LIQUID DIFFUSIVITY

LIQUID DIFFUSIVITYGroup 4

Mohammed AldahlanNaif AlboainainAli Alghamdi

today we will talk about our experiment

Theory

Fick's laws of diffusiondescribediffusionand its driving force where it can be used to solve for thediffusion coefficient,D.J is the diffusion rate, D is the value of diffusivity and dC/dx is the concentration gradient. The negative sign in the formula indicates that the flow is from high concentration to low concentrationBased on this assumption Ficks law can be written as Where C is conductivity change per unit molar concentration change and dk/dt is rate of conductivity change over time

During the experiment, the concentration at the lower ends is taken to be constantand the concentration at the top end is zeroTraditional liquid diffusion experiments are very time consuming because liquid diffusion is so slow. In this experiment, the diffusion distance is relatively small so we can obtain all the necessary data in a 15- 20 minute experiment.

diffusivity is a function of temperature

procedure five different concentrations of Sodium Chloride (NaCl) solutions were prepared.filling the diffusion cell with the solution the capillary tubes were ensured to be in placeImmersing the cell into 1.4 L of distilled water, until the top of the capillaries was right below the water levelconductivity meter and the magnetic stirrerThis procedure was repeated using different molarity of NaCl solutions.

ensure that there was no air trap insideTraditional liquid diffusion experiments are very time consuming because liquid diffusion is so slow. In this experiment, the diffusion distance is relatively small so we can obtain all the necessary data in a 15- 20 minute experiment.

Result

Slope = 78Used as proportionality factor in calculating the diffusivity

We uesd the six standerds nacl solution to obtaine calibration curve. So we plot conductivity readings versus concentrationAs we can see from the graph we have a linear relationshipthe slope of the line, which give the conductivity change per unit molar concentration change is equal 78This value was used as the proportionality factor in calculating the diffusivity

Result The conductivity increases with timeSlope of the best fit line was used in determining the diffusivity

The conductivity increased for each recording as more of the sodium chloride solution diffused into the waterconductivity has proportional relationship with concentration. The conductivity was plotted vs time to determine the slope of the best fit line. The slope was used in determining the diffusivity of the sodium chloride in water

Result

Result

Result

gas diffusivity in a range of 10E-2 and 10 cm2/secsolids diffusivity in a range of 10E-8 and 10E-30 cm2/sec

the magnitude of the experimental value does fall between those of gas and solid diffusivities. For example, gas diffusivity values range between the orders of 10E-2 and 10 , while diffusivities of solids range between the orders of 10E-8 and 10E-30

we found that the diffusivity at low nacl concentration almost have similar values

simple calculation

After substituting these values in this Equation along with the volume of water in the outer vessel and cross sectional area of the capillary, the value of the diffusion coefficient was found to cm2/s.

conclusion The conductivity for all concentrations increased by time .The results showed that the diffusivity increases as the concentration increases.The hypothesis; the longer the time, the higher the conductivity was accepted.The higher the concentration of the salt solution, the higher the diffusivity of the solution.the higher the concentration of the salt solution, the higher the diffusivity of the solution.

recommendation Be very careful to remove an air bubbles on either side of the interface any bubbles will add significant experimental error.make sure that the device does not shake.improper placement of the probe inside the vessel.

1. Make sure no bubbles appear at conductivity probe. It is because the bubbles can affect the conductivity reading.If the concentration was not uniform, this would affect the values obtained from the conductivity probe, thus affecting the calculated diffusivity

reference

Questions?