A few chemistry questions in the third year of junior high school, play well to increase points, and

1 Because most of the soluble substances will be soluble in water, i.e., water can dissolve most of the soluble substances, and when there are solutes, the solvent, i.e., water, should also be present. Because life needs water, the presence of water proves the existence of conditions for life, which makes sense for the search for life on Mars.

2 Oxygen is derived from photosynthesis by green plants.

1) There are soluble salts in places where the temperature is very high, which proves that when the water has not evaporated,,。 The soluble salts may be due to the high temperature on the surface of Mars, which evaporates the water...

That is, there is water in the ground, water dissolves the soluble salts in the ground, the soluble salts rise to the surface, and the water is evaporated at the high temperature of the surface, leaving solid salts on the surface.

The meaning is to find life.

2) Mainly photosynthesis.

Before the emergence of plants, there was almost no oxygen in the Earth's atmosphere. Mainly methane, carbon dioxide, water vapor. This ratio has been maintained for more than 300 million years. It wasn't until a billion years after the advent of plants that oxygen accounted for 1 5 percent of the atmosphere

x*5%+y*20%=100*10%

x+y=100

x+y=100

x<=80,y<=50)

x+y=100

x=200/3

y=100/3

100g of 10% sucrose solution can be obtained by mixing 200 3g of 5% sucrose solution and 100 3g of 20% sucrose solution.

1. No, the reason is very simple, explain: carbon dioxide and water vapor are generated after combustion, which volatilize into the air, and the mass is actually not reduced, of course, for candles, it must be reduced. Just like when you eat, if you eat one bite, you will lose one bite of food!

2. Magnesium is burned in the air to produce magnesium oxide, you can see according to the chemical formula, the magnesium element is not reduced, on the contrary, the oxygen element is increased, according to the mass conservation of the chemical reaction, the increased mass is the oxygen quality required for burning magnesium.

Paper is a mixture, the combustion is mainly the combustion of carbon, the result of combustion is the formation of carbon dioxide, the rest is those impurities, obviously, carbon dioxide is integrated into the air, the conservation of mass is known, and the mass is reduced.

If you know the chemical equation for the decomposition of potassium permanganate, you will know why the residue is less mass than the reactant, and the decomposition produces oxygen, water and potassium manganate. The rest you see is potassium manganate, and oxygen and buckets.

3. After the substance is heated in a vacuum and reacts, the total mass of the product must be equal to the total mass of the reactant.

After the fine iron wire is burned in oxygen, the mass of the product is greater than that of the fine iron wire, so this reaction does not obey the law of conservation of mass.

Obviously not, the iron oxide and ferric tetroxide generated, I don't want to talk about it below.

Brother, study hard, I've been in college for more than three years, and I think it's better to study in high school.

Since the products are formed by other gases, they volatilize, resulting in the conservation of mass, but it cannot be said that they do not obey the law of conservation of mass.

1.No, candles burn to produce carbon dioxide.

But carbon dioxide is not counted in the sum of the masses of the product, so that doesn't mean that the law of conservation of mass is not universal.

2.Paper is burned in the air and turns into ashes, and the mass of the ashes is smaller than that of paper.

3.The iron wire combines with oxygen in the air to form ferric tetroxide, so it is larger than the original iron wire.

1 Conservation of mass means that the mass of the substance remains unchanged before and after the reaction in the whole system, the candle burns and reacts with oxygen to form other substances, volatilizes into the air, and after the reaction, it is only called the candle, so the mass decreases, but does not conflict with the law of conservation of mass.

2 Magnesium strips are burned to produce magnesium oxide.

Paper burns to produce CO2

Decomposes to produce oxygen.

3 React in a closed system.

Set to generate x grams of potassium chloride.

2kclo3=△=2kcl+3o2↑

245 149x

245/ x=

The mass fraction of the solute in the saturated solution of the product at t°C.

2kclo3 =△，mno2= 2kcl + 3o2↑245 149

m245/ = 149/m

Get m = so solution mass = + 1*25 =

Mass fraction of solute in saturation = * 100% = 23%.

1) The mass of oxygen generated after the reaction.

The mass of oxygen produced by the reaction is grams.

2) What is the residue inside the tube? How many grams is the mass of each?

