Fluid-Fluid Systems: Surface Tension Determination of Sodium Chloride and Methanol at Varying Concentrations Using Capillary Method
M.J.Y. Apalin Department of Mining, Metallurgical and Materials Engineering University of the Philippines, Diliman email@example.com
For different interfaces such as soli-liquid interface, air-solid interface and air-liquid interface, surface tension governs. Surface tension is defined as the work needed to increase a liquid's surface area or the force needed to form another surface on the liquid at certain length. Four (4) 100 mL solutions of 0.25M and 0.5M Sodium Chloride (NaCl) solutions and 40:60 and 20:80 Methanol-Water solutions were prepared. The surface tension of each solution was determined using the Capillary Rise Method and was compared to the theoretical values (γmethanol=22.5 dyne/cm; γNaCl =71.97 dyne/cm). A 58.53-118.73% range of percent errors were accumulated which suggest that the method used can efficiently approximate the surface tension of liquids.
Two or more phases of fluid systems may be visually observed from the interface between the phases such as solid-liquid interface, air-solid interface, and air-liquid interface. Figure 1 below shows an air-liquid interface where forces acting on the molecules in the bulk liquid and in the surface are represented. Molecules of the liquid and gas phase (air) which are relatively at distance from the interface are affected by equal forces in all directions (zero net force). Molecules near the interface are exposed to different molecules that of which would yield the net inward attraction force or the unbalanced net force which in the case of the figure is due the lack of liquid molecules above the interface.
Figure 2. Surface Tension between Two Liquid Molecules at Interface Surface tension, denoted by γ (dyne/cm or Nm/m) and as seen on Equation 1, γ = Force/Length (1)
can be defined as a function of work or the force required for...