How do pH papers work?

Litmus paper strips are the most universal type, because they measure pH in the widest range from 0 to 14. They belong among the most popular indicator papers precisely thanks to their large range, while still offering relative measuring accuracy.

Whereas phenolphthalein strips are already limited to the pH range of 8.3–10, but they are more accurate.

Do you, however, know how indicator strips work correctly?

In the case of litmus paper strips, the use is completely simple: we immerse the strip for one second in the tested solution and then place it on a non-absorbent surface. The strip will change colour within a few seconds, and based on the colour scale on the package you determine the approximate pH (the most acidic pH is indicated by a deep red colour, which passes through yellow, green up to the blue alkaline pH).

In the case of phenolphthalein strips, the procedure is identical, however the pH is determined on the basis of a different colour change. The strips are white and in the case that the pH of the solution exceeds the limit of 8.3, the strip begins to turn red.

Whereas phenolphthalein strips are already limited to the pH range of 8.3–10, but they are more accurate.

The different colouration is caused by the reaction of the solution to the substance used in the strips (litmus or phenolphthalein), therefore the given colour scale does not apply to all indicator strips and it is always necessary to check which type of strips for measuring pH you are using.

Much more extensive information on the topic of pH measurement can also be found in the blog post Measuring the pH of a product.

The article was prepared for you by

Martina Oboňová

Please send us any of your observations and suggestions to marketing@handymade.sk.

How do pH papers work?

Many of you surely know indicator pH strips.

Do you, however, know how indicator strips work correctly?