Physico-Chemical Properties of Some Alcohols in SDS-Acetonitrile Containing Ternary Systems

Abstract

The critical micelle concentration (CMC) of sodium dodecyl sulfate (SDS) in 80% acetonitrile + 20% water was determined from the conductance and viscosity measurement. They shows a sharp break in their values where micelle starts to form. The estimated CMC of SDS was found to be 0.02 mol. L-1. Densities and viscosities of ternary mixtures of Ethanol + (80% acetonitrile + 20% water + 0.02M SDS), n-Propanol + (80% acetonitrile + 20% water + 0.02M SDS), iso-Propanol +(80% acetonitrile + 20% water + 0.02M SDS),n-Butanol + (80% acetonitrile + 20% water + 0.02M SDS), iso-Butanol + (80% acetonitrile + 20% water + 0.02M SDS), n-Pentanol + (80% acetonitrile + 20% water + 0.02M SDS) and iso-Pentanol + (80% acetonitrile + 20% water + 0.02M SDS) have been studied over the entire range of composition (0 ˂ X2 ˂ 1) at 98.15-323.15K with an interval of 5K. In pure state the density of alcohol has been found to be in the order of: n-Pentanol > Ethanol > n-Butanol > n-Propanol and iso-Pentanol > iso-Butanol > iso-Propanol The values of densities of Alkanols + (80% acetonitrile + 20% water + 0.02M SDS) at equimole fraction solvent systems has been found to be n-Pentanol + (80% acetonitrile + 20% water + 0.02M SDS) > Ethanol + (80% acetonitrile + 20% water + 0.02M SDS) > n-Butanol + (80% acetonitrile + 20% water + 0.02M SDS) > n-Propanol + (80% acetonitrile + 20% water + 0.02M SDS) and iso-Pentanol + (80% acetonitrile + 20% water + 0.02M SDS) > iso-Butanol + (80% acetonitrile + 20% water + 0.02M SDS) > iso-Propanol + (80% acetonitrile + 20% water + 0.02M SDS) The value of the density of alcohols in 80% acetonitrile + 20% water + 0.02M SDS increases with increasing of composition of the alcohols. The densities of all alcohols increase with carbon number which may be depend on the molecular weight of alcohols and structural formula. The densities decrease regularly with increasing of temperature. This is due to the thermal agitation and hence the dipole-dipole interaction or the dissociation of H-bonding are occurred. The excess molar volumes, VE were calculated from the densities of the mixtures at different temperatures. The values of VE for all the systems are negative over the entire range of composition, showing minima at ~ 0.5 mole fraction of Ethanol, ~ 0.8 mole fraction of n-Propanol, ~ 0.8 mole fraction of iso-Propanol, ~ 0.7-0.8 mole fraction of n- Butanol, ~ 0.8 mole fraction of iso-Butanol, ~ 0.7 mole fraction of n-Pentanol, ~ 0.7 mole fraction of iso-Pentanol. The increasing of VE with carbon chain length of alcohols may be related to increase of the size of alcohols. The values of VE for the studied alcohols increase with increase of temperature. The observed values of VE for the mixtures have been explained in terms of physical, chemical and geometrical contributions. The viscosity coefficients, ɳ of all the above mixtures at all the different temperatures have also been determined. The viscosities increase initially slowly up to ~ 0.8 mole fraction of Ethanol, n-Propanol, iso-Propanol, n-Butanol, iso-Butanol, n-Pentanol and iso-Pentanol in 80% acetonitrile + 20% Water + 0.02M SDS systems and later on, the viscosities increases sharply until the pure alcohol is reached specially at lower temperature. In the pure state the viscosity of the alcohols has been found to be in the order of n-Pentanol > n-Butanol > n-Propanol > Ethanol and iso-Pentanol > iso-Butanol > iso-Propanol and iso-Pentanol > n-Pentanol and iso-Butanol > n-Butanol and iso-Propanol > n-Propanol These are a marked decrease in the viscosity with the increase of temperature for all the studied alcohols. This ascribed that the alcohol solutions are less stable at higher temperature. The increasing of viscosity with carbon number of alcohols ascribed that the solution resistance increase with the increase of carbon chain length. The linear dependence of lnɳ against 1/T shows for the all studied alcohols. The branched chain isomers are less stable than linear chain isomers at higher temperature. The excess viscosities, ηE values are found to be negative, indicating that the (80% acetonitrile + 20% water + 0.02M SDS) solutions of alcohols are non-ideal. Excess viscosities are negative at all the temperature over the entire range of composition for all the systems with minima occurring between 0.7-0.8 mole fraction of Ethanol, n-Propanol, iso-Propanol, n-Butanol, iso-Butanol, n-Pentanol and iso-Pentanol. The negative excess viscosities, ηE of the systems indicate that the dissociation of component through dispersion force or steric hindrance. The position of minima virtually does not change remarkably with the variation of temperature. The negative VE, negative ηE and negative  for the systems indicate the segmental inclusion of Acetonitrile in the interstices of polymolecular alkanols aggregate; these will be fewer surfaces available for friction that may results in a reduction of viscosity. For long chain or branched chain alkanols, maximum geometrical for the steric hindrance are occurred. The thermodynamic parameters such as free energy (ΔG#), enthalpy (ΔH#) and entropy (ΔS#) change of activation for the viscous flow for these systems were examined for the entire range of composition. The free energy (ΔG#) were found to be positive in magnitude indicating that the kinetic species involved in forming cavities or holes in the liquid medium is giving by the work required in forming the hole against surface tension of the solution. The excess properties (VE, ηE, ΔG#E) data have been fitted by the least square method to the four parameter Redlich-kister equation and the values of the parameter ai and standard deviation have been reported.