Junior 3 Chemistry Answer Questions Please give the reason completely Thank you

Question 1: 1) It must contain Na.

According to the law of conservation of mass, the types of elements that make up a substance before and after a chemical reaction do not change; In the first reaction, there are Na, C, and O elements in the product, and another reactant Co2 other than this particle can only provide C and O elements, so the particle must contain Na elements. In the second reaction, there are elements Na, Cl, O, and H in the product, and dilute hydrochloric acid (an aqueous solution of HCl, don't forget about water!). ) contains cl, o, and h elements, so the same conclusion can be drawn.

2) Drainage method.

According to the observable formation of gas, the gas is at least insoluble in water and can therefore be collected by drainage.

3）o2/co2

There's not much to say... There are only a few colorless and odorless gases that have been learned, and those that do not violate the known conditions can = =

4) Test O2: Stretch a small wooden strip with sparks into a test tube filled with the gas, if the wooden strip rekindles, it means that it is O2; If it does not rekindle, it is not O2;

Test CO2: The gas is passed into the clarified lime water, if it becomes turbid, it is CO2, and if it does not become turbid, it is not.

Question 2: 1) C+O2=ignition=CO2; c + CO2 = high temperature = 2CO

It's best to write these two steps separately, pay attention to the conditions.

2) 3CO + Fe2O3 = high temperature = 2Fe + 3CO2

There is nothing to explain, pay attention to the reduction of iron ore is CO gas and not coke (C), pay attention to the conditions.

5000×84%=4200（t）

Let pig iron x t, which contains 98% iron, be smelted, then the iron element is conserved:

4200×（2×56/160）=98% x

Solution x=3000

Therefore, 3000t of pig iron can be smelted

1) Na O reacts to form Na and new hydrochloric acid to form H2O (but I don't know what it means to be able to see the formation of water in the experimental phenomenon).

2) Drainage method.

3) O24) with a strip of wood with Mars stretched into the gas, Mars rekindled Conclusion: Oxygen.

Five: (1) 2C + O2 = high temperature = 2CO

2) Fe2O3 + 3Co = high temperature = 2Fe + 3CO23) A 56 * 2 + 16 * 3 = 160

b 5000t*84%=4200t

c 4200t*（56*2/160）/98%=3000t

Four (1)Na It reacts with CO2 and only produces Na2CO3 and O2, and when it reacts with dilute hydrochloric acid, it only produces NaCl, H2O and O2,2) drainage method.

3) O24) collects part of the gas in the test tube, approaches it with a wooden strip with sparks, and the wooden strip rekindles, then the gas is O2

Five (1) 2C+O2=2Co C+O2=CO2 CO2+C=2CO2)Fe2O3+3Co=2Fe+3CO2

3)①56x2+16x3=160

5000tx84％=4200t

fe2o3+3co=2fe+3co2

4200t xt

The solution is x=2940t

The above-mentioned hematite can theoretically be smelted to obtain pig iron containing iron 98, which is 2940 98% = 3000t

1) When Na reacts with CO2, Na2CO3 and O2 are generated, and according to the total class of elements before and after the chemical reaction, the extra Na comes from it!

2) Drainage method or upward exhaust air method (3) O2

4) Step: Collect a test tube of the gas and place it at the mouth of the test tube with a wooden strip with sparks. Phenomenon: Re-ignition of the wooden strip with Mars was discovered, conclusion: O2 was proven

Five. 3. 160 42000t 3000t

This is not the knowledge of the third year of junior high school, the knowledge of the first year of high school, this substance is Na2O2 (sodium peroxide). Contains sodium and oxygen, because it reacts with hydrochloric acid to produce sodium chloride, water and oxygen: according to the type of elements before and after the reaction, hydrogen and chlorine are known before the reaction, and there are sodium, chlorine, hydrogen, and oxygen after the reaction, so there must be sodium and oxygen before the reaction.

With the drainage method, or by using the upward exhaust method, the gas produced is oxygen. The gas produced is, oxygen. Proving that the gas produced is oxygen, textbooks have it.

a cl b o c h d mg

I didn't tell you why, I'll tell you. First of all, if you can reflect with the letter, there must be hydrogen ions to produce hydrogen! And if it is a Ca compound, then C is H.

