A few chemistry questions in the homework junior high .

I'll add. 3. The state of carbon in the combustion of charcoal in O2 changes, and it has the original elemental state and becomes a compound after a chemical reaction.

The state is from the free state to the chemical state. The other elements of carbon are chemical compounds.

4. Take a small amount of sample and add it to water, take the upper layer and add phenolphthalein test solution dropwise at night to see if it turns red. Because if it is decomposed, calcium oxide should be generated, and after adding water, the supernatant is lime water, and the phenolphthalein test solution turns red.

1。selection of clarified lime water; Vinegar, because the main ingredient of shells is calcium carbonate, and the main ingredient of vinegar is acetic acid, the reaction of the two can produce carbon dioxide, and the carbon dioxide produced makes the clarified lime water turbid.

2。The first calcination can be done without a change in valency and no reducing agent is required.

The second addition of water has no change in valency and does not require a reducing agent.

The third one can be dissolved in water without a change in valency and does not require a reducing agent.

The fourth one requires a reducing agent, which reacts with C at high temperatures to form CoC, which takes away the oxygen from carbon dioxide, which is the reducing agent.

Question 1: The main component of shells should be calcium carbonate (CaCO3) There is a formula in chemistry CaCO3 + HCl = CAC2 + H2O + CO2....Vinegar contains HCl....

It is also necessary to check whether it is CO2 or not, so it is necessary to choose clarified lime water and vinegar.

Question 2: CaCO3==(High Temperature)CaO+CO2CaCO3+H2O==Ca(OH)2

co2+h2o==h2co3

CO2+C==(Heating)2CO The answer is: CO2-CO If there is anything you don't understand, **.

1.Bronze (Bronze Age) Iron (Spring and Autumn) Aluminum (Modern) 2Stoneware, pottery, bronze, iron, steel and concrete, light alloys and composites, silicon and polymer materials stage, titanium and titanium alloys .........In this case, you can't fill all the blanks, but there are so many of them, you can pick a few yourself.

3.Melting point, boiling point.

After the fight, I found out that I was preempted again.

1.Bronze (Bronze Age).

Iron (Spring and Autumn) Aluminum (Modern).

2 Stoneware Bronze Ware Iron Ware Plastic Ware Nano.

3. Melting point Melting point.

5.Many substances can react with water, and among the following substances, the one that cannot be prepared by direct reaction with water is (

A, H2SO4, SO3 is obtained when dissolved in water.

B, NaOH and Na2O are dissolved in water to obtain.

C, H2CO3, CO2 dissolved in water obtained.

d, fe(oh)3, this is not obtained.

Select D6The following equation cannot be achieved by one-step reaction: (A: Cuo Cu(OH)2 , Cuo is insoluble in water and takes many steps to obtain.

B: BaCl2 Ba(NO3)2, plus AGno3 to get it.

C: Cu(OH)2CuCl2, plus HCl to obtain.

D: Fe FeCl3, this can be obtained, Fe reacts with Cl2.

Choose A7The salts that can be prepared by direct reaction between metal and dilute hydrochloric acid are ( )A, CuCl2, and Cu does not react with HCl.

B. AGCL, AG does not react with HCL.

C. MgCl2, Mg reacts with HCl.

D, FeCl3, Fe and HCl can only obtain ferrous iron. Select C

1. The main elements in salt are sodium and chlorine, and due to the addition of iodine-containing potassium iodate kio3, there are also iodine and oxygen.

Table salt is crystals, and crystals have a regular shape structure. Hydrogen, chlorine, and sodium hydroxide are obtained by electrifying the salt water.

2. These things are related to chemistry. It seems to be related to human habitation and transportation.

This is an open-ended question, and everyone has their own opinion.

3. Color first, then state.

1: The shape of NaCl salt is formed by its structure The new substance obtained by the melting and electricity of table salt is sodium metal and chlorine The new substance obtained by the electricity of the salt solution is chlorine, oxygen, hydrogen and sodium hydroxide solution.

2 tablets, acrylic sweater, coal, vinegar, gasoline, alcoholCement, acrylic sweater, coal.

3. Physical properties Changes in the reaction Reaction conditions Product.

1.There is na, cl....There is also iodine in iodine-containing salt, and oxygen and other salt water will produce hydrogen, chlorine, and sodium hydroxide when electrified.

2.(2,4,6,7) (dwell: 1line: 6, 7) 3state, changes in temperature, smell (sometimes not considered), color.

1.Chlorine and sodium Table salt is an ionic crystal, and its unit cell is cubic sodium hydroxide, chlorine, and hydrogen.

2.It all seems to be related to chemistry... It is also related to human habitation and transportation.

3.Color, condition, smell...

1 cl element na element crystal Energized to obtain H2 Cl2 Naoh 2 First empty (24567) Second empty (1234567) 3 Look at the color first, then look at the state, and then smell the smell.

The chemical composition of Na and Cl table salt is NaCl, which is a very typical ionic crystal. The appearance and shape of ionic crystals are related to their lattice steps and inter-ion coordination.

h2 cl2

All 1467

The mass of the solution does not decrease, but increases. The mass of the iron nails will be lightened.

fe+h2so4=fe（so4）+h2

In the displacement reaction, the mass of the iron ions is greater than the mass of the replaced hydrogen, and the mass of the natural solution increases. Because the iron nail reacts, the quality will naturally decrease.

The mass of the iron nail will be reduced and the mass of the solution will increase.

Iron nails are dissolved in dilute sulfuric acid, and the mass is reduced.

fe+h2so4=feso4+h2↑

56 2 is injected with 56 g Fe to generate 2 g H2, and the mass of the solution is increased by 56-2 = 54 g

Fe+H2SO4=FeSO4+H2 Because the relative mass of Fe is greater than H, the liquid (FeSo4) is heavier than the original, and the nail loses Fe atoms and becomes lighter.

The mass of the liquid will be aggravated.

The mass of the iron nails will be lightened.

Iron nails react with dilute sulfuric acid to form ferrous sulfate and hydrogen, so the mass of iron nails decreases, and the liquid mass increases.

(1) Take a small amount of sample and add hydrochloric acid, if there are colorless bubbles, it proves that it has not completely deteriorated; On the contrary, it is completely deteriorated.

2) Magnetite adsorption iron powder (b) all Fe2O3 (c) both Fe(Oh)3 and Fe2O3

3) B4) take a small amount of brown powder in the test tube, add an appropriate amount of hydrochloric acid to dissolve the powder, if the solution is yellow, add a sufficient amount of NaOH solution to produce a reddish-brown precipitate, which proves that the precipitate is Fe(OH)3, so as to prove that the brown powder contains iron.

5) Select CH4 by igniting the gas and covering a small beaker with clarified lime water on the inner wall above the flame, if the lime water becomes turbid, it proves that CH4 contains carbon elements.

CH4 is selected by igniting the gas and covering a small beaker with dry cold above the flame, if there is a mist of water on the inner wall of the beaker, it proves that CH4 contains hydrogen.

NaCl solution is selected by adding nitric acid and silver nitrate solution, if there is a white precipitate generated, it proves that NaCl contains chlorine.

Let the mass of the solute in the remaining solution be x, then it will be determined by x 70=(x-4) (70-4-10) x=20

Because the solution is saturated, it is 70 x = 10 4, and the answer is 28g