Why can t SO2 fade purple litmus? Why does it not change when it turns red?

Sulfur dioxide is dissolved in water to form sulfurous acid, which ionizes hydrogen ions, making the solution acidic, so the purple litmus turns red. What you are talking about is the bleaching properties of sulfur dioxide. At the high school level, bleaching is only applied to magenta solutions.

First of all, you need to understand why sulfur dioxide can fade magenta. This is because sulfur dioxide can bind to the organic molecules in magenta, changing its structure and fading it. After heating, the sulfur dioxide is separated from it and the sulfur dioxide is newly generated.

Therefore, it can turn red. This is not the case with litmus. Of course, sulfur dioxide can also fade the purple acidic potassium permanganate, not because of bleaching, but because the sulfur dioxide is oxidized, the structure changes, and no matter how heated it is, it will not return to its original color.

The bleaching effect of SO2 is achieved by unstable compounding.

That is to say, SO2 bleached magenta is a colorless soluble compound formed by SO2 and magenta, which has poor thermal stability, so it is easy to decompose when heated, that is, a slight heat can restore the color of the magenta solution.

The chemical essence of litmus is that it is an organic acid that does not combine with SO2, so SO2 cannot fade litmus.

The reddening is due to the fact that SO2 dissolves in water to form an acidic solution, which makes the purple litmus solution red.

No, SO2 is a colored substance, and the fading is combined with the colored substance.

This must be a colored substance with a specific structure.

The common ones are magenta, etc.

But litmus does not, so SO2 and H2O react to form H2SO3, which is acidic.

It only makes the purple litmus red.

The first year of high school students knew that SO2 could fade the magenta reagent.

The red color of the purple litmus is due to the fact that SO2 dissolves in water to form sulfurous acid, which is acidic.

You may not have figured it out, or you may have never made it clear. Said that he could fade the solution, but it could react with magenta and fade magenta, and I hadn't heard of anything else in high school. After all, SO2 makes the acidic oxide, of course, react with water to form an acid, making the litmus solution red.

The chemical essence of purple litmus is that it is an organic acid that does not combine with SO2, so SO2 cannot fade litmus.

Cause: Sulfur dioxide has a bleaching effect. The bleaching principle of SO2 is that SO2 reacts with the bleached substance to form a colorless unstable compound, and if it is destroyed, it will blind the paraquinone formula that plays the role of the color of the bleached substance, but litmus does not have this structure.

From the point of view of acidity and alkalinity, sulfur dioxide and water produce sulfurous acid, which should make the purple litmus solution red.

Chemical equation: SO2 + H2O = H2SO3.

No, sulfur dioxide reacts with water to form sulfurous acid, which is a moderately strong acid, so it is acidic, which will make the purple litmus solution red.

Litmus is a weak organic mind-touching acid, which changes its conjugated structure and changes color under the different effects of acid-base solutions. As a result, sulfur dioxide turns litmus red, showing acidity; Sulfur dioxide fades the magenta, which is bleaching and the product is unstable, and the magenta returns to its original color after heating.

The normal litmus reagent is purple, it turns from purple to red when it encounters acid, and from purple to blue when it encounters alkali, which is why it is called an acid-base indicator.

The principle of SO2 bleaching is that it is related to:

Organic colors. The reaction produces a colorless substance, and no redox reaction occurs. This reaction is unstable, and when heated, it will decompose, and the organic pigment will also appear, which is the principle of magenta solution fading. But SO2

will not be associated with colored inorganic substances.

Such a reaction occurs. The litmus reagent is inorganic, so SO2 will not fade it.

Since SO2 is soluble in water to form sulfurous acid, it is acidic, so it can make the litmus reagent red.

To fade the litmus reagent, you can add strong oxidizing substances, such as ozone, ozone can fade almost all these colored substances, but what happens at this time is a redox reaction, not bleaching.

No. SO2 makes purple litmus red, making it acidic.

Some color-developing functional groups can be combined with SO2 and become colorless. The color of litmus is not due to this group, so it can't.

Sulfur dioxide cannot fade litmus.

