An Oxidation Reduction Potential (ORP) Sensor measures the activity of oxidizers and reducers in an aqueous solution. It is a potentiometric measurement from a two-electrode system similar to a pH sensor. Sometimes it is also referred to as a redox measurement. Unlike a pH sensor, an ORP sensor measures the ratio of oxidized to reduced forms of all chemical species in solution.
The ORP sensor is made up of two electrochemical half cells where the reference electrode is generally Ag/AgCl and the measurement electrode is commonly Pt. The potential difference between the two electrodes represents the redox potential of the solution being measured and can be described by the Nernst equation.
E = Eo – 2.3 (RT/nF) x (log [Ox] / [Red])
E = total potential developed between the measurement and reference electrodes
Eo = a voltage specific to the system
R = gas constant
T = temperature in K
n = the number of electrons involved in the equilibrium between the oxidized and reduced species
F = Faraday constant
[Ox] = concentration of the oxidized species
[Red] = concentration of the reduced form of that species
The output of the ORP sensor is relative to the reference electrode. For example, a reading of +100 mV indicates the potential is 100 mV higher than the potential of the reference half cell and suggests an oxidizing environment. Likewise, a –100 mV reading indicates a potential 100 mV lower than the reference half cell and is a reducing environment. In some applications, redox potential may be reported as Eh which is the voltage reading with respect to the Standard Hydrogen Electrode (SHE). By taking into account the offset of the reference electrode used in the ORP sensor, the potential can be converted into Eh readings. Vernier ORP sensors use a Ag/AgCl saturated KCl reference electrode.
In education, a common application for an ORP sensor is a potentiometric titration. Similar to an acid-base titration, a titrant is added to a sample incrementally until all the sample has reacted and the end-point is reached. One example where students can apply their understanding of redox is by using a Vernier Go Direct ORP Sensor to determine the concentration of H2O2 by titrating the solution with KMnO4. To correctly calculate the concentration, students must understand the balanced redox reaction between KMnO4 and H2O2.
Vernier Tip: Check out two additional experiments from Vernier using an ORP Sensor.
We’re very excited about this release as it includes support for photogates in the most common modes of motion, gate, and pulse timing. It is also the first release of the Android version, which adds support for Go Direct® sensors!
Tangent line analysis feature
Support for Photogate when used with LabQuest interfaces (not yet available on Android)
Lithuanian language support
Android platform now has the same user interface as macOS, Windows, and ChromeOS
Interface can be scaled for larger font size and thicker graph traces
“The mobility of the Vernier Go Direct® Motion Detector opens up new channels of scientific inspection. Of course there is the highly accurate and fast motion detection, but there is also the ability to easily navigate materials and angles, and interference, and most anything else one can think of at the intersection of the Vernier Go Direct® Motion Detector and sound material science (pun intended).”
And, he concludes by saying:
“The word echo, by the way, stems from the story in Greek mythology about a cursed nymph who was doomed to only repeat the last words anyone spoke to her. My guess is today’s students will echo each other when using the Vernier Go Direct® Motion Detector by repeating single words over and over like, “Cool” and “Wow!””
The complete Go Direct family of sensors offers teachers and students maximum versatility to collect scientific data either wirelessly or via a USB connection. These low-cost sensors can be used in more than 300 teacher-tested experiments developed by Vernier and are supported by free graphing and analysis software, the Graphical Analysis™ 4 app.
To inspire students to learn about renewable energy and hone their engineering skills, Vernier supported the 2018 KidWind Challenge, hosted by KidWind. The challenge consists of dozens of local and regional competitions across the country, called KidWind Challenges, during which teams of students test the energy output of wind turbines they designed and built. Students also present their design processes to a panel of judges and participate in short design or problem-solving tasks called “Instant Challenges.”
Teams that take top place at local challenges are invited to the National KidWind Challenge. This year, almost 300 students in grades 4–12 from across the country traveled to Chicago, Illinois, for the National KidWind Challenge on May 8–10, 2018. The event, held during the American Wind Energy Association (AWEA) WINDPOWER 2018 Conference & Exhibition, hosted a total of 21 high school and 40 middle school teams competing for the chance to win the grand prize of $750, the second place prize of $500, and the third place prize of $250.
The 2018 National KidWind Challenge Champions are
High School Division:
First Place – Redwood Express from Bath County High School in Hot Springs, Va.
Second Place – Tuttle Windy’s from Tuttle High School in Tuttle, Okla.
Third Place (Tie) – Silver Bullet from Coachella Valley High School in Thermal, Calif.
Third Place (Tie) – iTurbine X from Old Donation School in Virginia Beach, Va.
Middle School Division:
First Place – Oxford Air Sharks from Oxford Middle School in Oxford, Kan.
Second Place – SPINNERS from Lanier Middle School in Fairfax, Va.
Third Place – The Birds from Darlington Elementary-Middle School in Darlington, Wis.
The Vernier Total Solar Eclipse Campaign recently won a 24th Annual Communicator Award of Distinction in the Integrated Campaign—Business to Consumer category. The campaign was recognized for successfully demonstrating one theme through various forms of media, such as print, social media, video, and more.
With entries received from across the United States and around the world, the Communicator Awards is the largest and most competitive awards program honoring creative excellence for communications professionals. The awards are judged and overseen by the Academy of Interactive and Visual Arts (AIVA), a 600-plus member organization of leading professionals from various disciplines of the visual arts.
