Chemistry questions in junior high school are in the supplement Kneel and beg

1]3 sodium carbonate.

The preparation method is the third step of the equation.

1) NH3+H2O+CO2=NH4HCO32)NH4HCO3+NACl=NH4Cl+NaHCO3 3)2NaHCO3 (heating)=NA2CO3+H2O+CO2 2] 2 Copper sulfate.

It can be seen from the ** that it is blue, which is the color of copper sulfate pentahydrate.

3] 1 hydrated lime.

This is the main use of calcium hydroxide, which is introduced under the ninth grade of chemistry in the people's education version.

4] 5 NaCl.

Table salt is commonly known as sodium chloride, and salt (such as cured meat) is commonly used before the use of preservatives5]4 sodium nitrate.

It contains both nitrogen and potassium, so it is a compound fertilizer.

Sodium carbonate: commonly known as soda ash.

Copper sulfate: divalent copper sterilization.

Hydrated lime: weak alkali.

Sodium chloride: table salt.

Potassium nitrate: nitrogen and potash.

1) The soda ash prepared by the "Hou alkali making method" is - 3 sodium carbonate.

2) What can be used for swimming pool disinfection is - 2 copper sulfate.

3) Commonly used in agriculture to improve acidic soils is - 1 hydrated lime.

4) The commonly used condiment, which can also be used for food preservative, is 5 sodium chloride.

5) The compound fertilizer used in agriculture is - 5 potassium nitrate.

3 Although the aqueous solution is alkaline, the guy is salt.

2 Bivalent copper can be used for disinfection.

1. Alkali should be used to cover the acidic soil of the face, and the alkali is hydrated lime, that is, calcium hydroxide, is the cheapest.

5 The composition of salt is sodium chloride.

4. Compound fertilizer potassium nitrate contains two kinds of kn.

1) The soda ash prepared by the "Hou alkali making method" is - 3 sodium carbonate.

2) What can be used for swimming pool disinfection is - 1. Hydrated lime.

3) Commonly used in agriculture to improve acidic soils is - 1 hydrated lime.

4) The commonly used condiment, which can also be used for food preservative, is 5 sodium chloride.

5) The compound fertilizers used in agriculture are- 4. Potassium nitrate.

1.Sodium carbonate.

2.Copper sulphate.

3 hydrated lime. 4.Sodium chloride.

5.Potassium nitrate.

2) The best answer is 1, but if you can't repeat the choice, 2 is also correct.

1:3 is commonly known as soda ash.

2:2 bivalent copper sterilization.

3:1 weak base.

4:5 table salt.

5:4 nitrogen and potassium compound fertilizer.

1) The soda ash prepared by the "Hou alkali production method" is sodium carbonate |Na2CO32) can be used for swimming pool disinfection is - copper sulfate CUSO43) commonly used in agriculture to improve acidic soil is - hydrated lime CA(OH)24) commonly used condiments, can also be used for food preservative is - sodium chloride NaCl5) belongs to the compound fertilizer used in agriculture - potassium nitrate KNO3

So many experts got it right.

Wrong, don't blame me--

1.Lithium (Li) and Oxygen (O) Li2O lithium oxide.

2.(1) The combustion of white phosphorus will produce a large amount of white smoke, and the smoke is solid and small particles, so the first empty I think is phosphorus pentoxide solid, and the second empty should be air.

2) Large Because it is open, it is equivalent to a leakage of the device, and the product of white phosphorus combustion is phosphorus pentoxide (solid), so the mass increases.

1. The element with atomic number 3 is lithium, and element 8 is oxygen, so the chemical formula of the compound is Li2O (2 is the subscript).

2. Tighten the cork immediately after the ignition of red phosphorus, the reason is that if the cork is not tightened immediately, the phosphorus pentoxide, the combustion product of red phosphorus, runs out of the gas collection cylinder, which makes the balance unbalanced during the experimental measurement, and the result is small.

If the combustion is cooled and placed openly: because the red phosphorus burns a large amount of white smoke is the product of phosphorus pentoxide, after cooling the open place, the outside air will enter the bottle, making the measurement result larger.

2.Phosphorus pentoxide is the air that goes in.

In the end, the result of weighing is smaller than the original, because the scale pentoxide scale, which is burned by the scale, is spread into the air by the open mouth, so that the gas collected is reduced, and it is judged according to the conservation of mass. In reactions with the participation or generation of gases, errors should be prevented in a closed container.

（1）li2o

2) P2O5, air.

Because if the cap is opened, the P2O5 particles will escape, resulting in a decrease in the quality of the front and back; When the lid is opened after the combustion has cooled, the air pressure inside the bottle is lower than the atmospheric pressure, so the air will rush in, causing the mass to rise.

k：i：o=39：127：48

Mass fraction of i=127 (39+127+48)mass of NaOH 125*10%=

The second part of the measurement of water is that is.

Part 3 Add NaOH and stir to dissolve.

Is hydrochloric acid by lz hydrochloric acid mass fraction? I'll just do that.

hcl + naoh=nacl+h2o

50* xx=40*50*

The mass fraction of NaOH in the remaining solution is 4 (125-5)*100%=

The ratio of iodine to oxygen to mass is: 127:16*3=127:

The mass fraction of 48 iodine element is 127 (39+127+16*3)=25The mass of NaOH is: 125*10%= 2

Weighing. 3。Dissolve.

naoh + hcl ==nacl + h2ox=4g 50*

Mass fraction of NaOH in the remaining solution: 4 (125-5)=

25 (1)12,5, 2 Weigh NaOH 12,5g with a balance,3 Pour 12,5g of NaOH solid into water to dissolve.

