Purple litmus is a commonly used acid-base indicator, and its main ingredient is litactic acid. When the pH of the solution changes, the color of the purple litmus also changes. Let's take a closer look at what color purple litmus shows when it meets acid and alkali.
1. Purple litmus meets acidic solution
When purple litmus encounters an acidic solution, the following reaction occurs:
h+ +acid red ⇌ colorless
Among them, H+ represents hydrogen ions, acid red represents the red part of litmus, and colorless represents colorless. This reaction is an acid-base neutralization reaction in which hydrogen ions in an acidic solution combine with the red part of litactylic acid to form a colorless compound. As the concentration of the acidic solution increases, the red part of the litmus is gradually neutralized, and the color of the litmus gradually changes from red to yellow and finally to orange. Therefore, when purple litmus encounters an acidic solution, its color gradually changes from red to yellow or orange.
2. Purple litmus meets alkaline solution
When purple litmus encounters an alkaline solution, the following reaction occurs:
oh- +base blue ⇌ colorless
Among them, oh- represents hydroxide ions, base blue represents the blue part of litmus, and colorless represents colorless. This reaction is also an acid-base neutralization reaction, in which the hydroxide ions in the alkaline solution combine with the blue part of the litmus to form a colorless compound. As the concentration of the alkaline solution increases, the blue part of the litmus is gradually neutralized, and the color of litmus gradually changes from blue to green and finally to yellow. Therefore, when purple litmus encounters an alkaline solution, its color gradually changes from blue to green or yellow.
3. The color change law of purple litmus
According to the above reaction, we can derive the law of color change of purple litmus:
1.Acidic solution: As the concentration of the acidic solution increases, the color of the litmus gradually changes from red to yellow or orange.
2.Alkaline solution: As the concentration of the alkaline solution increases, the color of litmus gradually changes from blue to green or yellow.
3.Neutral solution: In a neutral solution, litmus is purple in color.
Fourth, the application of purple litmus
As a commonly used acid-base indicator, purple litmus is widely used in laboratories, industrial production and life. Here are some common applications:
1.It is used in the laboratory to test the acidity and alkalinity of the solutionBy observing the color change of purple litmus, the acidity and alkalinity of the solution can be judged. For example, when a purple litmus encounters an acidic solution, its color gradually changes from red to yellow or orange;When an alkaline solution is encountered, its color gradually changes from blue to green or yellow.
2.It is used in industrial production to monitor pH:In many industrial processes, pH monitoring and control are required. Purple litmus can be used as a simple and quick indicator to help the operator determine the pH level.
3.It is used to detect the acidity and alkalinity of food in lifeThe acidity and alkalinity of food has a great impact on human health. By using purple litmus to detect the acidity and alkalinity of food, it can help people understand the properties of food so that they can choose the right food.
4.Used in Education for Teaching Presentations:The color change process of purple litmus is intuitive and obvious, making it ideal for teaching demonstrations. By observing the color changes of purple litmus, students can more intuitively understand the principle of acid-base neutralization reaction.
Purple litmus exhibits different colors when exposed to acids and bases, a property that makes it a very useful acid-base indicator. By observing the color change of purple litmus, we can judge the acidity and alkalinity of the solution, which can be used in various occasions in laboratories, industrial production and life.
5. Precautions
When using purple litmus as an acid-base indicator, the following points need to be noted:
1.Choose purple litmus with higher purity:In order to ensure the accuracy of the experimental results, purple litmus with high purity should be selected. In addition, care should be taken to avoid exposing purple litmus to strong light, high temperatures, or high humidity to avoid affecting its performance.
2.Pay attention to the operation method:When performing experiments with purple litmus, they should be performed in accordance with the prescribed method of operation. For example, when adding acidic or alkaline solutions dropwise, the drops should be added slowly to avoid spilling the solution;When observing the color change, the purple litmus should be placed on a white background for a clearer view of the color change.
3.Pay attention to experimental safety:When conducting experiments, attention should be paid to experimental safety. For example, when working with highly corrosive acidic or alkaline solutions, protective eyewear and gloves should be wornWhen disposing of waste liquid, it should be treated in accordance with relevant regulations to avoid polluting the environment.
4.Pay attention to the experimental conditions:The color change of purple litmus was greatly affected by the experimental conditions. For example, factors such as temperature, pressure, solvents, etc., can all affect the color change of purple litmus. Therefore, when conducting experiments, the stability of experimental conditions should be maintained as much as possible.
5.Note the distinction from other indicators:In addition to purple litmus, there are many other acid-base indicators. When using these indicators, attention should be paid to the difference from purple litmus to avoid misjudgments. For example, phenolphthalein is red in acidic solutions and colorless in alkaline solutions;Phenolphthalein is red in alkaline solutions and colorless in acidic solutions. Therefore, when using these indicators, appropriate experimental conditions should be selected according to their characteristics.
When using purple litmus as an acid-base indicator, attention should be paid to choosing purple litmus with higher purity, following the operation method, paying attention to experimental safety, maintaining the stability of experimental conditions, and distinguishing it from other indicators. Through the above precautions, the accuracy and safety of the experimental results can be guaranteed.