Junior Chemistry Does manganese dioxide participate in the reaction process as a catalyst? It s a re

In the definition of catalyst, it is said that a substance that can change the chemical reaction rate of other substances in a chemical reaction, but its mass and chemical properties have not changed before and after the reaction is called a catalyst.

According to this definition, you can look at the mass and chemical properties of manganese dioxide before and after the reaction, and if it meets the definition, it is a catalyst.

Sometimes, the catalyst does not participate in the reaction, the catalyst first reacts with one of the reactants, and then the products of the two continue to carry out new chemical reactions under the original conditions, and the reaction conditions of the products of the catalyst reaction are changed compared with the reaction conditions of the original reactants. The substances that were originally formed by the chemical reaction of the catalyst will be regenerated into the original catalyst in a further reaction, i.e., the mass and chemical properties mentioned above have not changed before and after the reaction.

So, to put it simply, it is the definition in our junior high school book, and what has not changed is considered a catalyst, and there is no need to study how it reacts.

It is just a catalyst and does not react with reactants.

In fact, participated, only in the end manganese dioxide was regenerated.

The catalyst participates in the reaction, but it goes through two different reactions and becomes the original again, and the reactants become products through these two reactions, which is the essence of catalysis, so the chemical properties of the catalyst remain unchanged before and after the reaction, but some physical properties such as shape will change.

Of course, manganese dioxide participates in the reaction, but not only is it consumed in the reaction, but also as much manganese dioxide is generated.

So I told you about it as a catalyst in junior high school chemistry, and then the chemistry major in college will tell you about the specific form, and now you just need to know that there is such a thing.

There's a saying that participation is just generated again, and it seems like it's boundless, and the mechanics are complicated.

Experiment 1 Observe hydrogen peroxide at room temperature in a test tube.

solution, slowly releasing small bubbles.

Experiment 2 Weigh a certain mass of manganese dioxide.

And observe that the gas that does not rekindle the wooden strip with sparks cannot be released.

Experiment 3 A certain mass of manganese dioxide was added to the sodium peroxide in the above test tube.

solution and go deep into a strip of wood with Mars. The re-ignition of the wood strips was found, which proved that the waxed manganese dioxide accelerated the decomposition of hydrogen peroxide. After the reaction was stopped, the hydrogen peroxide solution was added, and it was found that oxygen could be released quickly, proving that the properties of manganese dioxide remained unchanged.

Experiment 4 After the experiment, the solids were filtered, dried and weighed, and the quality was found to be unchanged.

In this way, manganese dioxide changes the reaction rate of hydrogen peroxide, and its chemical properties and mass remain unchanged. It was proved that manganese dioxide is a catalyst for hydrogen peroxide.

【Conjecture】The characteristic of the catalyst is "one change, two unchanged", that is, the reaction rate changes, the mass and chemical properties do not change

Experiment] (1) Copper oxide has a catalytic effect on the decomposition of hydrogen peroxide, which can accelerate its decomposition rate and the rate of oxygen generation, so the phenomenon in the step is that there are bubbles and the wood strip with sparks rekindles; The characteristic of the catalyst is "one change, two unchanged", and its mass remains unchanged before and after the reaction, so the mass of copper oxide weighed in the step is still ; The characteristic of the catalyst is "one change, two unchanged", in which the reaction rate changes, here it accelerates, so the phenomenon is that there are bubbles released in the solution, and the wooden strip with sparks rekindles

2) In order to see whether copper oxide can change the rate of reaction, it is necessary to compare the phenomenon of adding copper oxide with no copper oxide to draw scientific and reasonable conclusions

3) The instruments used in filtration are: iron frame (with iron ring), funnel, beaker, glass rod, the last one is missing, and its function is drainage

4) Hydrogen peroxide is decomposed under the catalytic action of copper oxide to produce water and oxygen, and its literal expression is: copper hydrogen peroxide.

Water + Oxygen Expansion] In this reaction, copper oxide changes the decomposition rate of hydrogen peroxide, while its own mass and chemical properties do not change, so it can be known that the three conditions that can be used as a catalyst are: changing the reaction rate of other substances while its own chemical properties and mass remain unchanged before and after the reaction

Therefore, the answer is: [conjecture] that the mass and chemical properties remain unchanged

Experiment] (1) Step Phenomenon.