Let it be that x grams of potassium chlorate are required to generate gram O2, and at the same time, Y grams of potassium chloride are generated 2kClO3=2kCl+3O2

x－－－y－－

x grams, y grams.

2) What is the residue inside the tube? How many grams is the mass of each?

The residues in the tube were potassium chlorate, potassium chloride and manganese dioxide with masses of grams, grams and 3 grams, respectively.

Solution: Let the mass of KCl in the product be x.

2kClO3 (upper δ, lower mNO2) 2kCl+3O2 245 149

x245 x = water = 25g

Mass fraction of solute saturated in the product at t°C =

A: --

(1) The quality of oxygen produced.

2) Let the solute mass fraction of hydrogen peroxide be x

2h2o2=mno2=2h2o+o2

x68/x=32/

x=(3) If 100g of 3% hydrogen peroxide is prepared, how many grams of this hydrogen peroxide are needed?

y* y=4) The mass of hydrogen peroxide that has been decomposed in this bottle of hydrogen peroxide.

1000g*30%-z)/(1000g-32z/68)*100%=z=

(1) The quality of oxygen produced.

2) The solute mass fraction of hydrogen peroxide.

2h2o2=mno2=2h2o+o2

x68/x=32/

x=(3) If 100g of 3% hydrogen peroxide is prepared, how many grams of this hydrogen peroxide are needed?

y* y=4) The mass of hydrogen peroxide that has been decomposed in this bottle of hydrogen peroxide.

1000g*30%-z)/(1000g-32z/68)*100%=z=

First of all, it is generally known that manganese dioxide only plays a catalytic role: 1) It can be seen from the difference method that oxygen is generated because only oxygen escapes; 2) Write the chemical reaction equation by the mass of oxygen generated, so hydrogen peroxide is required, and the mass of hydrogen peroxide is required so w = 3) Let x g be required, then 3%*100=x*The solution is x= 4) If m g has been decomposed, then the mass of oxygen released is 32 (2*34) m g, so the equation (1000*30%-m) (1000-mo2) = solution is m=

(1) Solution: the mass of oxygen produced (3) y* y = (2) the solute mass fraction of hydrogen peroxide (4) the mass of hydrogen peroxide that has been decomposed in this bottle of hydrogen peroxide.

2h2o2=mno2=2h2o+o2 (1000g*30%-z)/(1000g-32z/68)*100%=

68 32 z=

x68/x=32/x=

Sulfuric acid mass 100*

According to the law of conservation of mass: the mass of hydrogen does not change before and after the reaction and is converted into hydrogen.

Hydrogen mass 2H2SO4*

According to the law of conservation of mass:

Total mass before the reaction Solid mass after the reaction:

The unit is grams).

Amount of sulfuric acid =

1 mol of sulfuric acid corresponds to 1 mol of hydrogen.

So the mass of hydrogen =

Mass of sulfate =

The mass of the solid is the mass of the sulfate + the mass of the metal mixture =

Is that 100% 100g?If so, keep reading below, if not, just ignore mine.

According to the relationship between one part sulfuric acid and one part hydrogen, the relationship is H2SO4 H2

In this way, the hydrogen gas that runs away is so that the solution is heavy, and the weight of the solid remaining after evaporating the water is.

According to the law of conservation of mass, the mass of the elements does not change before and after the reaction:

Magnesium, aluminum, zinc and iron are reacted with sulfuric acid to form the corresponding sulfate (mgSO4, Al2(SO4)3, ZnSO4, FeSO4), according to the law of conservation of mass, the mass of magnesium, aluminum, zinc and iron before and after the reaction is unchanged 5g:

Then just ask for the addition of the masses of (SO4) participating in the reaction:

Subtract H2 (the mass of hydrogen in the sulfuric acid participating in the reaction) from the mass of H2SO4 participating in the reaction

100g x

So, the solid mass: 5g+

Sulfuric acid quality. 100*

Amount of sulfuric acid =

1 mol of sulfuric acid corresponds to 1 mol of hydrogen.

So the mass of hydrogen =

Mass of sulfate =

The mass of the solid is the mass of the sulfate + the mass of the metal mixture = this is the most direct.