The multi-pronged Vernier Total Solar Eclipse Campaign celebrated last summer’s Great American Eclipse by providing tips, resources, and data that STEM teachers could use to teach students about the real-world physical phenomenon throughout the year. Examples of the data collected by educators using Vernier technology are available for free on the Vernier website. Sample data by Dave Vernier was also included in an article about the eclipse in The Physics Teacher.
In addition to the Communicator Award, the Vernier Total Solar Eclipse Campaign also won a One Planet Award and two Stevie® Awards.
The Vernier Total Solar Eclipse Campaign recently won two Stevie® Awards in the 16th Annual American Business Awards®. The campaign won a bronze in both the Branded Content Campaign of the Year and Small-Budget Marketing Campaign of the Year (<$3 million) categories.
This year’s awards program received more than 3,700 nominations from organizations of all sizes and in virtually every industry. More than 200 professionals worldwide participated in the judging process to select the winners.
The Vernier Total Solar Eclipse Campaign celebrated last summer’s Great American Eclipse by providing tips, resources, and data that STEM teachers could use to teach students about the real-world physical phenomenon throughout the year. Examples of the data collected by educators using Vernier technology are available for free on the Vernier website. Sample data by Dave Vernier was also included in an article about the eclipse in The Physics Teacher.
Storing your pH Sensor in storage solution is important for preventing the reference electrolyte from leaching out, keeping the junction clear, and keeping the glass tip hydrated. If you’re out of pH storage solution, Vernier sells premade pH storage solution. As an alternative, you can prepare your own storage solution using a pH 4 buffer. It is recommended that you replace the pH Sensor storage solution annually.
If your pH Sensor was stored dry, immerse the tip in the pH storage solution for a minimum of 8 hours prior to use and then check the response in known buffer solutions. If the reading is close to the known pH of the buffer solution, recalibrating the sensor is recommended. If the readings are off by several pH values, the pH readings do not change when moved from one buffer solution to another different buffer, or the sensor response seems extremely slow, the problem may be more serious. Sometimes a method called “shocking” is used to revive pH electrodes.
Tip #2: Clean Your pH Sensor
Generally, rinsing the tip with DI water should suffice. If the glass tip looks dirty, you can rinse the tip with warm water and a mild household dishwashing detergent (not Alconox detergent). If the tip and bottle appear to have mold growing in or on them, you can clean it with a dilute bleach solution to remove the mold.
Fill the storage bottle with a mixture of 1 part chlorine bleach to 3 or 4 parts water and soak the electrode for 8 minutes.
Thoroughly rinse both in cold or lukewarm water.
Refill the bottle with pH Storage Solution and return the sensor to the bottle.
In biological labs where proteins are used, the glass tip can get fairly dirty. In this case, do the following:
Soak the tip for 10–15 minutes in an acidic pepsin mixture. Approximately 5% pepsin in a 0.001 M HCl solution should work.
Thoroughly rinse the tip in warm tap water.
Refill the storage bottle with pH Storage Solution and return the sensor to the bottle.
Tip #3: Maintain Your pH Calibration Solutions
A new pH Sensor is shipped with a default calibration, but as the sensor ages, it may need to be recalibrated. It is important to use good buffer solutions for calibrating.
To prevent contamination of your buffer solutions, never submerge your sensor right into the bottle. Pour out just what is needed into a container that has been rinsed with DI water and use that for your calibration. Never pour used buffer back into the bottle.
Vernier Tip: Instead of purchasing premade buffer solutions, consider buying buffer capsules. The buffer capsules have a longer shelf life than premade solutions.
A calibration equation is stored on each pH Sensor before it is shipped. For the most accurate measurements with this sensor, we recommend you perform your own 2-point calibration with buffer solutions.
As the pH Sensor ages, the performance of the electrode will change and drift from the saved calibration. Good maintenance and recalibration of the pH Sensor will ensure the readings are accurate.
Preparing the pH Sensor for Calibration
First, remove the storage bottle and rinse the tip with DI water. Never wipe the sensing tip. Instead of wiping the sensing glass, you may blot the tip with a lint-free paper towel to remove excess moisture, but be extra careful not to rub the surface of the glass.
Preparing the Calibration Solutions
To do a two-point calibration for a pH sensor you will need two different pH buffer solutions. Your calibration is only as good as your knowledge of the reference values. For best results, the two calibration points should be widely separated and bracketing the range you anticipate in your experiment. For most chemistry experiments, we recommend buffer solutions of pH 4, 7, and 10. There are multiple ways to obtain these solutions:
Vernier sells a pH buffer kit as pH Buffer Capsule Kit. The kit contains 10 tablets each of buffer pH 4, 7, and 10, and a small bottle of buffer preservative. Each tablet is added to 100 mL of distilled water to prepare the respective pH buffer solutions.
Buffer capsules and prepared buffer solutions are also commonly available through a variety of chemical suppliers.
You can prepare your own buffer solutions using the following recipes:
pH 4.00: Add 2.0 mL of 0.1 M HCl to 1000 mL of 0.1 M potassium hydrogen phthalate.
pH 7.00: Add 582 mL of 0.1 M NaOH to 1000 mL of 0.1 M potassium dihydrogen phosphate.
pH 10.00: Add 214 mL of 0.1 M NaOH to 1000 mL of 0.05 M sodium bicarbonate.
Performing pH Sensor calibration
For the step-by-step instructions to calibrate the pH Sensor, see the list below.