Ask junior high school chemistry questions, ask for advice, and expect an analysis process

1. The sodium carbonate solution is alkaline, all the weak acid and strong alkali saline solutions are alkaline, 2. Mg(OH)2 al(oh)3 insoluble alkali, there is no way to ionize OH-ions, and the indicator cannot change color.

3. The indicator, when describing, it is necessary to say that the purple solution turns red (blue) or the colorless solution turns red (corresponding to litmus reagent and phenolphthalein solution respectively).

When I reach high school, I will learn about strong and weak salts and strong and weak alkali salts.

Common strong alkali weak salts are: sodium carbonate, sodium acetate, sodium phosphate, sodium acetate (note that NaOH is a strong base, not a salt).

Strong acids and weak alkali salts are: copper sulfate, iron chloride, ammonium chloride, aluminum chloride, iron sulfate.

The insoluble alkali is easy to decompose when heated, and it does not react with the salt solution, and (cannot) change the color of the indicator.

Common insoluble bases are: [blue] Cu(OH)2

Reddish-brown] Fe(OH)3

White] Mg(OH)2, AI(OH)3 Mn(OH)2 Zn(OH)2 soluble and insoluble bases all have the general properties of bases:

1. Effect with the indicator: the alkali solution can make the purple litmus test solution blue and the colorless phenolphthalein reagent red.

2. It reacts with acidic oxides to form salt and water.

3. React with acid to form salt and water.

4. React with certain salts to form new salts and new bases.

The insoluble alkali is not obvious, if there is no discoloration of the acid-base indicator, can not meta-decompose with salt, etc., the insoluble alkali is easy to decompose when heated).

CuSO4 (strong acid and weak alkali salt. acidic).

Cu(OH)2, Fe(OH)3 (non-ionizing in solution, no discoloration) indicator, acid, alkali solution.

Give points.

17. The solution obtained by AB also contains impurities Na2CO3C, and the solution obtained by C also contains impurities Ca(OH)2

d The main substance cao also participated in the reaction.

18. When magnesium bars and iron wires of equal quality are reacted with sufficient amounts of dilute sulfuric acid respectively, the reaction rate of magnesium bars is greater than that of iron wires, and the reaction is complete.

The mass of the gas generated after is also greater than that of the gas produced by the same mass of iron, and the representation in the image should be that the mg and fe are interchanged.

It's the right thing to do.

It should be B, because magnesium is more active than iron, and the reaction with dilute sulfuric acid should be faster than iron, and the same mass of magnesium and iron reacts with dilute sulfuric acid, magnesium produces more gas, and from the diagram, magnesium reacts slower with dilute sulfuric acid than iron, and produces less gas than iron, so it is not true.

From known, available.

o Atomic mass: (m-n)kg

S atomic mass: n - 2(m-n) = (3n-2m)kg takes 1 32 of the mass of sulfur atom as the atomic weight criterion, so the relative atomic mass of s is 32

Oxygen is: 32 3n-2m) m-n) 32(m-n) (3n-2m).

SO3: 32 3 32 (M-N) (3N-2M) is divided and simplified to 32m (3N-2M).

18 d, matter is made of elements, it cannot be said that it is composed of atoms19a, false, although the number of h atoms in the molecule is the largest, but because the relative atomic weight of h atoms is small, the mass fraction is not the largest.

B, True C, False, this is not the mass ratio, but the number of atoms than D, False, in the molecule, can only contain atoms, 20, as can be seen from the table, the larger the relative molecular weight of the gas, the easier it is to be adsorbed The relative molecular weight of Cl2: 71, the relative molecular weight of CO2: 44

Relative molecular weight of O2: 32

Relative molecular weight of N2: 28

Relative molecular weight of H2: 2

d. Comparing the data of the five gases in the table, the larger the relative molecular mass of the gas, the easier it is to be adsorbed

Upstairs is very accurate, let me correct you 26 questions, the phenomenon (2) should be the balloon expansion, because carbon dioxide reacts with calcium hydroxide, consumes carbon dioxide, and makes the air pressure in the bottle smaller, the equation is CO2 + Ca(OH)2=CaCO3 + H2O

27 questions, you should pay attention to the common black solids in junior high school are carbon, copper oxide, ferric tetroxide, manganese dioxide, and iron powder.

The common red solids, metal copper and rust (ferric oxide), the breakthrough in this problem is the red elemental E, E is copper, and B is a copper compound. So here is the reaction of the reducing agent C and CO to reduce cuo.

1) C+2CuO==High Temperature==2Cu+CO2 So it's not a chemical reaction.

Cuo+CO==Heating==Cu+CO2 So it is not a chemical reaction.

2CO+O2==Ignition==2CO2 So is a chemical reaction.

C+O2==Ignition==CO2 So is a chemical reaction.

Therefore, the chemical reaction that belongs to the chemical reaction is:

2) Reaction equation: C + 2Cuo = = High temperature = = 2Cu + CO2.

3) C; Armor.

Hope: Pure hand-hitting. Good luck with your studies

I'd love to talk to you, but what is the problem?

2) C+2CuO===2Cu+CO2 (conditions: high temperature, carbon dioxide is a gas, to mark the arrow).

3) B A.

As shown in the figure, the water vapor produced when the water in the flask is boiled into the test tube A, and the test tube A is placed in the container B containing cold water, and after a period of time, the phenomenon produced in the test tube A is observed that there are small water droplets on the wall of the test tube, which is because the water vapor liquid is liquefied by hand At the same time, the indication of the thermometer C is increased, and this experiment shows that the heat should be released in the process of changing the state of matter

Analysis: Boiling is a violent vaporization phenomenon, which can produce a large amount of water vapor, which will liquefy and exothermic to form small water droplets when cooled; When the temperature of the cold water absorbs heat, the temperature increases, and the thermometer that measures the temperature of the liquid object increases

The last one is 2