Since 1991 Sentek has been providing a range of electrochemical sensors for use in science, industry and education. Many schools and colleges will use educational electrodes as part of their practical lessons, to help educate students on measurement and analysis techniques.

Measurement using pH sensors can help students with a practical understanding of the theory they are learning in the classroom. Many industries use pH as an important part of their testing and QC procedures, therefore having a basic understanding of the measuring system and how it works could prove beneficial in their future careers. These industries include science-based roles in laboratories, but also extends to agriculture, food, manufacturing, cosmetics and many more.

In addition to providing students with a familiarity of the equipment, using pH educational electrodes also teaches students valuable skills in calibration, validation and following good laboratory practice guidelines.

Common experiments include:

• Determining the pH of many common household items
• Comparison of pH from using litmus paper vs pH electrode and meter
• Monitoring pH of a chemical reaction
• Comparing pH of water from a variety of sources

How pH electrodes work

pH is a measurement of hydrogen ion activity in a solution, and is measured on a scale of 0-14. Two electrodes are required in order to complete an electrical circuit and give a reading from a pH meter. These are the pH cell and the reference cell, and in most of Sentek’s range, both electrodes are within the same body to form a combination electrode.

The pH cell is made up of a glass membrane, which is specially formulated to be sensitive to hydrogen ions. When the glass membrane comes into contact with an aqueous sample, a hydrated layer forms on the inside and outside of the membrane. Hydrogen ions will transfer across this membrane, and the direction of the transfer depends on whether the sample is acidic or alkaline. The difference between the inner and outer charge gives a membrane potential which can be compared to the stable reference potential to measure the pH value. The reference cell is stable as it is in contact with the sample through a junction rather than a hydrogen sensitive membrane. A meter calculates the difference in the pH and reference cell potential and gives a value in millivolts or is converted to pH units.

Using pH electrodes in school science experiments

School Science Experiment 1: Acid or Alkaline?

The chemistry of acids and bases can be investigated by using a pH electrode connected to a pH meter. Students can learn how to use the equipment by measuring the pH of everyday items to determine if they have an acidic or alkaline pH. Examples can include lemon juice (pH2), vinegar (pH3) and bleach (pH 11-13). This practical experiment will help give a practical understanding to the theory they are learning in class.

School Science Experiment 2: Diluting acids and alkalis

Students can measure the pH of a sample of choice, such as a weakly acidic solution. They can then dilute the sample with deionised water, and monitor the change in pH. This can also be done with an alkali sample, which will do the reverse – the pH will decrease as the sample becomes diluted.

Our range

Sentek are able to offer a range of budget friendly, durable sensors that are perfect for the educational sector.

Our EP14 offers an effective electrode for the educational market, combining quality at an affordable price. It is a low maintenance, gel filled combination electrode, with a cotton junction that is suitable for aqueous samples.

Our P14 and P17 both have robust epoxy bodies, teflon junctions which are resistant to blockages, and they require very little maintenance making them perfect for educational settings. Our P17 is perfect for surface measurements, whereas the P14 has a bulb membrane which can give faster and more accurate readings.

We also offer a refillable P14 Educational electrode kit; P14/RF/Kit. The kit comes complete with 30ml Partial Gel and plastic syringe which is used to refill the electrode, along with 30ml Cleaning Solution and 30ml Storage Solution. This is a perfect starter kit for beginners.

We can also offer accessories such as colour coded buffer solutions and swing electrode arms to assist with the calibration and measurement process.

Sentek offer free technical support for our customers both in the UK and abroad. We are here to help advise which of our probes are most suited to your application, advise you on how get the best from your electrode, or any technical query you may have.

Author: Amy Measor