But what element does h have a one-to-one ratio? The first thing that comes to mind is that a is chlorine, and the second thing that comes to mind is fluorine. Knowing that the number of electrons outside the nucleus of atom A and atom D is the same, and knowing that the total number of electrons outside the nucleus of atom B and atom D is equal to 4 times the number of electron layers of each of them, these two elements can form a compound of DB type, assuming that B is oxygen, then 2*4+3*4=20, and then 20-8=12, and then reverses d to mg, which is in line with the topic, and then returns to the condition that "the number of electron layers outside the nucleus of atom A and atom D is the same", and we know that A is chlorine.

Among them are the gases that form HCl, Cl2, Cl2O7, and so on.

Ca is an acid from "knowing that the solution of Ca can react with zinc to produce hydrogen", Ca is an acid, a substance learned in junior high school can be judged to be HCL, and from "the number of electron layers outside the nucleus of atom A and atom D is the same," we can know that C is H, A is Cl, and the electronic configuration of chlorine is

Then the number of electrons outside the nucleus of element d is 3, the total number of electrons is 12, and d is magnesium, and because the number of nuclear charges is between 1 and 20, the total number of electrons outside the nucleus is equal to 4 times the number of their respective electron shells, respectively, only oxygen and magnesium, then b is oxygen.

Then (1) the names of elements a, b, c, and d are chlorine, oxygen, hydrogen, and magnesium, respectively (is the atomic structure diagram omitted?). ）

2）hcl、（o2、cl2）

a:cl b:o c:h d: mg You can try to see it yourself to help with memory.

2）hcl (cl2o7 clo3..)

There is no picture, and we can't help you until dawn, wash and sleep, and tomorrow I will ask the teacher to tell us that we have produced precipitation, which is a message.

na2co3---baco3

106 197x x= It is known that there is Na2CO3, that is, there is it in the sample.

Then the NaOH mass fraction.

12 o 16.In CO2, C:O is already 12:32=3:8 plus oxygen. It's going to be less than 3:8, so it's not going to be 3:5

The valency of medium carbon element +2 becomes CO2 after the reaction of carbon element valency +4The elevated valency is reduced as an oxidizing agent.

3.The mass that runs away is the gas CO2, which is CO2Write the equation to know that the copper oxide is reduced, and the mass of copper oxide is 16g.

Pyrolysis ==Cao + CO2

CaCO3 + 2HCl === CaCl2 + H2O + CO2 are all one-to-one to produce CO2 so there are as much.

5.Air convection relies on heavy air to run down, light air to go up, weightlessness The carbon dioxide produced by combustion cannot sink, oxygen cannot be replenished, and it will naturally be extinguished without oxygen.

It is a reducing agent, and the reducing agent undergoes a reduction reaction.

caco3=cao=co2

CaCO3:CO2 is 1:1

5.The air is convection, and without oxygen, the flame is immediately extinguished.

1 Alcohol does not dissolve rust a, no; When a substance is dissolved in water, there will be a heat of melting, which is generally accompanied by temperature changes, b pairs; There are blood proteins in the bloodstains, and the enzymes in the enzyme laundry detergent can digest the proteins, and it is said that they can remove the bloodstains, C is right; Concentrated hydrochloric acid will volatilize, and when it encounters water vapor in the air, it will combine to form small droplets of hydrochloric acid, so there will be white mist, d is also right... Yes, there is BCD.

2 xy is juxtaposed and both are contained in z, which should be c There are no oxides in the acid-base salt, and the two are juxtaposed, but both are compounds.

3 A in S burns in O2 and only SO3 is generated. In B, the excess of CO2 into lime is the formation of calcium bicarbonate, and a small amount is the formation of calcium carbonate, which is related to the amount of CO2.

c Charcoal is fully burned in oxygen to generate CO2, and if the combustion is not sufficient, there will be CO generation, which is related to oxygen content.

The products in d are more complicated, what monohydroamine phosphate, ammonium dihydro, and ammonium hydrogen phosphate are related to the amount of ammonia, so choose a

1.The following statement is correct (

a.Alcohol washes away rust from tiles.

b.When a substance is dissolved in water, it often changes the temperature of the solution.

c.The enzymes in enzyme-fortified laundry detergents help to wash away blood stains from clothes.

d.Concentrated hydrochloric acid is placed in the open, and white smoke rises in the air.

a, because the covalent bonds in the alcohol, i.e., ethanol, do not react with iron ions, the alcohol does not wipe off the rust. The claim is false.

b This statement is true, because chemical reactions are accompanied by endothermic and exothermic processes. But only part of the reaction is an exothermic process, so the statement of temperature change is incorrect.

