The key difference between bromocresol blue and bromocresol purple is that the colour change for bromocresol blue is yellow (acidic colour) to green (neutral) to blue (basic colour) while the colour change for bromocresol purple is yellow (acidic colour) to violet (basic colour).
There are several compounds that we use to check the acidity or basicity levels of solutions. In fact, all solutions have a pH value from 0 to 14; we call it their pH value. Usually, we consider the solutions with pH values less than 7 as acidic while those are having a pH value of more than 7 are basic solutions. Whereas, a solution with pH value 7 is a neutral solution. Moreover, the compounds that we use to check the pH values of solutions are the pH indicators. Bromocresol Blue and Bromocresol Purple are two very good pH indicators that are useful in biology and analytical chemistry. Though they perform the same basic function, there are some difference between Bromocresol Blue and Bromocresol Purple, which we will be discussing in this article.
CONTENTS
1. Overview and Key Difference
2. What is Bromocresol Blue
3. What is Bromocresol Purple
4. Side by Side Comparison – Bromocresol Blue vs Bromocresol Purple in Tabular Form
5. Summary
What is Bromocresol Blue?
Bromocresol Blue is a greenish violet powder with no odour. It is a non-flammable solid. And, if someone consumes it, he must be given 1-2 cups of milk to induce vomiting. Also, when we heat it to decompose, it gives out acrid fumes. It is not hazardous, but we should use it with caution.
Thus, if Bromocresol blue goes inside the eye, the person must wash eyes under water for some time to wash it away. It is an indicator that we use in acid-base titrations where a weak base is titrated against a weak acid. The indicator is yellow at pH less than 6 and blue at pH more than 7.6. It turns green at pH 7 which is the neutralization pH of a weak acid/base solution.
What is Bromocresol Purple?
It is a pH indicator and important as a dye as well. In summary, the acidic colour of this indicator is yellow and the basic colour is violet. In other words, this indicator turns yellow at pH values below 5.2 and turns violet at pH values above 6.8. usually, we prepare it as a 0.04% aqueous solution. Mainly, we use it in medical laboratories. That is to measure the albumin content in samples. There are some other applications as well; we can use it in the microbiological laboratory to stain dead cells and to assay lactic acid bacteria. This indicator is available as a purple coloured powder.
Figure 01: Chemical Structure of Bromocresol Purple
This compound is a sodium salt. If it goes into eyes accidentally, one must wash eyes with excess water for 15 minutes lifting upper and lower eyelid frequently. If someone consumes the compound, poison control has to be called immediately. When inhaled, fresh air will bring back normal breathing. It is a non-flammable solid that emits acrid fumes when heated to decomposition. Bromocresol purple must be stored with proper ventilation.
What is the Difference between Bromocresol Blue and Bromocresol Purple?
Bromocresol blue is a greenish violet powder with no odour whereas bromocresol purple is a pH indicator and important as a dye as well. Bromocresol purple appears as a purple coloured powder. The colour change for bromocresol blue is yellow (acidic colour) to green (neutral) to blue (basic colour) while the colour change for bromocresol purple is yellow (acidic colour) to violet (basic colour). This is the key difference between bromocresol blue and bromocresol purple. Furthermore, another difference between bromocresol blue and bromocresol purple is that the bromocresol blue gives the colour changes at the pH range of 6 to 7.6 whereas the colour changes of bromocresol purple occur at 5.2 to 6.8 pH range.
More facts about the difference between bromocresol blue and bromocresol purple are given in below infographic.
Summary – Bromocresol Blue vs Bromocresol Purple
Bromocresol blue and bromocresol purple are important pH indicators. The key difference between bromocresol blue and bromocresol purple is that the colour change for bromocresol blue is yellow (acidic colour) to green (neutral) to blue (basic colour) while the colour change for bromocresol purple is yellow (acidic colour) to violet (basic colour).
Reference:
1. “Bromocresol Purple.” Wikipedia, Wikimedia Foundation, 12 June 2018. Available here
2. “Bromocresol Purple 114375.” Sigma-Aldrich. Available here
Image Courtesy:
1.”Structure of Bromocresol purple” By LHcheM – Own work, (CC BY-SA 3.0) via Commons Wikimedia