Junior 3 Chemistry can be selected more than 20

The answer is a and c, since copper oxide can only react with acid, so E is copper oxide, B is dilute sulfuric acid, propylene must be copper sulfate, A and D may be iron, or sodium hydroxide, the two can be interchangeable positions, so b and d are correct.

A physical reaction of gravity.

b molecules irregularly move and temperature, the higher the temperature, the more intense the thermal movement and the body reacts.

c. Chemical reactions.

dMolecular diffusion physical reactions. Choose.

B can react with three substances, it must be dilute sulfuric acid, so propylene is copper sulfate, E is cuo, and methyl butyl is uncertain. So A is wrong, C is wrong, choose AC

Haven't you already done it.

a、b、c

Level 16 says there is iron oxide. Is there a title? ac

1 Correct (the most basic, water in nature contains minerals) 2 False (the eutrophication pollution of the water body is caused by P) 3 Correct (heating and boiling promote the precipitation of calcium ions and magnesium ions in the water, and the hardness is reduced) 4 Correct (Water is a good solvent, and the inter-ion reaction in the aqueous solution is sufficient).

2 Definitely false The eutrophication pollution of water bodies is that the water contains too much nutrients such as nitrogen, phosphorus, potassium and so on.

Just remember it correctly, no need to explain, it's common sense.

2. Eutrophication pollution of water body refers to the excessive presence of nutrients such as nitrogen, phosphorus and potassium in water, and the increase of calcium ions and magnesium ions will cause water quality to harden.

The correct answer is: 2

1. Water is the most common solvent No problem, "water in nature contains a variety of minerals" A variety of minerals are impurity ions such as Ca ions, magnesium ions, Na ions, etc.

2. The main theory of water eutrophication is that too much nitrogen, phosphorus and sulfur causes eutrophication of water bodies, so 2 is wrong.

3. Hard water refers to the high content of Ca and iron ions in water, and boiling distillation can remove these elements in the form of precipitation (rust).

4. After the substance is dissolved in water, the chance of contact between the ions is increased, so the reaction speed is fast and sufficient.

The following knowledge about water, of which is incorrect is (2 4 )1Water is one of the most common solvents, and most of the water in nature contains impurity ions such as Na+Mg2+Ca2+

2.The increase of calcium ions and magnesium ions in water will cause eutrophication of water bodiesEutrophication of water bodies: mainly pollution of P-containing substances (such as phosphorus-containing detergents, pesticides, etc.) 3Boiling or distillation can reduce the hardness of the water.

For example, during boiling, the following reaction often occurs, which reduces the concentration of calcium ions Ca(HCO3)2=CaCO3+CO2+H2O4A chemical reaction occurs in an aqueous solution, and the reaction speed is relatively fast and sufficient, and there are some slow and some fast.

For example, the acid-base neutralization reaction, the reaction between metal sodium and water is very fast, and the rust of steel in water is relatively slow.

1 Correct (the most basic, water in nature contains impurity ions such as calcium, magnesium, sulfate) 2 False (the eutrophication pollution of water bodies is caused by the compound of P, so phosphorus-free laundry detergent is now introduced).

3. Correct (the content of calcium ions and magnesium ions in the water is the hardness index of water, heating and boiling can promote the precipitation of calcium ions and magnesium ions in the water, respectively, to form calcium carbonate and magnesium hydroxide, which are the main components of scale, and the calcium and magnesium ions in the water are reduced and the hardness is reduced).

4. Correct (the substance is dissolved in water to form a homogeneous medium, which is conducive to the reaction).

2 Calcium ions and magnesium ions are hardness, and only eutrophication pollution will be contained in N p

Stop using ammonium sulfate and switch to potassium sulfate Potassium sulfate did not improve acidic soils.

2.When fertilizing in the next year, mix ammonium sulfate and hydrated lime to produce ammonia and reduce fertilizer efficiency.

3.When fertilizing the next year, mix ammonium sulfate and quicklime with 24After the crops are harvested, they are sprinkled with grass ash in the field The grass ash is alkaline and can improve the acidic soil.

The answer is that ammonium sulfate hydrolysis is acidic, and potassium sulfate is not hydrolyzed, so 1 pair of soil is neither improved nor deteriorated; 2. The two substances, one acidic and the other alkaline, react with each other, which is equivalent to adding nothing, and has no fertilizer effect at all, 3 and 2 are the same; 4. Potassium carbonate, the active ingredient of plant ash, is alkaline in hydrolysis, which can counteract the effect of ammonium sulfate and restore the soil to normal pH value.

1. That's right. Charcoal glows white when burned in oxygen, and only turns red when burned in air.

2. Yes, the white solid generated is magnesium oxide.

3. It is also true that igniting carbon monoxide is a blue flame, and the product is carbon dioxide, which makes the clarified lime water turbid.

4. No, copper oxide is insoluble in sodium hydroxide solution, so there is no precipitation.

4. Because copper oxide cannot be soluble in sodium hydroxide, it will not react with sodium hydroxide to form precipitate.

d.Copper oxide does not react with sodium hydroxide.

4 Wrong, copper oxide does not react with sodium hydroxide.

1 pair, charcoal burns red in the air, and burns white light in oxygen.

2 pairs, the reaction of magnesium strip combustion is very violent, emitting white light, generating magnesium oxide.

3 pairs, carbon monoxide burns a blue flame to produce carbon dioxide, and carbon dioxide reacts with calcium hydroxide in lime water to produce barium carbonate precipitate.

4 False, copper oxide will not be unable to react with sodium hydroxide solution and will not produce precipitation.

d is not right, the alkali is not reflected with metal oxides, so it is not right.

