Many of you are certainly familiar with indicator pH strips. But do you know how to use them correctly and read the result? We will look at two types — litmus and phenolphthalein strips — at how they work and how they differ from each other.
About this article
The article was prepared for you by Martina Oboňová. In it we will go through the pH scales, the correct measuring procedure with an indicator strip and the difference between litmus and phenolphthalein strips — including why the colour scale on the packaging does not apply to every type of strip.
Main benefits
- The widest measuring range
Litmus strips are the most versatile type, because they measure pH in the widest range from 0 to 14.
- A popular combination
They are among the most popular indicator strips precisely thanks to their wide range, while still offering relatively accurate measurement.
- More accurate measurement in a narrow band
Phenolphthalein strips are limited to a pH range of 8.3–10, but they are more accurate.
- A quick result
You only need to immerse the strip in the solution for one second — it changes colour within a few seconds.
- Simple evaluation
You determine the approximate pH by comparing it with the colour scale given on the packaging.
Properties of indicator strips
The pH scales
First of all, it is necessary to know the individual pH scales:
- acidic environment has values of 0–7
- alkaline environment has values of 7–14
- neutral environment is 7
Litmus strips
Litmus strips are the most versatile type, because they measure pH in the widest range from 0 to 14. They are among the most popular indicator strips precisely thanks to their wide range, while still offering relatively accurate measurement.
Their use is completely simple: we immerse the strip for one second into 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 packaging you determine the approximate pH — the most acidic pH is indicated by an intense red colour, which passes through yellow and green up to blue alkaline pH.
Its main function is to determine whether your liquid is acidic, alkaline or neutral.
Phenolphthalein strips
In the case of phenolphthalein strips the procedure is identical, however the pH is determined based on a different colour change. The strips are white and if the pH of the solution exceeds the limit of 8.3, the strip begins to turn red.
Phenolphthalein strips are already limited to a pH range of 8.3–10, but they are more accurate.
The measuring procedure
- Immerse the strip 1 second
We immerse the strip for one second into the tested solution.
- Place it on a surface
We then place the strip on a non-absorbent surface.
- Colour change a few seconds
The strip will change colour within a few seconds.
- Reading the result
Based on the colour scale on the packaging you determine the approximate pH. The most acidic pH is indicated by an intense red colour, which passes through yellow and green up to blue alkaline pH. With phenolphthalein strips the procedure is identical, only the pH is determined by a different colour change — a white strip turns red above the limit of pH 8.3.
Always check the type of strip: the different colour 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 pH measuring strips you are using.
Frequently asked questions about pH strips
Practical questions about indicator strips — ranges, the measuring procedure and the differences between the individual types.
What pH range do litmus strips measure?
They measure pH in the widest range from 0 to 14, which makes them the most versatile type. They are among the most popular precisely thanks to their wide range, while still offering relatively accurate measurement.
How is an indicator strip used correctly?
Immerse the strip in the tested solution for one second and then place it on a non-absorbent surface. It will change colour within a few seconds and you determine the approximate pH from the colour scale on the packaging.
How do phenolphthalein strips differ?
They are white and only turn red once the pH of the solution exceeds the limit of 8.3. Their range is limited to pH 8.3–10, but they are more accurate.
Does the colour scale apply to all indicator strips?
No. The different colour 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 you are using to measure pH.
What do the individual values on the pH scale mean?
An acidic environment has values of 0–7, an alkaline environment values of 7–14 and a neutral environment is 7.
Conclusion
Much more extensive information on the topic of pH measurement can 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 [email protected].
You will find indicator strips for measuring pH in the Handymade range.
