Принцип роботи кондуктометра

Summary

This video is a concise mini-lecture on conductometers, addressing common questions about their settings and usage. It explains the basics of how conductometers measure specific electrical conductivity by calculating resistance and converting it using the cell constant. The video also covers units of measurement like Siemens, Ohms, and EC, the importance of calibration solutions, and the temperature's effect on conductivity readings. Additionally, it discusses different cell constants, calibration techniques, and how conductometers adjust readings based on temperature for more accurate results. Future topics include TDS and salinity.

Takeaways

• 📏 Conductometers measure electrical conductivity by determining resistance and converting it into specific conductivity.
• 🔄 Resistance is measured in Ohms, while electrical conductivity is the inverse of resistance and is measured in Siemens (S).
• ⚙️ The cell constant (C) is crucial for accurate conductivity measurements. It is the ratio of distance between electrodes to the electrode area and helps standardize results.
• 💧 Conductivity depends on the chemical composition of the solution and temperature. Higher salt concentration and temperature increase conductivity.
• 🌡️ Temperature has a direct effect on conductivity, with a typical temperature coefficient of ~1.9%/°C. Modern conductometers adjust readings to a reference temperature, usually 25°C.
• 🧪 Calibration is essential for accuracy. Calibration solutions with known conductivity values, typically based on potassium chloride, are used to determine the cell constant.
• 🌀 Conductometers use alternating current (AC) to avoid polarization of electrodes, which can distort measurements.
• 🧼 Proper maintenance, like rinsing cells with deionized water after each use, ensures accurate readings and extends cell lifespan.
• 📊 Different cell constants are used based on the conductivity range of the solution, e.g., low constants for pure water, higher constants for saltwater.
• 🔍 Some high-end conductometers allow manual input of cell constants for more precise readings, such as the Horiba devices.

Q & A

What is the main function of a conductometer?

A conductometer measures the specific electrical conductivity of a solution by measuring resistance and converting it into electrical conductivity.

Why is the cell constant important in conductometry?

The cell constant is crucial because it helps convert the measured resistance into specific conductivity. It is determined by the distance between the electrodes and the area of the electrodes in the conductometric cell.

How does the temperature affect electrical conductivity?

The electrical conductivity of a solution increases with higher temperatures and decreases with lower temperatures. For most solutions, the specific conductivity changes by about 1.9% per degree Celsius.

What is the significance of calibration standards in conductometry?

Calibration standards, such as solutions with known specific conductivity, are used to determine the cell constant of the conductometer. This allows the device to measure the specific conductivity of other solutions accurately.

What units are used to express electrical conductivity and resistance?

Resistance is measured in Ohms (Ω), while electrical conductivity is the inverse of resistance and is measured in Siemens (S) or microsiemens (μS/cm) for specific conductivity.

Why is alternating current used in conductometers instead of direct current?

Alternating current is used to prevent the electrochemical polarization of the electrodes, which can distort measurement results, especially in high-end conductometers.

What are the typical cell constants used in different conductivity measurements?

Typical cell constants include 0.1, 1.0, 10, and 100, depending on the solution’s electrical conductivity. Lower constants are used for solutions with low conductivity, and higher constants are used for highly conductive solutions like seawater.

What is the role of temperature compensation in conductometers?

Temperature compensation adjusts the measured electrical conductivity to a reference temperature, typically 25°C, ensuring accurate comparisons between measurements taken at different temperatures.

Why do calibration standards often have non-rounded numbers like 1413 μS/cm?

The specific conductivity values of calibration standards correspond to round molar concentrations of potassium chloride in deionized water. These concentrations are set historically and have become de facto standards.

How does contamination of the conductometric cell affect measurements?

Contamination or damage to the cell can alter its constant, leading to inaccurate measurements. It is important to clean the cell thoroughly after use to maintain accuracy.