Sulfur dioxide is dissolved in water to form sulfite, which undergoes the following changes under the action of acids or bases: their conjugated system is changed, but not destroyed. Different conjugated systems exhibit different colors.

In this critical structure, bisulfite ions are "out of their hands" and cannot destroy their conjugated system, but sulfur dioxide hydrates can provide hydrogen ions that turn the conjugated system red.

The presence of the conjugated system causes the single and double bonds to tend to assimilate, and the energy required for the electronic transition of the bond is also reduced. The larger the conjugated structure, the more obvious this phenomenon becomes, and when the absorbed photon energy is reduced to a certain level, it falls into the wavelength range of visible light, and the matter is able to show color.

After sulfur dioxide gas is introduced, it will react with the water in the test solution to form sulfurous acid, and the purple litmus test solution will be red when it encounters acid. As for the non-fading, because the sulfurous acid can be oxidized into sulfuric acid in the air, the solution is still an acid solution after placement, and the sulfur dioxide here reflects the nature of its acidic gas, and does not reflect bleaching, which is an irreversible process, so it does not fade.

Litmus (the main component is represented by HL) can be ionized in aqueous solution as follows: HL red H+L-blue.

In acidic solutions, red molecules are the main form of existence, and the solution appears red; In alkaline solutions, the ionization equilibrium shifts to the right, and blue ions are the main form of existence, and the solution appears blue; In a neutral solution, red molecules and blue acid ions exist at the same time, so the solution appears purple.

Sulfur dioxide has bleaching properties, and the principle of its bleaching effect is that sulfur dioxide reacts with the addition and combination of colored substances to form colorless substances. It can bleach not only magenta, but also other organic pigments. For example, yellow wheat straw will turn white when it is bleached with sulfur dioxide, and straw hats woven from wheat straw are bleached with sulfur dioxide.

However, sulfur dioxide is unstable with the colorless substance formed by organic pigments. It will decompose after a long time, so the straw hat will turn yellow after a period of time, and sulfur dioxide cannot bleach colored inorganic substances.

The litmus solution is characterized by turning red when acidic and blue when alkaline. Sulfur dioxide is an acidic oxide that produces sulfurous acid when exposed to water, and then turns red when it encounters litmus, at this time, it is the nature of sulfuric acid dioxide oxide rather than bleaching.

Sulfur dioxide is a substance that can be tolerated in water, and when dissolved in water, it forms acid, which changes, and it is acid that makes litmus red, so it is not sulfur dioxide.

SO2 is characteristic bleaching, can make the magenta fade, and return to red after heating, but can not make the acid-base indicator fade, it is acidic, so that the litmus turns red, to distinguish the bleaching of SO2 and chlorine water is not the same, chlorine water is permanent bleaching, can make the acid-base indicator first turn red and then fade, and SO2 is reversible bleaching.

Hope it helps.

Sulfur dioxide is an acidic oxide, which produces sulfurous acid when exposed to water, while the phenolphthalein test solution turns red when exposed to alkaline substances, and the acidic substances do not change color (still colorless), and the litmus solution turns blue when alkaline, and the acidic turns red.

High School Fading Mechanism:

There is a kind called adduction. Specifically refers to SO2, which has an addition reaction with organic chromogen, but is reversible, and will recover under reheating and other conditions, and high SO2 only bleaches magenta, not bleaching acid-base indicator.

Cl2 and SO2 discolor magenta solutions on a different principle.

The bleaching principle of Cl2 is: chlorine gas reacts with water to produce hydrochloric acid and hypochlorous acid Cl2 H2O === HCL HCL Hypochlorous acid decomposes oxygen (primary oxygen).

2hclo === 2hcl ＋ o2↑

This primary oxygen has strong oxidizing properties, oxidizing magenta into a colorless substance, causing the magenta solution to fade, and this fading is irreversible.

The bleaching principle of SO2 is: SO2 is synthesized into H2SO3 by hydration, and H2SO3 undergoes an addition reaction with magenta to form an unstable colorless compound, which fades the magenta solution. This reaction is reversible, and under heating conditions, the colorless compounds will decompose the finished red and H2SO3, which in turn will decompose into SO2 and H2O