The difference between o-cresolphthalein and phenolphthalein

O-cresolphthalein and phenolphthalein are two common acid-base indicators, which are widely used in chemical experiments and industrial production. Although both are used for acid-base titration, there are significant differences in structure, use, and use conditions. This article will analyze the differences between o-cresolphthalein and phenolphthalein in detail from multiple angles to help readers better understand their characteristics and their application scenarios.

1. basic overview

1.1 O-Cresolphthalein Basic information

O-cresolphthalein is a colorless and transparent acid-base indicator, and its structure is composed of the o-methyl substituent of phenolphthalein. It is colorless in acidic solution, red in alkaline solution and pink in neutral solution. O-cresolphthalein has a wide range of pH discoloration and can be applied to a variety of pH titration.

11 Phenolphthalein Basic Information

Phenolphthalein is a classic acid-base indicator consisting of phenol derivatives. In acidic solution, phenolphthalein is colorless, in alkaline solution is strongly pink or red. Phenolphthalein has a narrow pH discoloration range and is usually suitable for acid-base titration with strong acidity.

2. structure and molecular composition

2.1 molecular structure of o-cresolphthalein

The molecular structure of o-cresolphthalein is sodium o-methyl -4-hydroxybenzoate, and its chemical formula is C∞NoH∞NaO₂. This structure allows o-cresolphthalein to remain colorless under acidic conditions and rapidly turn red under alkaline conditions. O-cresolphthalein has a core part of phenolphthalein in its molecule, making it a good acid-base indicator.

2.2 molecular structure of phenolphthalein

The molecular structure of phenolphthalein is sodium phenol, and the chemical formula is C≡H∞NaO₂. Due to the weak acidity of phenolphthalein, its molecular structure rapidly loses acidity under acidic conditions, and the color change range is small. The acid-base indication of phenolphthalein is stronger, but the limitation of its discoloration range makes it less useful in some cases.

3. use and scope

3.1 of o-cresolphthalein use

O-cresolphthalein is widely used in acid-base titration because of its wide pH range. It is suitable for determining the pH of strong acid and weak base and weak acid and strong base, especially in the case of weak acidic conditions, the performance of o-cresolphthalein is more prominent. o-cresolphthalein is also widely used for acid-base balance adjustment in industrial production, for example in pharmaceutical and environmental protection fields.

3.2 phenolphthalein use

Due to its narrow pH discoloration range, phenolphthalein is mainly used in acid-base titration experiments with strong acidity. For example, in determining the pH of sodium sulfate solutions, phenolphthalein is an ideal choice. Phenolphthalein is also used in some fine chemical experiments, especially where accurate pH determination is required.

4, use conditions and precautions

4.1 of o-cresolphthalein using conditions

O-cresolphthalein is usually used under appropriate experimental conditions in acid-base titration experiments. For example, the experimental environment should be kept dry to avoid contact with moisture in the air, thereby affecting the color change effect of the indicator. O-cresolphthalein may decompose under high temperature or strong light, so these conditions should be avoided when using it.

4.2 phenolphthalein use conditions

The conditions of use of phenolphthalein are similar to those of o-cresolphthalein, but attention should be paid to its narrow pH discoloration range. When using phenolphthalein, ensure that the pH of the solution is consistent with the color change range of the indicator to avoid indicator failure due to pH deviation. When using phenolphthalein should avoid mixing with other acidic or alkaline substances, so as not to affect its indication effect.

5. color change range analysis

5.1 orthocresolphthalein color change range

The color change range of o-cresolphthalein is wide, and it usually shows obvious color change between pH 8.2-10.8. In acidic solutions, the color is colorless; in alkaline solutions, the color varies from light pink to dark red. This wide range of discoloration makes it more suitable for acid-base titration.

5

Color change range of 5.2 phenolphthalein The color change range of phenolphthalein is narrow, usually between pH 8.2-10.0. In acidic solutions, the color is colorless; in alkaline solutions, the color varies from light pink to dark red. Due to the narrow range of color change, phenolphthalein is more obvious in solutions with higher pH.

6. practical application cases

6.1 ortho-cresolphthalein application case

O-cresolphthalein is widely used in acid-base titration experiments, for example, in the determination of the concentration of NaOH solution, the use of o-cresolphthalein as an indicator can easily determine the end point of titration. O-cresolphthalein is also used for acid-base balance adjustment in industrial production, for example, in the water treatment process, to monitor the pH of the solution.

6.2 phenolphthalein application case

Phenolphthalein is mainly used to determine the pH of the mixed solution of strong acid and strong alkali in acid-base titration experiments. For example, phenolphthalein may be a desirable indicator when measuring the concentration of dilute sulfuric acid. Phenolphthalein is also used in some fine chemistry experiments, for example, phenolphthalein can be used as an indicator when measuring the reducibility of the Filin reagent.

7. summary and suggestion

7.1 main differences

Through the above analysis, it can be seen that there are significant differences between o-cresolphthalein and phenolphthalein in structure, color change range, use conditions and so on. The structure of o-cresolphthalein is more complex, the color change range is wide, and it is suitable for a wide range of pH determination; while the structure of phenolphthalein is relatively simple, the color change range is narrow, and it is suitable for acid-base titration with strong acidity.

7.2 Selection Recommendations

In practical application, the appropriate indicator should be selected according to the specific requirements of the experiment. If the experiment requires a wider pH range, o-cresolphthalein can be selected; if the experiment requires a more accurate pH measurement, phenolphthalein can be selected. When using any indicator, sufficient preparations should be made in accordance with the experimental requirements to ensure the accuracy and safety of the experiment.

Through the detailed analysis of this article, we have a deeper understanding of the difference between o-cresolphthalein and phenolphthalein. Whether it is from the structure, color change range, or practical application cases, o-cresolphthalein and phenolphthalein have their unique advantages and application scenarios. In practical use, choosing the right indicator can significantly improve the accuracy and efficiency of the experiment.