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Phenolphthalein Indicator

Phenolphthalein Indicator Solution is used as an base/acid indicator.  When in contact with the presence of acid (or a lower pH solution such as water), the solution will turn colorless.  As the pH of the mixture increases, a pink tint or violet color appears.  This makes many unique applications.  This is a detection that the product has a higher pH.

Here are some common applications:

Water Leak Detection

In large industrial closed loop water applications, Phenolphthalein is added to the water  system to tint the water pink.  The plant can then be walked to determine the leak location.  It can be easily disposed with water to drive the water pH below 8, where the pink tine vanishes.

Blood Test Application

Phenolphthalein Indicators are used to perform a presumptive blood test (Kastle-Meyer Test).

A dry sample is obtained with a filter paper or swab. A few drops of alcohols is added followed by a few drops of phenolphthalein indicator.  The final step is adding a few drops of hydrogen peroxide.

If the sample turns pink , it is concerned a positive test.

This is considered a non-destructive test.  The test has the identical reactions with animal blood, so it is not possible to determine if it is animal or human blood.

Toy Applications

Phenolphthalein is used in toys as a diappering ink. The ink it is mixed with sodium hydroxide, as it reacts with the carbon dioxide in the air, it vanishes.

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Phenolphthalein Indicator Solution - 16 oz or 1 gallon
Our Price: $19.99 
Sale Price: $14.99 
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Phenolphthalein Indicator Solution - 16 oz or 1 gallon 
Water Treatment Application

One common practice is the making of closed loop corrosion inhibitors in water systems. Phenolphthalein indicators are added to the chemical make up.  When the chemical is added to the water, it naturally increases the water pH from 7 to 8 up above 10.  At this point the water will appear pink.  This can be used as a visual check to confirm the presence that the chemical is still in the water and it has not leaked out.  As fresh water is added to the system, the pH decreases, thus reducing the pH level of the water.  At this time more chemical can be add to the water system.  This eliminates the need to perform testing.

Concrete Application

The acid-base indication abilities of phenolphthalein indicators makes it very useful for testing concrete for signs of carbonation.

Concrete has naturally high pH due to the calcium hydroxide formed when Portland cement reacts with water. The pH of the water solution present in the pores of fresh concrete may be over 14.

Concrete Carbonation (Natural) will occur when the cement hydration reacts with carbon dioxide in the atmosphere (air). It can reduce the pH to 8 to 9 This reaction is usually restricted to only the surface.

When a 1.0% phenolphthalein solution is applied to normal concrete it will turn bright pink. If the concrete has under experienced carbonation, no color change will be observed.


Phenolphthalein has been used for over a 100 years as a natural laxative, but has recently has been removed for reasons of carinogenicity.

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