What causes conductivity in a solution

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Determination of the conductivity of various solutions

also suitable for Mobile-CASSY 2, Pocket-CASSY and Mobile-CASSY

Load settings

Load example

Experiment description

The electrical conductivity of aqueous solutions depends on several parameters:

a) concentration of the solution, b) degree of dissociation of the substance, c) mobility of the ions and d) size of the charge.

Conclusions can be drawn about these parameters by comparing the measured conductivities of different solutions.

CASSY Lab shows the determined values ​​in an easy-to-read large display and clear diagrams.

Equipment required

1Sensor-CASSY524 010 or 524 013
1CASSY Lab 2524 220
1Chemistry box or conductivity adapter S.524 067(1)
1Conductivity sensor529 670
1Bunsen tripod, 450 mm666 502
1Cross socket666 543
1Universal clamp, 0 ... 25 mm666 551
1Beaker, 100 ml, tall shape664 137
15Volumetric flask, 100 ml665 793
1Volumetric pipette, 25 ml665 976
1Volumetric pipette, 10 ml665 975
2Pipette balls666 003
1spatula666 962
1Watch glass, e.g. 80 mm664 154
1Powder funnel, e.g. 65 mm604 170
1Balance (at least up to 100 g, 
 Resolution 0.01 g) 
1PC with Windows 10 

Required chemicals

D (+) - glucose, e.g. 100 g672 1100
Acetic acid, c = 1 mol / l, e.g. 1000 ml671 9590
Magnesium sulphate 7-hydrate, e.g. 100 g673 1600
Sodium chloride, e.g. 250 g673 5700
Hydrochloric acid, c = 1 mol / l, 500 ml674 6900
least. water 
Possibly.: 
Calibration solution, 1.41 mS / cm667 4641

Preparation of the solutions

Scales, pipettes, volumetric flasks, spatulas, watch glass and funnels are required to prepare the measurement solutions. Three solutions of different concentrations are prepared in each case. Of course, other solutions of other concentrations can be added to the measurement or measured values ​​can be omitted.

1) Glucose solutions (1 mol / l, 0.5 mol / l, 0.1 mol / l)

Exactly 19.82 g (1 mol / l) or 9.91 g (0.5 mol / l) and 1.98 g (0.1 mol / l) glucose are weighed out onto the watch glass lying on the scales and with rinsed distilled water through the funnel into each 100 ml flask. The watch glass, spatula and funnel are then cleaned.

2) acetic acid solutions (0.5 mol / l, 0.1 mol / l, 0.01 mol / l)

With the pipette, 50 ml (0.5 mol / l) or 10 ml (0.1 mol / l) 1 molar acetic acid are put into each 100 ml volumetric flask and filled up to the calibration mark with distilled water. The 0.01 molar acetic acid is made up from 10 ml of 0.1 molar solution in a new flask.

3) Magnesium sulfate solutions (0.5 mol / l, 0.1 mol / l, 0.01 mol / l)

Exactly 12.32 g (0.5 mol / l) or 2.46 g (0.1 mol / l) of magnesium sulfate are weighed onto the watch glass lying on the balance and poured through the funnel into a 100 ml Flask flushed. The 0.01 molar solution is made up with the rinsed pipette from 10 ml 0.1 molar magnesium sulfate solution in a new flask. The watch glass, spatula, funnel and pipette are then cleaned.

4) NaCl solutions (0.5 mol / l, 0.1 mol / l, 0.01 mol / l)

Exactly 2.92 g (0.5 mol / l) sodium chloride are weighed into the watch glass lying on the balance and rinsed with distilled water through the funnel into a 100 ml flask. The 0.1 molar solution is made up with the pipette from 20 ml of the 0.5 molar solution in a new volumetric flask, the 0.01 molar solution from 10 ml of the 0.1 molar solution.

5) hydrochloric acid solution (0.5 mol / l, 0.1 mol / l, 0.01 mol / l)

With cleaned pipettes, 50 ml (0.5 mol / l) or 10 ml (0.1 mol / l) of 1 molar hydrochloric acid are each placed in a 100 ml volumetric flask and filled up to the calibration mark with distilled water. The 0.01 molar solution is made up from 10 ml 0.1 molar HCl in a new flask.

Experimental setup (see sketch)

The chemistry box with the connected conductivity sensor is plugged into input A of the Sensor-CASSY. The conductivity sensor, which is well rinsed with distilled water, is attached to the clamp and can be adjusted in height with the cross sleeve on the stand as required.

calibration

Load settings

The cell constant of the conductivity sensor for the chemistry box is preset to 0.58 in CASSY Lab. If another conductivity sensor is used, its cell constant is in the conductivity settings CA1 under Correct as a factor and the button Correct the factor to operate.

Calibration solutions can be used for a more precise determination of the cell constant. To do this, the beaker and conductivity sensor are first rinsed with distilled water, then with approx. 30-40 ml of calibration solution. The conductivity sensor is dipped into another 50 ml of the calibration solution as for the measurement (keep the distance to the beaker walls), enter the target value in the second line in the correction window and press the button after a stable measured value has been reached Correct the factor.

Carrying out the experiment

Load settings

Adhere to the following sequence for distilled water, glucose solutions, acetic acid, magnesium sulphate, sodium chloride and hydrochloric acid solutions, each starting with the least concentrated solution:

  • Rinse the electrode and beaker well with 30-40 ml of the solution.
  • Pour another approx. 60 ml of the solution into the beaker.
  • Set the conductivity sensor so that it is immersed 2 cm deep in the liquid and is 1 cm away from all walls.
  • If necessary, change the measuring range in the conductivity CA1 settings. The lowest possible measuring range should always be selected.
  • After a stable value has leveled off, take the measured value with take up.
  • Enter the concentration belonging to the measured value and the substance in the diagram. To do this, select Set marker → Text in the diagram's context menu (right mouse button), enter the substance and concentration value using the keyboard and use the mouse to position the text at the desired position in the diagram.
  • For easier evaluation before starting the conductivity measurement with a new substance Measurement → Attach a new series of measurements choose.
  • Before measuring the conductivity with a new material, rinse the beaker and conductivity sensor well with distilled water.

evaluation

The measured values ​​are easy to read thanks to the large display of the display instrument, even for people who are further away. The values ​​are automatically entered as bars in the diagrams so that a clear comparison of the various conductivities is possible.

It becomes clear that the conductivity of a solution is strongly dependent on the concentration. In addition, it can be seen from the test results that strong electrolytes, which dissociate to a large extent, conduct electricity much better than substances that do not dissociate or only dissociate to a small extent. From the higher conductivity of hydrochloric acid compared to saline solutions, conclusions can be drawn about the greater ion mobility of oxonium ions compared to sodium ions.

Despite the higher ion charge, the more concentrated magnesium sulphate solutions have no greater conductivity than the corresponding NaCl solutions, because the ions exert strong electrostatic forces on one another due to their double charge. At low concentrations (large distances between the ions) such as 0.01 mol / l, the conductivity is comparatively higher than with NaCl.

The created diagrams can be printed out via the printer symbol in the upper screen bar.