Does the discoloration of the indicator occur when it encounters a substance? So no discoloration me

The indicator must have reacted when it encounters a discoloration of the substance, but no discoloration does not mean that there is no reaction.

Because the discoloration mechanism of different acid-base indicators is different, the main thing is that a chemical reaction occurs, and the structure of different conjugated systems is formed under different acidity and alkalinity, so as to develop color. For example, phenolphthalein is a conjugated double anion with a larger range of electron delocalization when the pH is greater than 9, so that the absorption wavelength enters the visible region and develops color.

However, if the substance is colorless, the color change is not visible to the naked eye, but it does react.

Acid-base indicators are a class of organic weak acids or organic weak bases with complex structures, which will partially ionize into the ions and hydrogen ions or hydroxide ions of the indicator in solution. Therefore, the acid-base indicator ionizes some ions by itself, rather than reacting with the acid-base solution. Since there is no reaction, there is no change in the properties of the solution.

Since the acid-base indicator ionizes some ions, its own structure has changed, and the reason for the change is that the acid-base indicator and the solution have undergone a chemical change because the indicator is placed in the solution. Then the outward manifestation of the change is the change in the color of the reagent. Since the acid-base indicator has different degrees of ionization in different solutions, the external performance of the reagent, that is, the color change, is different, so it will appear different colors in different solutions.

No, the indicator can only be displayed within its range, and the discoloration only means that it does not react enough to change the color of the indicator.

The discoloration just reacts, but you can't see it.

Acid-base indicator discoloration is a chemical change. A commonly used indicator is an organic weak acid indicator that changes color when exposed to acid or alkali is the use of the principle of chemical equilibrium movement. The principle of action of acid-base indicator is generally some organic weak acid or weak base, or organic acid-base amphoteric substances, which can also participate in the proton transfer reaction in the acid-base titration process, and the change of their own color is caused by the change of molecular structure, and the color is reversible with the transformation of the structure.

For example, phenolphthalein, methyl orange.

Classification of acid-base indicators:1.Nitrophenols are a class of acidic indicators, such as p-nitrophenols.

2.Phenolphthalein includes phenolphthalein, thyme phenolphthalein and naphthalenophthalein, etc., which are all organic weak acids.

3.Sulfophenylphthaleins include phenol red, cresol red, bromophenol blue, thymol blue, etc., which are all organic weak acids.

4.Azo compounds include methyl orange, neutral red, etc., which are amphoteric indicators, which can be used for acid dissociation and basic dissociation.

The above content refers to: Encyclopedia - acid-base indicator.

If in an acidic solution, due to the increase of C(H+), according to the principle of equilibrium shift, it can be seen that the equilibrium will move in the direction of the reverse reaction, so that C(Hin) increases, so it is mainly red (acidic). If in an alkaline solution, due to the increase of C(OH-), OH- combines with H+ generated by Hin ionization to form H2O, which is more difficult to ionize, so that the ionization equilibrium of litmus shifts in the direction of positive reaction, so C(IN-) increases, so it is mainly blue (alkaline). If c(hin) and c(in-) are equal, it appears purple.

In practice, it is difficult to accurately observe the slight changes in the color of the indicator discoloration point with the naked eye. The process of visually changing an acid-base indicator from one color to another can only occur within a certain pH range, i.e., the change in color can only be barely discerned when one color corresponds to ten times the concentration of the other. At the same time as this color change, the pH value of the medium hydrogen sterilization biological indicator changes from one value to another.

When the pH of the solution is greater than pkhin, [in-] will be greater than [hin] and when [in-] [hin]=10, the solution will completely take on the color of the basic component, while the acid color is masked, then the pH of the solution = pkhin+1. In the same way, when the pH of the solution is less than pkhin, [in-] will be less than [hin] and when [in-] [hin]=1 10, the solution will completely take on the color of the acidic component, while the alkaline color is masked, then the pH of the solution = pkhin-1.

The color of the visible solution varies from pH=PKHin-1 to pH=PKHin+1, which is called the color change range of the indicator, i.e., the color change domain. In the discoloration range, when the pH of the solution changes, the ratio of the basic and acid components changes, and the color of the indicator also changes. Outside of this range, such as ph pkhin+1, all you see is a basic color; At pH PKHin-1, you will only see an acid color.

Therefore, the discoloration of the indicator ranges from about 2 PH units. Due to the different sensitivity of human vision to various colors, and the mixed colors of the indicators in the color change domain, the two colors affect each other, so the actual observation results are different from the theoretical values, and the color change range of most indicators is less than 2 PH units. The answer comes from:

Indicator discoloration is a chemical change.

Indicators are a class of chemical reagents. Under certain medium conditions, its color can change, turbidity or precipitation, and fluorescence. It is often used to test the acidity and alkalinity of a solution.

It is used in titration analysis to indicate the titration endpoint; Detection of hazardous substances in environmental testing. It is generally divided into acid-base indicators.

