High School Chemistry Ask for the answer must!!

1) cl2+2br-=2cl-+br2

2) B: Colorless to blue.

3) Absorb unreacted chlorine gas to prevent environmental pollution. ci2+2naoh=nacl+naclo+h2o

4) cl2>br2>i2

Answer: 1, cl2+2br- =2cl- +br2

2. Cotton ball B turns blue.

3. Absorb excess chlorine to avoid polluting the air Cl2+2NaOH=NaCl+Naclo+H2O

4、cl2>br2>i2

Analysis: The first thing to do is to analyze the question stem:

a. Bromine ions can react with chlorine to form chloride ions and bromine elements;

b There are iodine ions and starch, iodine ions can be oxidized to iodine by chlorine and bromine, and iodine will produce a blue chromogenic reaction with starch;

c is that cold water can absorb halogens in small amounts, and cotton balls soaked in cold water have stronger retardation, and low temperature will condense steam;

d is that the sodium hydroxide solution can react with halogens in large quantities to produce sodium halide and sodium hypohalide.

Then look at the specific topic:

1. Write the ionic reaction formula of bromine ion and chlorine as required;

2. The air flow through A will be converted into bromine elemental vapor, but bromine can also oxidize iodine ions to iodine element, so there will be iodine elemental generation on B, and there will be a blue reaction with the starch contained in B, that is, "cotton ball B turns blue";

3. Because bromine and iodine vapor will be condensed and blocked by C cold water cotton balls, it is an excess chlorine gas flow that comes out of the reaction space, and chlorine is toxic and cannot be allowed to be discharged into the atmosphere, so the use of sodium hydroxide solution ** chlorine is an economical, practical and efficient choice in the laboratory;

4. The experimental design is not too good, and it is easy to have accidental situations, but ideally, the chlorine gas flow will be transformed into bromine gas flow through A, and the bromine gas flow will produce iodine element blue when it meets starch, which can reflect the strongest oxidation of chlorine element, the second highest bromine element, and the weakest iodine element.

The answers are a and b.

a、2al+6hcl==2alcl3+3h2↑2al+3cl2==2alcl3

b、mg+2hcl==2mgcl2+2h2↑mg+cl2==mgcl2

c. Fe reacts with Cl2 to form FeCl3, because Cl2 is highly oxidizing and will oxidize Fe to +3 valence.

2fe+3cl2==2fecl3

Fe and HCl form FeCl2, because HCl is weakly oxidized, only Fe can be oxidized to +2 valence.

fe+2hcl=fecl2+h2↑

D. Cu reacts with Cl2 to form CuCl2, and Cu does not react with HCl.

AB and FE have two different methods of valence, and Cu does not react with hydrochloric acid.

Let the mass of mg be x al and the mass of y and list the equation 1 x + y = the mole of the gas as.

The relative atomic masses of mg and al are 24 and 27 to give the second equation x 24+y 27=

Simultaneous equations are used to find the solution.

The amount of a substance with x= y=mg is.

The amount of the substance of al is:

The mass fraction of al is:

The mass fraction of mg is:

In the reaction, only hydrogen atoms are consumed, Cl is not consumed, and it is still 500ml after the reaction, so the concentration of Cl- remains the same as the concentration of HCl.

Simultaneous equation solving is a very common technique, remember.

mg:24;al:27

From the equation mg + 2HCL = mgCl2 + H22AL + 6HCL = 2ALCL3 + 3H21molMG to transfer 2mol electrons, 1molAL to transfer electrons 3mol MG - 6mol E- - 3mol H22mol Al - 6mol E- - 3mol H2 After clarifying the above, you can start to do it Let the mass of mg be 24xg, and Al is 27yg.

24x+27y=formula).

x + two-thirds y = formula).

Then solve x, y one or two questions will come out

It has been emphasized in the question that the volume does not change, and the ionic reaction Cl- in the solution is an irrelevant ion, so the amount and concentration of Cl- in the solution after the reaction is the same as the concentration of hydrochloric acid before the reaction, which is 2mol l

o( o If I'm wrong, remember to ask me to correct it.

1.It is converted from chemical energy to electrical energy.

The chemical reaction of the galvanic cell is a redox reaction.

Option zinc is more reactive as a negative electrode, so soluble.

The positive electrode of option b is the cation to get the electron, so it is the hydrogen ion that gets the electron to produce hydrogen.

c Option current flows from the positive to the negative electrode.

Option d electrons flow in the opposite direction to the current.

3.The anions move towards the negative electrode.

The first stage of electron outflow is the negative electrode.

What occurs at the negative electrode is an oxidation reaction that loses electrons.

The first stage of electron inflow is the positive electrode.

What takes place at the positive electrode is a reduction reaction to gain electrons.

In zinc-copper batteries, zinc is more active as the negative electrode, and copper is.

This is a simple chemical galvanic cell problem. In galvanic batteries, zinc with strong reducing properties is used as the negative electrode, and another metal, copper, is used as the positive electrode. Then the direction of the current must be from the copper of the positive electrode, flowing to the zinc of the negative electrode, the movement of electrons is exactly the opposite of the direction of the current, from the zinc flowing to the copper through the wire, the zinc of the negative electrode in the galvanic cell loses electrons and continues to dissolve, generating zinc ions in the solution.

The highly oxidizing hydrogen ions on the copper electrode, which is the positive electrode, are reduced to form hydrogen gas.

c Zinc is more active than copper, as a negative electrode, reacts with sulfuric acid to generate hydrogen, the mass decreases, copper is used as a positive electrode, no reaction occurs, and hydrogen is produced near the copper electrode. The current flows from the positive electrode to the negative electrode, and the electrons flow from the negative electrode to the positive electrode, so C is chosen

It's too difficult. I really can't calculate it.

a.Putting NaOH in water is a liquid solution of , which is conductive BThe neutralization reaction is common to the H+ reaction and is left with C

Neutralization reaction A total of 1mol of H+ reaction is lost and D. remainsNo reactivity The concentration of the electrolyte increases and the electrolyte becomes stronger.

The biggest change is a

The key to this question is that the "change" before and after the change A is the largest, and the change B is the second

Choose A, BCD are both strong electrolytes, and there is little change. A hardly conducts electricity, so A changes the most.

The answer is that the concentration of solution D and A decreases, and the neutralization reaction occurs between B and C, and D does not react, and the concentration of anions and cations in the solution increases.

The answer is a

The conductivity of a solution depends on the free movement of ions.

The number of freely moving ions in tap water is very small, which increases significantly when NaOH is added to the formation solution, while the other three Bunsen have many free moving ions, and the number of them does not change much after the addition of NaOH. Gu Xuan A