100g, the mass fraction of hydrogen in dilute sulfuric acid is 2 98 Hydrogen mass:

It is enough to calculate only the mass of the solid: hydrogen) + 5g =

According to the law of conservation of mass, as well as the order of metal activity, knowing that the final reaction of dilute sulfuric acid and magnesium is complete, it can be obtained: (1 2) h2*98*100*, the following question will not be, you can solve it yourself.

The mass of hydrogen comes from the hydrogen element in sulfuric acid, m(h2)=2 98*m(h2so4)=2 98*100*

Solution: Because of 5 100g of sodium hydroxide solution

So solute sodium hydroxide is 100x5% = 5g

Therefore, the mass of the sodium hydroxide solution after electrolysis is 5 10% = 50g, so 100g-50g = 50g of water is electrolyzed.

Suppose xg of hydrogen is generated.

Electrolysis 2H2O ====2H2 +O2

2x18 2x2

36g =4g

50g x50gx4g

x=———=

36g A: 50 grams of water were electrolyzed to produce grams of hydrogen.

Electrolyzed 50 g of water

Hydrogen is generated. Process: sodium hydroxide 100*5%=5g, electrolyzed solution mass 5 10%=50g

The water that is missing is 100-50 = 50 g

Hydrogen mass: 50*2 18=

(1) 2H2O2====2H2O+O2 (Manganese dioxide is a catalyst and does not participate in the reaction. ）

100 321000g×30％ x

x=962) isn't it 30%?

3) (4) I won't.

Let the electrolyzed solution be x g (100g 5%) x = 10% and the solution will give x = 50g, so the electrolyzed water is 100 50=50g and the hydrogen can be obtained according to the chemical equation 2h2o 2h2+o2.

(1) Greenhouse effect.

3) Replacement.

3CO+Fe2O3==2Fe+3CO2 (condition is high temperature).

(1) Greenhouse effect.

3) Displacement reaction.

Fe2O3+3CO== (High Temperature)2Fe 3CO2

(1) Silicon-based solar photovoltaic cells do not produce CO2 during use, which helps to solve the environmental problem of the greenhouse effect.

2) In nature, silicon mainly exists in the form of silicon dioxide (SiO2) and silicate. The valency of silicon in SiO2 is +4.

3) Industrially, carbon and silica are reacted at high temperature to produce silicon, and CO is generated at the same time.

The above reactions belong to the displacement reactions (fill in the basic reaction type).

Carbon monoxide can be used in industrial iron smelting. Write out the chemical equation for making iron from hematite as Fe2O3 + 3Co = High temperature = 2Fe + 3CO2.

(1).Greenhouse effect.

3) Replacement. 4) 3CO+Fe2O3 high temperature = 2Fe+3CO2

1.Greenhouse effect.

3.Redox reactions (displacement reactions).

4.Fe2O3 +3Co = 2Fe + 3CO2 (Condition High Temperature of the Reaction).

Greenhouse effect.

4. Redox.

Fe2O3+3CO== (High Temperature)2Fe 3CO2

1.Greenhouse effect.

2.+4 price.

High temperature = 2CO + Si

It is clearly a displacement reaction.

3CO+FE2O3=High temperature=2FE+3CO2

b...Here's why:

Because the liquefied air vaporizes, it absorbs a large amount of heat from the surrounding air, and the temperature of the wood strip drops below the burning point and then goes out.

Even if it does not reach the ignition point below the wood stick, the boiling point of nitrogen is lower than that of oxygen, and it will first vaporize into a liquid, while nitrogen does not support combustion, so it is extinguished.

Because the liquefied air vaporizes, it absorbs a lot of heat from the surrounding air, and the temperature of the wood bar drops below the burning point and then goes out.

c..The air mainly contains oxygen and carbon dioxide.

When turning on the liquidated air. Oxygen, which is less dense than carbon dioxide, is vaporized and discharged first. At this time, the wooden strips burn more vigorously. Then all the carbon dioxide is discharged, and the sticks are extinguished.

CO+CuO=Cu+CO2 mass increases.

28 44 44-28=16x 28g-20g=8gx=14g

The mass of CO2 in the original gas mixture is 20g-14g=6g

Carbon monoxide reacts with copper oxide, according to the chemical equation, every 28 grams of carbon monoxide reacts to gain 16 grams, and now the weight is increased by 8 grams, then the original carbon monoxide has 14 grams and carbon dioxide is 6 grams.