Conductivity method to determine the purity of water experiment

Summary

This experiment is from the official website of College of Chemistry, Qingdao University of Science and Technology.

Operation method

Conductivity method to determine the purity of water experiment

Principle

Ions in an aqueous solution of an electrolyte are capable of directional movement in the presence of an electric field and, therefore, have electrical conductivity. The magnitude of its ability to conduct electricity is called conductivity. Within a certain range, the concentration of an electrolyte solution is linearly related to the magnitude of its conductivity. Therefore, based on the measurement of the conductivity of water can know the concentration of ions in water, that is, know the purity of water. To measure the conductivity, two electrodes can be inserted into the solution to measure the resistance between the two electrodes R. R = ρ (L/A) where: ρ - resistivity; L - the distance between the two electrodes; A - the electrode area; the inverse of R is the conductance L, and the inverse of ρ is the conductivity K. L = K (A/L) is generally used L=K(A/L)θ=L/A is generally used as the constant of the conductivity cell, and the domestic DDS-11A type conductivity meter can correct the electrode constant. Other models need to calculate the correction. The electrode constant can be obtained by measuring the conductance of the electrode in a certain concentration of KCl solution (standard solution). Because θ = K/L, K (conductivity) is the conductivity of KCl solution at a certain temperature, which can be found in the manual, and L is the conductivity measured under the same experimental conditions, θ can be found.

Materials and Instruments

KCl Standard Solution
DDS-11A Conductivity Meter Conductivity Electrode

Move

1. Adjust the instrument according to the instructions of DDS-11A conductivity meter, wash the electrode and container with the measured solution 2-3 times, then insert the electrode into the solution, set the knob of the conductivity meter to "Measurement", and the range selector switch will be lowered to the appropriate position gear by gear, and read out the readings on the table, and then measure the conductivity of various kinds of water and compare their purity, respectively. Conductivity of water, and compare their purity.

2. Conductivity cell constant correction

DDS-11A type conductivity meter attached to the supporting electrodes, the factory have indicated its electrode constant, we can be corrected through the following experiments. Accurately suck 0.1000 mol/L KCl solution 10.00 mL and 20.00 mL, respectively, in a 100 mL volumetric flask, prepared as 0.0100 mol/L and 0.0200 mol/L KCl standard solution, and then put the electrode with the electrode constants specified in the factory into this solution (the conductivity of the solution can be found out from the manual). Turn the instrument switch to "Measurement", adjust the calibration adjuster so that the meter head indicates the found value, then return the switch ④ to calibration, do not move the switch ⑤, adjust the electrode constant adjuster so that the meter head is full. At this time, the value shown in the electrode constant regulator should be the electrode constant of the electrode.

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