The investigation of the dependence of solution refraction index on its concentration

Laboratorywork

Topic: The investigation of the dependence of solution refraction index on its concentration. Finding of solution concentration with using the refractometer.

Description of device and principle of its work:

Principle of work is based on the phenomenon of total inner reflection at the passing the light trough the boundary of division of two mediums with various refraction indexes. With using of refractometer investigate the solutions with refraction index from 1.3 to 1.5.

Measurements are conducting at the illumination by the «white» light (daylight or candlelight). Refraction index for transparent medium finds in passing light.

Light passes through the lighting prism 2 (fig.1); it scatters by the mat edge of prism. Scattering light passes to the being investigated liquid and it is refracted on the boundary of liquid and measuring prism 1. Then the light passes through the compensators of dispersion, objective, prism, grid of scale, ocular and proceed to the eye of observe.

At the observation into the ocular 3, the boundary of light and shade and the touch of grid are aligned with using the screw «И» 7, and take a reading of refraction index from the scale (ocular 3, fig.1).

Revolving compensator of dispersion «К» 6 serves for removal of achromatization of light and shade boundary.

1.  Adjustment of device:

–  Verify the adjustment of refractometer with using the calibration sample (distilled water): make the spot test (distilled water) on the measuring prism and close down the lighting prism. Find the image in ocular.

–  Revolve the screw «И» to the appearance of light-shade boundary.

–  Remove the coloring of light-shade boundary by the turn of screw «К».

–  Align the touch of grid with the light-shade boundary (by the screw «К») and take a reading for the refraction index from scale of ocular. At the correct adjustment of refractometer the maximum reading correspond to the refraction index of distilling water n_о.

–  Repeat the reading three times.

–  Find the average measures of refraction index.

2.  Measurement of refraction index for given solution:

–  Make the spot test (for given solution) on the measuring prism and close down the lighting prism.

–  Revolve the screw «И» until the appearance of light-shade boundary in the field of vision of ocular.

–  Revolve the screw «К» until the disappearance of the coloring boundary line.

–  Align the touch of grid with the light-shade boundary (by the screw «И») and take a reading for the refraction index from scale of ocular.

–  Repeat of measurement the three times.

Remark:

Clean the surface of prism before the each measurement and after the each measurement by the soft napkin.

3.  Begin again from step 2 for various solutions (several concentration).

4.  Fill tables:

Table 1

Table2

5.  Draw the graphic of dependence of refraction index n_ave for the solution on its concentration С%.

6.  Find with the using of graphic the concentration of unknown solution.

7.  Draw the conclusion.