How does ph meter measure ph？

How does ph meter measure ph？

As we know, changes in the pH value of water bodies will affect biological and chemical reactions in the water body, so the monitoring of pH value is of great significance for water quality management and environmental protection.

It is widely used for continuous monitoring of pH value and temperature in solutions such as thermal power, chemical fertilizers, metallurgy, environmental protection, pharmaceuticals, biochemistry, food and tap water.

However, do you know What is the working principle of pH meter?

The pH sensor consists of two parts: a glass electrode and a reference electrode.

The glass electrode consists of a glass support rod, a glass membrane, an internal reference solution, an internal reference electrode, an electrode cap, and wires. The reference electrode has a known and constant electrode potential and is commonly used as a calomel electrode or a silver/silver chloride electrode.

Since the pH value is related to temperature, a temperature electrode is generally added for temperature compensation to form a three-pole composite electrode.

A hydrogen ion glass electrode and a reference electrode are used to form a primary cell. During the ion exchange process between the glass membrane and the hydrogen ions in the solution being measured, the potential difference between the electrodes is measured to detect the concentration of hydrogen ions in the solution, thus measuring The pH value of the liquid being measured.

When the glass electrode comes into contact with the test solution, some hydrogen ions in the test solution connect with the outer surface of the glass electrode and exchange positions with the metal ions therein. This ion exchange also occurs on the inner surface of the thin glass capsule.

Now, the acidity on the two sides of the glass capsule is different, creating a different charge and a tiny voltage difference between the silver electrode and the potassium chloride. The digital display shows an interpretation of the pH value.

The greater the hydrogen ion activity between the inner and outer surfaces and the greater the voltage difference, the lower the indicated pH (more acidic).

It is important to note that how a pH sensor works may vary depending on the specific sensor type and design. Some advanced pH sensors may use more complex technologies, such as ion-selective electrodes, field-effect transistors, or optical sensors, to improve measurement accuracy and reliability. In addition, the performance of the sensor is also affected by factors such as temperature, solution ionic strength, impurities, etc. Therefore, these factors need to be considered and appropriate compensation and correction must be made in actual use.

What does pH actually measure?

Someone think a pH sensor is a sensor that measures the concentration of hydrogen ions (pH) in a solution.

Is this right?

1. pH is a measure of hydrogen ion concentration. It is defined as the negative logarithm of the hydrogen ion concentration in a substance, measured in moles/liter. For example, under standard conditions (25°C), at 25°C, if the hydrogen ion content in an aqueous solution exceeds 10-7 mol/L, it is considered an acidic solution; if the hydrogen ion content is less than 10-7 mol/L, it is considered an alkaline solution. Acids and bases neutralize each other to form water and salt.

The pH range typically extends from 0 to 14. When an acid is completely ionized in water, its pH is usually 0.0. Acidity describes a substance that has a pH below 7 under standard conditions, where lower pH corresponds to higher hydrogen ion concentrations. When an alkali or base is completely ionized in water, the pH of water is 14.0. Alkalinity describes a substance that has a pH above 7 under standard conditions. Since the pH of pure water is exactly 7.0, it is neither an acid nor a base, but a neutral solution.

In other words, acids are substances that release hydrogen ions (i.e. protons), so if a solution contains more hydrogen ions than neutral water, the solution is considered acidic.

Bases are substances that accept hydrogen ions. When bases dissolve in water, they combine with some of the hydrogen ions formed by the dissociation of the water. Alkaline solutions contain fewer hydrogen ions than neutral water.

2. Ions have either a positive charge (such as H+) or a negative charge (such as OH-). As charge carriers, all dissolved ions exert an electrical force on their surroundings. While a solution may be electrically neutral on the macroscopic scale, the influence of ions can be dramatic on the microscopic scale.

Solutions with relatively high ion concentrations may produce abnormally low ion concentration measurements. Therefore, the solution begins to behave as if certain ions are no longer present. This apparent ion loss is caused by the interaction of ions in solution, ultimately leading to significant deviations from ideal behavior. In order to account for this interaction, ion activity (also called effective ion concentration) must be considered instead of ion concentration.

Therefore, pH is a measure of hydrogen ion activity.

But sometimes, the concentration of ions and the activity of ions are the same.