The ORP Sensor measures the ability of a solution to act as an oxidizing agent or reducing agent. ORP stands for oxidation-reduction potential. For example, ORP electrodes are often used to measure the oxidizing ability of chlorine in swimming pools, or to determine when the equivalence point has been reached in an oxidation-reduction reaction.

Compatible Software

Quick Start

Calibrating the Sensor

Optional Calibration Procedure

In most experiments done with an ORP Sensor the precise potential in mV is not critical; rather, the large change in potential is the most important factor. As a result, you should not have to perform a new calibration when using the ORP Sensor for most experiments. You can simply use the appropriate calibration that is stored with this auto-ID sensor.

If you are doing water quality testing or performing a chemistry experiment that requires a very accurate calibration, you will need two commercial ORP standards. Using these standards, perform the following calibration, using the
2-point calibration option in all Vernier data-collection programs (this calibration assumes you have two ORP calibration standards, one at 100 mV, another at 300 mV):

• For the first calibration point, rinse the tip of the electrode with distilled water, and place the electrode into the first standard. When the voltage reading displayed by the data-collection program stabilizes, enter the mV value of the first ORP standard (e.g., 100).
• For the second calibration point, remove the electrode from the first standard, rinse it with distilled water, and place it into the second standard. When the voltage stabilizes, enter the mV reading of the second standard (e.g., 300).
• Rinse the electrode with distilled water and place it into the sample. You are now ready to take measurements with the calibrated ORP Sensor.

When you are finished making measurements, rinse the electrode with distilled water. Slide the cap onto the electrode body, and then screw the cap onto the storage bottle so the tip of the electrode is immersed in the storage solution.

Specifications

ORP Electrode

Electrode Amplifier (included with each ORP Sensor)

Suggested Experiments

The ORP Sensor can be used to perform a potentiometric titration. This is a fairly common experiment in AP Chemistry or college general chemistry classes. When a redox titration just exceeds its equivalence point volume, the potential measured by an ORP electrode will increase rapidly (if there is an excess of oxidizing agent) or decrease rapidly (with excess reducing agent), as seen in the graph below.

ORP titration of Fe²⁺ solution with Ce⁴⁺

In the reaction for the titration curve shown previously

Ce⁴⁺ + Fe²+ → Fe³⁺ + Ce³⁺

a solution containing Fe²⁺ of unknown concentration is titrated with an oxidizing agent, ~0.1 M Ce⁴⁺ standard solution (from (NH⁴)₂Ce(NO₃)₆). When the equivalence point is reached, and excess Ce⁴⁺ is added, a large increase in potential results. By examining these data, or performing a second derivative (also shown) or Gran plot, the equivalence point of the titration can easily be determined. With Vernier Graphical Analysis 4 software, the experiment can be done in one of two ways: using the ORP Sensor in Events with Entry mode (where buret volumes are manually entered) or using the Vernier Drop Counter to measure titrant volumes.

Second derivative plot for the titration of Fe²⁺ solution with Ce⁴⁺

Care and Maintenance

Do not completely submerge the sensor. The handle is not waterproof.

Do not wrap the cable tightly around the sensor for storage. Repeatedly doing so can irreparably damage the wires and is not covered under warranty.

How the Sensor Works

Troubleshooting

Repair Information

Warranty

Warranty information for this product can be found on the Support tab at www.vernier.com/orp-bta/#support

General warranty information can be found at www.vernier.com/warranty