C is correct, because the alkali in the laundry detergent can undergo saponification reaction, it can be used to wash other soluble ions in the laundry, but the blood stains are organic matter that can decompose proteins and other substances, and it is easier to saponify the reaction, so the statement is correct.

D is wrong, white smoke can only be seen under certain humidity conditions, such as a breath.

2.Figure 1 can show the juxtaposition of m and n, and Figure 2 can show the subordination of m to n. The relationship between the following concepts is consistent with the relationship shown in Figure 3 ().

x y za.Solut solvent solution.

b.Suspension emulsion solution.

c.Oxide acids, bases, salt compounds.

d.Saturated solution Unsaturated solution Concentrated solution.

Only option b is correct.

A solute is insoluble in solvent incorrect, c acid base salt is overall so incorrect, d unsaturated solution concentration can be very low but not concentrated solution so wrong.

3.When the relative dosage of the reactants is adjusted, the following reaction products do not change ( ).

a.Sulfur is burned in oxygen.

b.Carbon dioxide is passed into the lime water.

c.Charcoal burns in oxygen.

d.Ammonia gas is introduced into the phosphoric acid solution.

a, the statement is wrong, there is sulfur dioxide and sulfur trioxide will change. b statement is correct, there is only one product, calcium carbonate. c. Charcoal combustion will produce carbon monoxide and carbon dioxide, so the statement is wrong, d ammonia can produce two things: mono phosphate and ammonium phosphate.

I remember that there should be no multiple-choice questions in the third year of junior high school... The best option for the words.

1、c2、b

3. A should be right.

1:bc

2: AC3:A Question 1: When a substance is dissolved in water, there will be a heat of melting, which is generally accompanied by a temperature change, B pair; Blood has blood protein, and the enzyme in the enzyme laundry detergent can digest the protein, saying that it can remove blood stains, C right.

Question 2: There must be solvents and solutes in the solution, a right; The compound contains oxides and acid-base salts, C pairs.

Question 3: All are generated to produce sulfur dioxide, nothing else, a right; If carbon dioxide is introduced into lime water, it will produce precipitation, but calcium carbonate precipitation will be combined with water and carbon dioxide to produce soluble calcium bicarbonate, b wrong; Carbon is burned in oxygen to produce heat, and carbon reacts with oxygen to produce carbon dioxide, but carbon dioxide reacts with excess carbon at high temperatures to produce carbon monoxide, c wrong; The products in d are more complex Ammonium dihydrogen phosphate Diammonium hydrogen phosphate and ammonium biphosphate, etc., which are related to the concentration of ammonia.

1, a rust is not clear b temperature is generally unchanged c is very right d is white fog, white smoke is tiny particulate matter choose c2, choose a, there is no reason, go to the book to find the concept to go 3, a sulfur if burned in sufficient oxygen to produce sulfur dioxide, insufficient sulfur monoxide, b no problem c sufficient oxygen to generate carbon dioxide, insufficient carbon monoxide d is very complicated, you don't need to understand、、、 give a little points, i chemistry full score i have done these questions i don't know how many times... Absolutely, trust me.

1C rust is Fe2O3 and insoluble in ethanol. HCL emits white mist. Many things dissolve in water and do not change.

2c Without much explanation, go back and look at compulsory one. Classification of substances.

3a is all sulfur dioxide calcium bicarbonate in excess, the appropriate amount is calcium carbonate carbon monoxide when there is less oxygen is mostly carbon dioxide d very little ammonium dihydrogen phosphate, then ammonium monohydrogen phosphate, then ammonium phosphate.

BAA has the heat of dissolution here2 to understand for yourself, 3 only produces sulfur dioxide. The others have two products, and D has three products.

A: Aluminum is the earliest metal material used by human beings is copper.

B: Copper is currently the metal with the highest annual production in the world. --Is iron c: Most metallic elements exist in nature in elemental form. --Mostly in the form of compounds.

A: The first metal to be used was iron.

B: The metal with the highest annual production in the world is iron.

c: Most metal elements exist in the form of compounds in nature D: (1) The melting point of most alloys is lower than the melting point of any of the constituent metals in their components;

2) The hardness is greater than the hardness of any metal in its components;

3) The electrical and thermal conductivity of the alloy is lower than that of any group of metals. (4) Some have strong corrosion resistance.