What is pH and how to measure it?

‘pH’, or power of hydrogen, is something that must be taken into consideration when handling chemical substances. It is important that the pH level of liquid solutions is maintained at an appropriate level to prevent unnecessary reactions from occuring. This article will explain pH level measurement in different work environments.

What is pH?

pH is an index that expresses the concentration of hydrogen ions, and specifically, it was created to quantify and express the degree of acidity or alkalinity of a substance. A pH value of 7 indicates neutrality; below this value, a lower value indicates a stronger acidity, and above this value, a higher value indicates a stronger alkalinity. It should be noted that when the pH changes by one, the hydrogen ion concentration changes by 10 times or 1/10.

When measuring pH

Various chemical reactions are utilized in the field of chemistry. When chemical reactions are used, there are many cases where the pH of an object or sub-material has a significant impact on the finished product. 

Below is a reference where pH measurements are used. 

Metal processing

The pH adjustment of solutions is performed in metal processing. To ensure that only necessary metals are extracted and unnecessary metals are not dissolved, the dissolving solution is kept at an appropriate pH level.

Plastic processing

In plastic processing, pH control is performed during polymerization, condensation, and other so-called polymerization processes.

Plating

In the plating process, pH control of the plating solution is performed to produce beautiful colors and luster. Especially in acidic plating solutions, improper pH control can easily cause defects, such as the plating peeling off easily, as well as ruining the aesthetics of the product.

Painting

In painting, the pH of the surface treatment solution is controlled to maintain an appropriate pH level in order to enhance the quality of the finish.

Cutting and polishing processes

In cutting and polishing processes, if the condition of the metalworking fluids (water-soluble cutting and grinding fluids) is not appropriate or has deteriorated, it can cause rust and uneven surface coatings. Therefore, it is ideal to incorporate concentration and pH control regularly.

Construction sites

At construction sites, pH is checked to confirm substrate surface. If the pH of the substrate is not appropriate, defects such as discoloration, uneven color, peeling, and blistering are likely to occur in the coating. Moisture content should be maintained at 5-6% by a mortar moisture meter, and pH should be less than -9 with a pH meter or pH test paper.

Methods of pH measurement

Litmus paper

Litmus is a purple dye found in plants, and paper infused with this dye is called litmus paper. Litmus paper is a widely used measurement method for simple acidity/alkalinity check, as it can simply distinguish between acidity and alkalinity. When litmus paper is dipped into a liquid solution, it shows red for acidity of pH < 4.5 and blue for pH > 8.3. There are two types of litmus paper: red in the neutral state (shipping state) and blue, and it is common to use both types to check the discoloration.

リトマス紙

pH indicator

A pH indicator is an easy way to measure the pH of a clear, colorless liquid. Typical examples are BTB solution and red cabbage dye. BTB solution is an indicator that shows mainly neutral green color, yellow color for acidity, and blue color for alkalinity, and is ideal for simply determining whether a liquid is acidic or alkaline. Red cabbage dye is a natural dye derived from red cabbage.

pH指示薬

Hydrogen electrode

This is a measurement method using a platinum electrode (hydrogen electrode) to which hydrogen gas is adsorbed. When the hydrogen electrode is immersed in the liquid solution, an electric potential is generated in accordance with the hydrogen ion concentration in the solution, and the pH value is determined from this potential value. However, be aware of the danger of hydrogen gas explosions.

pH meter

A pH meter is an electrical machine with a glass electrode inside. By measuring the potential generated between the reference solution inside the glass electrode of the pH meter and the solution to be measured, the pH of the liquid solution can be accurately measured.

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Summary

Managing pH levels is an essential task in a variety of sites that use different chemicals. To maintain the quality and durability of a finished product, it is important to keep the pH level at a proper level.