general, the Debye formula validity for the thermal conductance coefficient calculations in the aqueous electrolyte solutions: λ = 1/3 · ( u · c _{v} · ρ · L ). Interesting results were obtained and corresponding conclusions were made.

It is studied the correlation between: thermal conductivity to sound velocity relation (λ_{T}/u_{T}) and volume heat capacity ( c_{p} · ρ; temperature conductivity [ λ_{T} / ( c_{p}· ρ)] and sound velocity ( u_{т}); thermal conductivity (λ_{T}and sound velocity (u_{т}); temperature conductivity [ λ_{T}/ ( c_{р}· ρ)] and characteristic size of liquid (ρ^{1/3}· M^{1/3}).

Riedel formula validity is verified as the correlation between the liquid association degrees in H_{2}O-H_{3}PO_{4} system.

The studies are done with the aim to verify the preservation of association degree in the water and aqueous solution using Predvoditelev - Wargaftic formula, i.e. correlation between the thermal conductivity and ( λ_{p}) and density ρ^{4/3} in the aqueous solution.

It is studied a correlation between the thermal conductivity (λ_{B}/<λ_{p}) and relative solution density (ρ_{p}/ρ_{B}) for the systems: H_{2}O - H_{3}PO_{4}, H_{2}O - H_{2}SO_{4}, H_{2}O - HNO_{3}, H_{2}O - NaOH.

It is shown that the coefficient of thermal conductivity seems to be the structurally sensible property for the electrolyte solutions study.

There found sharp breaks and inflections in the graphs which allow us to make an unambiguous conclusions on the structural changes being held in the binary liquid systems.

We found the connection between the characteristic breaks and eutectic points in the solubility diagram of these systems.

It is also found the correlations between: the temperature factor of the thermal conductivity [(1 / λ) · (Δλ/ΔT)] and concentration; dynamic viscosity (η) and concentration; sound velocity (u_{т}) and concentration, for aqueous solutions of acids and alkalis, from which one can make quality conclusions on electrolyte solution structure and behavior.

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