Step 1 Result.

Step phenomenon.

Conclusion There are bubbles to produce the re-ignition of wooden strips with sparks.

The mass of copper oxide that is weighed is still .

There are bubbles in the solution that emit a rekindling of the wooden strip with sparks.

The conjecture is not valid; The conjecture is valid

2) Compare with steps

3) glass rods; Drainage

4) Copper hydroxide peroxide.

Water + Oxygen Expansion] changes the reaction rate of other substances, while its own chemical properties and mass remain unchanged before and after the reaction

(1) The decomposition of hydrogen peroxide solution at room temperature is very slow, and the phenomenon seen in the experiment is that the wooden strip with sparks does not rekindle;

2) Changing the temperature can accelerate the decomposition rate of hydrogen peroxide, and heating can accelerate the decomposition rate of hydrogen peroxide, and the wood strips with sparks will rekindle;

3) Manganese dioxide can accelerate the decomposition rate of hydrogen peroxide, and the phenomenon is that there are bubbles and the wood strips with sparks rekindle;

4) Hydrogen peroxide was added again, and bubbles were found, indicating that the chemical properties of manganese dioxide remained unchanged in this process;

5) After the experiment is completed, the manganese dioxide in the test tube is filtered, washed, dried and weighed, and its mass is found to be equal to that before the reaction

Answer: (1) The wooden strip with sparks does not rekindle The hydrogen peroxide solution decomposes slowly at room temperature.

2) There are bubbles generated, and the sparkled strips of wood are re-ignited Heating can accelerate the rate of hydrogen peroxide decomposition.

3) There are bubbles generated, and the wood strips with sparks rekindle Manganese dioxide can accelerate the decomposition rate of hydrogen peroxide.

4) There are bubbles that are produced unchanged.

5) Equal.

Catalysts

catalyst

A substance that can significantly increase the reaction rate, and its own chemical properties and quantities remain unchanged before and after the reaction.

Characteristic. Before and after the reaction, although the chemical properties remain unchanged, some physical properties change due to participation in the reaction.

It has the same catalytic effect on the forward and reverse reactions, so it can only shorten the time to reach equilibrium, but cannot change the equilibrium composition of the system.

There is a special selectivity, and a certain type of reaction can only be catalyzed by certain catalysts.

Small amounts of impurities in the catalyst or reaction system can often strongly affect the performance of the catalyst. Some substances themselves have no catalytic effect, but when added to the catalyst, they can greatly improve the activity of the catalyst, which is called a co-catalyst. There are also some substances, which can greatly reduce or even eliminate the catalytic effect of the catalyst by adding a small amount, and are called poisons (or inhibitors).

Class. Metal catalysts. It mainly refers to certain transition metals of the cycle, such as iron, gold, platinum, palladium, rhodium, iridium, etc., as well as alloys of certain transition metals, which can be used for dehydrogenation and hydrogenation reactions, and some also have catalytic activities for oxidation and reforming.

Semiconductor catalysts. It is mainly the oxides of various non-stoichiometric transition metals, such as ZNO, Nio, V2O5, Fe2O3, Cr2O3, MoO3, etc., which can accelerate the oxidation, hydrogenation, dehydrogenation and other reactions with electron transfer. Practical semiconductor catalysts are often multi-component oxide complexes, which are complex in composition and have many influencing factors.

Acid and alkali catalysts. The catalytic effects of Arrhenius acid-base, Brunsti acid-base, and Lewis acid-base are all acid-base catalysis. Acid-base catalysis can be divided into two categories: homogeneous and multiphase.

Homogeneous acid-base catalysis is generally carried out by an ionic mechanism. Some reactions with proton transfer, such as hydration and dehydration, esterification and hydrolysis, alkylation and dealkylation, etc., can often be catalyzed by homogeneous acid-base. Multiphase acid-base catalysts are mainly solid acid-bases, among which the most widely used are solid oxide acid-base catalysts, which are used to catalyze the following reactions:

Dehydration and hydration, isomerization, cracking, alkylation, polymerization, hydrogen transfer, etc. Alumina, aluminum silicate, and molecular sieve are the three most important types of solid acid catalysts.