The answer is 4 metal oxides can only react with acids and not with bases.

1.Yes, charcoal glows more vigorously when it is fully burned in oxygen, and it only turns red when it is burned in the air.

2.Yes, magnesium burns in the air, producing a dazzling bright light that produces a white solid MGO3Yes, carbon monoxide produces a blue flame when burned, and the carbon dioxide produced can be lime water into calcium carbonate precipitation.

4.No, metal oxides can only react with acids, not with bases.

、It's all very basic,4 This sentence doesn't have this general technique.,There can't be this type of junior high school.,Remember that it's soluble without acid.。

2. It is the phenomenon of combustion in oxygen.

1. Carbon is fully burned in oxygen, so it is more vigorous than air. Right.

2. Magnesium is burned in the air to produce white magnesium oxide. Right.

3. When carbon monoxide is burned, a blue flame is generated, and carbon dioxide can be converted into lime water into calcium carbonate precipitation.

4. Can't react wrong.

The answer is that DA combustion is mainly a reaction with oxygen, so the concentration of pure oxygen is higher than the concentration of oxygen in the air, so the combustion is more vigorous.

B magnesium burns in the air, producing a dazzling bright light and generating a white solid MGO;

Magnesium burns more violently in oxygen.

c flame is light blue, with a dry beaker cover above the flame without water beads, with clarified lime water wet beaker over the wall above the flame turbidity and oxygen ratio is easy to occur, the product is CO2

D does not react because Cuo is insoluble in water.

It is B, C that cannot be successful

a, according to the smell of combustion, the degree of combustion.

B, lime water and soda ash solution are alkaline, the atmosphere phthalein can not be identified C, table salt and industrial salt (nano2) are tasteless, both are white crystals, can not identify D, which mainly uses baking soda and acid to undergo a chemical reaction to generate CO2

Answer D, Reason:

The difference between table salt and industrial salt.

1.Structurally: table salt is a purer sodium chloride, and the chemical formula of sodium chloride is NaCl, which is composed of chloride ions and sodium ions.

In addition to sodium chloride, there is also sodium nitrite that exceeds the standard, and its chemical formula is nano2, and the formula is composed of nitrite ions and sodium ions.

2.Properties: The nature of salt is relatively stable, and the aqueous solution is neutral. Sodium nitrite is relatively stable under dry conditions, but it can slowly absorb oxygen and oxidize to sodium nitrate, and the aqueous solution is alkaline.

3.Appearance: Both are white, and in special cases, table salt may also appear yellow or light blue, and sodium nitrite may also appear slightly yellowish. Both are crystalline and have a certain difference in geometry under the microscope, but they are not distinguishable with the naked eye.

4.Solubility: Sodium nitrite and table salt are very soluble in water, easy to deliquescent, and odorless.

5.Taste: Sodium nitrite is slightly salty, and table salt has a strong salty taste, which is difficult to distinguish by taste when eating.

From the above comparison, it can be seen that sodium nitrite is similar to salt in appearance and taste, and is easy to cause accidental ingestion poisoning.

Choose B and C, both solutions B are alkaline, and phenolphthalein is red dropwise, and C, both are white crystals, which cannot be judged.

1. The chemical equation of alcohol combustion reaction C2H5OH+3O2=2CO2+3H2O The mass ratio of each substance is 46:96:88:

54 The result is 23:48:44:

27 Option A

2. The reaction gives It can be known that the mass ratio of phosphorus and oxygen to participate in the reaction is 124:160 and the approximate score is 31:40 According to the law of conservation of mass, the mass of the product is equal to the total mass of each reactant, so the product should be 71 The answer is d

1. C2H5OH+3O2=2CO2+3H2OAccording to the equation: there are 46:3*32:2*44:3*18, that is, 23:48:44:27

Select a p+5o2=2p2o5

According to the equation: the mass ratio of individual substances is equal to their coefficient multiplied by the ratio of their relative atomic weight, i.e. it is consistent with 4*31:5*32:2*142=31:40:71 and choose d

1, C2H5OH+3O2=2CO2+3H2046 : 96 :88 :54 and then reduced to the simplest ratio.

Choose 124 160 284

Simplest to choose D

D is also wrong, the mass ratio of z and w of the reaction is (16-6) :(16-11) = 10:5 = 2:1

Other questions can be asked

16 questions AC, 17 questions CD, 18 questions D. If necessary, please ask

1 Conjecture basis.

Air is inexpensive.

In the N2 nitrogen atmosphere, the food is not perishable easily and is inexpensive.

CO2 CO2 atmosphere, food is not easy to spoil, and the cost is low.

2 Operation: Pass the gas in the bag through the clarified lime water.

Phenomenon: If there is no significant change in the clarified lime water, it is N2, and if the clarified lime water becomes turbid, it may be air or carbon dioxide.

Hypothesis Nitrogen, on the grounds that it does not provide breath and is one of the components of air.

CO2, same reason as above.

Noble gases, for the same reason.

2. The gas in the packaging bag is passed into the clarified lime water, and if it becomes turbid, it is CO2.

A. At point A, the silver nitrate does not all participate in the reaction, and the solution contains silver nitrate, copper nitrate and zinc nitrate generated, and the solutes are three kinds, so A is wrong;

At point b and b, all the silver nitrate participates in the reaction, and the solid formed is silver, so b is wrong;

At point C and C, the copper nitrate happens to be completely reacted, and there is only zinc nitrate in the solution, so C is correct;

When there is an excess of zinc at point D and d, the solids obtained are silver, copper and zinc, so D is wrong;

Therefore, select C and note that point A is not on the coordinate axis.