Masters who understand chemistry help, chemistry, masters please come in... Hurry. . .

Because my voice was indistinct, I couldn't hear what the teacher was saying, so I had to look at it – in fact, the main reason was that my English level was too far from the interpreter.

Let's talk about the flame color reaction first: some salts are added to the solid alcohol to make it contain the corresponding metal elements, from left to right, they are Li purple red, SR magenta, k light purple, Fe golden yellow, ba yellow-green, cu blue-green, CS light purple.

The first experiment was a handkerchief experiment: 2 volumes of alcohol and 1 volume of water were mixed, and when the mixed solution was ignited, the alcohol and water gradually evaporated into gas at the same time, thereby reducing the concentration of flammable alcohol vapor, so that it did not burn very violently and did not emit much heat. Due to the presence of water that cannot be burned, part of the heat also needs to be supplied with the vaporization of the water supply and the heating of the water vapor, thus consuming a large amount of heat.

The temperature of the handkerchief does not rise so high that it does not reach its ignition point, and the handkerchief does not burn.

The main reactants in the second experiment were sodium carbonate and hydrochloric acid, possibly with the addition of soapy water to enhance the foaming effect.

The third one, I'm not sure, it's a bit like liquid carbon dioxide, but if it were, the lectern should be able to see the fog, and the teacher should wear rubber gloves to avoid frostbitten hands, doubtful!

The fourth is the flame reaction.

The fifth phenomenon is not clear, but only the formation of gas, which causes the liquid level of the inverted huge test tube filled with liquid to plummet, is probably nothing more than an example of atmospheric pressure.

The sixth and seventh are hydrogen combustion occurs**, but the test tube is larger, and the seventh uses ** to beat the confetti.

Needless to say, the last one is set off with fireworks during the holidays.

The flame color reaction is a reaction in which certain metals or their volatile compounds take on the characteristic color of a flame when it burns in a colorless flame. Some metals, or their compounds, can give a special color to the flame when burned. This is because when the atoms of these metallic elements receive the energy provided by the flame, their outer electrons will be excited to the higher energy excited state.

The outer electrons in the excited state are unstable and have to transition to a lower energy ground state. The outer electrons of atoms of different elements have ground states and excited states of different energies. In this process, electromagnetic waves of different wavelengths are generated, and if the wavelength of this electromagnetic wave is in the visible wavelength range, the characteristic color of this element is observed in the flame.

The first burnt knife may be ethanol with a higher water content, and the money is still wet after the ethanol is burned quickly.

The second should be the foam extinguishing agent principle: 6NaHCO3, deca2(SO4)3, 2al(OH)3deca3Na2SO4, deca6CO2

One of them is that the red-brown gas that is released may be the reaction of copper and concentrated nitric acid to form NO2**, and the two do not know what kind of combustible gas they are, according to our middle school chemistry demonstration experiment, it may be hydrogen, and our teacher demonstrated it, using paper cups.

The last one could be a thermite reaction.

The bright color reaction should be a flame color reaction.

1，co2

2. The statements about chlorine are all correct Copper and chlorine ignite Cu+Cl2=CuCl2 Chlorine and hydrogen ignite H2+Cl2=2HCl, chlorine and water disproportionate Cl2+H2O=HCl+HCl

3, b is potassium manganate c is manganese dioxide d is oxygen e is hydrogen peroxide f is water I can't choose the answer to the wrong question in the back, please be smart.

A candle is essentially a mixture of hydrocarbons, only carbon and hydrogen, the water generated by combustion is liquid at room temperature and aluminum reaction with oxygen will only produce alumina, which is a solid with a high melting point Phosphorus reacts with oxygen to form phosphorus pentoxide, which is also a solid Iron is also similar, forming iron oxide, which is solid, so choose A

If NiFe O is a reactant, the mass will inevitably decrease after the reaction, and the reaction of carbon dioxide to oxygen is obviously not easy to occur (but it is possible), and it is the function of the catalyst to make the reaction that is not easy to occur, so C is chosen

According to the title, to collect 4 percent of the gas is one liter, and according to m=v, the mass of oxygen obtained is, that is, grams of oxygen.

This is just a personal opinion, and we apologize if there is a mistake.

co2；Right, right, right, right, right, right, right, A is kmno4, b is k2mno4, c is mno2, d is o2, e is h2o2, f is h2o, wrong is a, there is liquid generation is a, in the process cm=

Carbon dioxide.

Potassium permanganate, manganese peroxide, manganese dioxide, oxygen, concentrated sulfuric acid, water AA

Conservation of charge: Cations and Ions = Anions and Ions.

That is, H+ +NH4+ = Cl- +OH-NH4ClCl in Cl- completely exists as an ion, and NH4+ becomes NH4+ and NH3·H2O

NH4+ +H2O – NH3·H2O + H+NH3·H2O in NH3·H2O + H2O – NH4+ +OH-

The solution is alkaline and the ionization is greater than the hydrolysis of NH4+.

cl->nh4+>oh->h+

The test points of this question are conservation of electric charge and hydrolysis.

Regardless of whether it is hydrolyzed or not, ammonium chloride ions, hydrogen ions and hydroxide ions are present in ammonium chloride solution. The solution must show electrical neutrality, while the solution shows neutrality, then c(h+)==c(oh--).

According to the conservation of charge: C(H+)+C(NH4+)==C(OH--)C(Cl--)

C(c(NH4+)==C(Cl--)

When considering hydrolysis, the ammonium concentration is slightly smaller than the chloride ion concentration.

Therefore, there is c(cl )==c(nh4+) c(h)==c(oh).

Here's how:

1.Prepare a complexing solution of i2 and starch (a certain concentration, must be accurate), take the standard solution and sweep the maximum absorption peak on the photometer.

2.Take the standard solution for dilution; Prepare a solution of 1 5, 1 25, 1 75, 1 150, 1 300 (you can choose the dilution factor according to your needs).

3.Set the spectrophotometer at the wavelength where the absorption is maximum.

4.Absorption is determined at this wavelength for standard solutions of different concentrations5Make a working curve of concentration vs. absorption (A=ABC)6, and then measure the absorption of the complex solution of iodine and starch remaining from your above experiment at this wavelength.7 The corresponding concentration is found (or calculated) by the working curve.

At the end of the experiment, I have a question, is the complex of iodine and starch stable? How much I2 or starch does it affect absorption? , which solves the above doubts, if there is no impact.

This method is reliable.

Hello Principle of calibration of formaldehyde solution (iodometry) :

In the formaldehyde solution, after adding lye to make the solution alkaline, add a certain amount of excess iodine standard solution, and the formaldehyde is oxidized

hcho + i2 + 3naoh = hcoona + 2nai + 2h2o

Leave for 5 minutes, after the reaction is complete, acidify the solution with hydrochloric acid or sulfuric acid, use starch as an indicator, and titrate the excess I2 with Na2S2O3 standard solution

i2 + 2na2s2o3 = 2nai + na2s4o6 content is about that, just add details