2）naoh ＋ hcl = nacl ＋ h2om（naoh） 50g×

m（naoh）=4g

naoh）=4g/120g ×100％=

ca(oh)2+na2co3==caco3↓+2naoh106 100

x 5g106/x=100/5g

x=Mass fraction of sodium hydroxide in sodium hydroxide solids (

1. When checking the air tightness of this device, the right gas outlet nozzle should add a latex tube, clamp it with a spring clip, and then add water in the long neck funnel, if a liquid seal is formed, the liquid level in the funnel will no longer fall, and the air tightness is good. Because the right catheter orifice is sealed, the liquid level will not drop if there is no air leakage.

2. The long-neck funnel cannot be inserted under the liquid, and it will leak when gas is generated (gas escapes from the lower end of the funnel). After placing a small test tube, it is still required that the liquid level in the small test tube should be high enough to form a liquid seal under the liquid level of the long neck funnel inserted into the small test tube, so that there will be no air leakage.

3. Note that the drying tube should be filled with lumpy insoluble solids, and the liquid level in the beaker should be higher than the thin tube under the drying tube. When it is necessary to collect the gas, the spring clamp is opened and the liquid in the beaker reacts with the lumpy solid in the drying tube. When the spring clamp is clamped, the gas cannot escape from the right end of the conduit, so that the liquid in the dryer tube is pressed out of the dryer tube, so that the solid is separated from the liquid and the reaction is stopped.

It can be made and stopped.

4. The principle is similar to 3, which requires that the lower end of the long-neck funnel should be lower than the empty plastic plate, and the liquid level should be higher than the empty plastic plate. When it is necessary to collect the gas, the spring clamp is opened, and the liquid in the funnel reacts in contact with the bulk solid on the plastic plate. When the spring clamp is clamped, the gas presses the liquid in the tube back into the funnel, causing the solids to detach from the liquid and stop the reaction.

It can be made and stopped.

5. The principle is the same as 3, which requires the rupture of the bulk solid in the test tube. In addition, it can also be understood that when gas is required, the test tube can be reacted by putting it in the liquid, and when the gas is not generated, the test tube will not be reacted when it is removed.

6. Put the glass filament on the right side of the U-shaped tube, and put the lumpy insoluble solid on the glass filament, which is similar to the principle of 3. When no gas is needed, the right side closes the spring clamp and the resulting gas stops the reaction by pressing the liquid back to the left side.

7. This is a typical Qipu generator. There are two hemispherical funnels outside, and there is a gap between the lower end of the spherical funnel and the hemispherical funnel, which allows the liquid to enter and exit, and the water-insoluble solid is added to the hemispherical funnel above, and the liquid is added from the long-necked funnel, and when the solid-liquid comes into contact, the reaction produces gas, and when the spring clamp is clamped, the gas is pressed back into the long-necked funnel. The principle is also similar to 3.

8. Carbon dioxide can be used as a fire extinguishing agent, first of all, carbon dioxide does not support combustion, and can isolate combustible substances from contact with air, and secondly, carbon dioxide is denser than air, and carbon dioxide will relatively sink on the surface of combustibles when extinguishing fires, enhancing the fire extinguishing effect.

9. Whether the carbon dioxide ball will float depends on the difference between the buoyancy and gravity of the balloon in the carbon dioxide atmosphere, if the buoyancy is greater than the gravity, it will float, otherwise it will not float. If the buoyancy force is equal to the gravitational force, it may levitate. This is a matter of physics, buoyancy is equal to the volume of the balloon multiplied by the density of carbon dioxide.

10. When electrolyzing water, dilute sulfuric acid should be added to enhance the conductivity of the solution. If dilute hydrochloric acid is added, hydrogen is obtained at the cathode and chlorine is obtained at the anode. Oxygen is not available.

Hope it helps.

1.It is the principle of physics, the atmospheric pressure inside and outside the funnel is equal, so it leads to the formation of a liquid seal in the funnel2Be anti-gasp.

3.If you want the reaction to stop, just take out the device in the beaker and the reaction will stop immediately4The reaction produces gas, and when sealed, the reaction is squeezed into the funnel, causing the reaction to be lower than the perforated plate, so that the reaction stops without reacting with the lumpy object on the porous plastic plate.

5.Same as the 4 principle.

6.Prevent the liquid from suddenly flowing back into the funnel, causing the funnel to disengage from the device 7Same as the 4 principle.

One is heavier than air, and the other can block the contact between the burning material and the air, and cut off one of the three elements of combustion.

It doesn't float, it just stays at the bottom of the cup.

10.Dilute sulfuric acid increases electrical conductivity and cannot make dilute hydrochloric acid.

The main root is airtight, the pressure is the same, and it is too troublesome to type, and it is very convenient to say it directly.

Why can CO2 be used as a fire extinguishing agent because it is denser than air?

CO2 does not support combustion!

9.The beaker has two balls, one is an air ball and the other is a ball containing CO2, and carbon dioxide is poured all the way into it. The air balloon will float, so will the carbon dioxide ball float? Levitation?

The ball of CO2 is suspended.

10.When electrolyzing water、Why to increase electrical conductivity,。 Is dilute sulphuric acid or dilute hydrochloric acid added? Dilute sulfuric acid.

According to the question, 20kg of children should be taken from oral solution daily (

Known branches. So 1 stick is needed.