Coordination (complexing) catalysts. Generally inorganic or organic complexes of transition metals. During the reaction, the catalyst and the reaction group form coordination bonds to form intermediate complexes, which activate the reaction molecules.

Coordination (complexing) catalysts are generally used in homogeneous catalytic reactions, which can catalyze hydrodehydrogenation, oxidation, isomerization, hydration, carbonyl synthesis, polymerization and other reactions. In recent years, low-molecular-weight complexes with high catalytic activity have been combined with polymers to make supported polymer catalysts, which not only retain the advantages of homogeneous complexation catalytic activity and high selectivity, but also overcome the shortcomings of catalysts such as difficult separation and instability.

Enzyme catalysts. The various complex reactions that take place in living organisms are basically enzyme-catalyzed reactions. The enzyme itself is a protein molecule, a macromolecule between 3,100 nanometers in size that is polymerized by amino acids in a certain order.

Enzyme catalysts are highly selective, have very high catalytic efficiency, and have mild reaction conditions.

The second equation is followed by a gas symbol.

It is not difficult to see that the product of manganese dioxide decomposes after the reaction with hydrogen peroxide, so from a macroscopic point of view, the mass of manganese dioxide remains unchanged, and hydrogen peroxide is decomposed into water and oxygen, but in fact, manganese dioxide is catalyzed by participating in the reaction.

MNO2 is involved in the reaction, but after the reaction it is replaced by other substances.

Hydrogen peroxide is catalyzed by manganese dioxide to produce water and oxygen, and the chemical equation for anti-starvation is 2H2O2

mn o 2

2H2O+O2 Tung limb matching

Therefore, the respondent pointed out that the case was: 2h 2 o 2

mn o 2

2h 2 o+o 2 ↑．4,

No. Catalysts are selective.

There are two mechanisms of catalysts:

1. The catalyst participates in the reaction during the reaction and is reduced to the original components after the reaction is completed. For example, potassium manganate is added when pyrolysis of potassium permanganate.

In the decomposition process of potassium permanganate, potassium manganate is involved in the reaction, and the specific way is unclear. Finally, it appears as potassium manganate. The morphology of the catalyst changes before and after the reaction, the particles become powder, the powder becomes granules, and so on.

2. The catalyst does not participate in the reaction, such as in the platinum-rhodium alloy network, nitrogen and hydrogen react to form ammonia. The platinum-rhodium alloy mesh provides electrons during the reaction (or a similar effect, the details are not clear, but it does not react itself), and the morphology of the platinum-rhodium alloy mesh does not change before and after the reaction.

Manganese dioxide can be used as a catalyst for hydrogen peroxide splitting, a catalyst for potassium chlorate to chlorine gas, and so on.

Digital application in manganese dioxide as a catalyst experiment (very good)**.

(1) Add 5ml to the tube

5 of the hydrogen peroxide solution, put a small wooden strip with sparks into the tube. Phenomenon: A small amount of bubbles emerges, and the wooden strip does not rekindle.

2) Add a small amount of manganese dioxide to the above test tube and extend a small wooden strip with sparks into the test tube. Phenomenon: A large number of bubbles and water vapor are generated, small wooden strips are re-ignited, and the quality of manganese dioxide remains unchanged after re-measurement.

Conclusion: A large number of bubbles generated are oxygen. Manganese dioxide can accelerate the decomposition of oxygen by hydrogen peroxide without changing its own amount, and is used as a catalyst.

By identifying the products as water and oxygen, it was proved that manganese dioxide was not involved in the reaction. 2. By weighing, it is determined that the manganese dioxide has not changed before and after the reaction. 3. The hydrogen peroxide without manganese dioxide and manganese dioxide was decomposed separately, and the reaction rate was compared, and the hydrogen peroxide with manganese dioxide was quickly decomposed.

Manganese dioxide, chemical experiment demonstration, manganese dioxide catalyzes hydrogen peroxide decomposition.