Lab Report #8

A Study of Factors Affecting the Rate of Diffusion Through a Membrane

Procedure

The three factors affecting the rate of diffusion of sodium chloride (NaCl) across a dialysis tubing membrane were: NaCl concentration, possible interference with sucrose, and temperature. Each eighth grade class section was responsible for one of the three factors.

Three concentrations of 1%, 5%, and 10% (by weight, 1.0 g/100 ml) NaCl were prepared. Three “cell models” were prepared by clamping the ends of 8-10 cm. presoaked dialysis tubing after filling with 12-15 ml of salt solution.

One cell model was filled with 8 ml 5% NaCl plus 8 ml 5% sucrose solutions.

Three water baths: icy (6ºC), room temperature (19ºC), and warm water (53ºC), were prepared, into which a cell model containing 5% NaCl solution was placed.

Each “cell model” was placed in a large beaker with 300 ml distilled water. A conductivity probe (connected to a computer with LoggerPro graphic analysis software) was placed in the beaker. The conductivity measurements of the water baths ran a minimum of 2 minutes. Students gently stirred the water bath for the duration of the experimental run. The data was plotted as conductivity (mg/L) versus time. A sample was taken every 2 seconds.