Redox indicators, metal indicators, adsorption indicators, etc.

The reagent used to indicate the end point of the titration. In the process of various titrations, with the addition of titrant, the concentration of the titrated substance and the titrant are constantly changing, and the ion concentration will change greatly near the equivalence point, and the reagent that can display the change in the ion concentration (such as changing the color of the solution, generating precipitation, etc.) is called an indicator.

If the titrant or the substance being titrated is colored, they themselves act as an indicator, such as potassium permanganate.

Different indicators exhibit different colors in different acid-base environments.

Chemical changes. 1. The principle of action of the indicator 1. Acid-base indicator: generally some organic weak acids or weak bases, or organic acid-base amphoteric substances, they can also participate in the proton transfer reaction in the acid-base titration process, and the change of their own color is caused by the change of molecular structure, and the color is reversible with the transformation of the structure.

For example, phenolphthalein, methyl orange. 2. Classification: Monochrome indicator:

Only one type of acid or base form has a color indicator. Such as phenolphthalein two-color indicator: acid or basic type has color indicator.

Such as methyl orange.

It is a chemical change, the acid-base indicator is usually a weak organic acid or organic base, their acid structure has a different color from its conjugated base structure, when the pH value of the solution changes, the acid structure of the indicator changes between the base structure, which causes a change in color.

Chemical changes, acid-base indicators are generally weak acids, adding acid is to inhibit ionization, adding alkali is to promote ionization, according to the relative change of the amount of its ions and the amount of the original substance molecules, resulting in different colors.

Chemical changes. The indicator is a weak organic acid or organic base, and the ions ionized in solution have a special color.

Acid-base indicator. Indicates the change in the concentration of H+ in the solution and is an organic weak acid or organic weak base, which has different colors for acidity and alkalinity. The dissociation constant of the indicator acid Hin in the solution is Ka[H+[in-hin, that is, the color of the solution is determined by [in-hin, which in turn is determined by [H+.

Take methyl orange (Ka as an example, when the pH of the solution is pH, it is acidic and red; pH, alkaline and yellowish; In addition, a mixture of red and yellow orange appears, which is called the discoloration range of the indicator. Different acid-base indicators have different discoloration ranges.

Metal indicators. Most of the indicators used in complexation titration are dyes, which can be complexed with metal ions at a certain pH to show a completely different color from the free indicator and indicate the end point.

Redox indicators. It is an oxidizing agent or reducing agent, and its oxidation form has a different color from the reduced form, and when it is oxidized (or reduced) in the titration, it changes color, indicating a change in the potential of the solution.

Precipitation titration indicator. It is mainly the titration of AG+ and halogen ions, with potassium chromate, ammonium iron or fluorescent yellow as indicators.

To put it simply, it looks like this.

The indicator itself has one color, and when it reacts with an acid or base, it produces another substance, which has another color.

It is to touch the acid and alkali to show different colors.

It is also acid-base neutralized.

It is a temporary change in the properties of matter.

Acid-base indicator discoloration is a chemical change.

Acid-base indicators are in fact organic weak acids or organic weak bases, they can be partially ionized into the ions and hydrogen ions (or hydroxide ions) of the indicator in the solution, when they encounter hydrogen ions in acidic solutions or hydroxide ions in alkaline solutions, they will undergo structural changes, their molecules and ions have different colors, so they show different colors in solutions with different pH.

Therefore, the discoloration of the acid-base indicator is caused by the chemical reaction between the hydrogen ions or hydroxide ions in the solution and the indicator.

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Acid-base indicator discoloration is a chemical change.

It is a chemical change, the acid-base indicator is usually a weak organic acid or organic base, their acid structure has a different color from its conjugated base structure, when the pH value of the solution changes, the acid structure of the indicator changes between the base structure, which causes a change in color.

When the acid-base indicator changes color, a chemical reaction occurs, which is a chemical change.

It is a chemical change The commonly used indicator is an organic weak acid indicator, and the discoloration of the indicator when exposed to acid or alkali is the use of the principle of chemical equilibrium movement 1. The principle of action of the indicator 1. Acid-base indicator: generally some organic weak acid or weak base, or organic acid-base amphoteric substances, they can also participate in the proton transfer reaction in the acid-base titration process, and the change of their own color is caused by the change of molecular structure, and the color is reversible with the transformation of the structure. For example, phenolphthalein, methyl orange.

2. Classification: Monochrome indicator: There is only one type of color indicator in the acid or basic type.

Such as phenolphthalein two-color indicator: acid or basic type has color indicator. Such as methyl orange.

2. The pH range of indicator discoloration: 1. The principle of discoloration: Hin indicates the indicator Hin = H+ +IN- IN-

In fact, the discoloration range of the indicator is obtained according to ().

a.Observation with the human eye.

b.Compare titrations.

c.Theoretical discoloration point calculation.

d.Titration of the experience ridge roll.

Correct answer to the case of slag: a