When the acidic solution and the alkaline solution coexist the two do not react , phenolphthalein i

First of all, in middle school chemistry, it is impossible for common acids and common bases not to react together, there is no reason for this? That's how nature is arranged. If I had to explain why, I'm afraid I'd have to use my university knowledge.

This premise must be clarified before explaining the problem, and if this joint is not clear, there is no way to talk about the problem. Well, strong acids and strong bases are definitely going to react, so we can use indicators to detect whether the reaction is completely carried out.

If acid is added to the alkali solution, we add phenolphthalein to the original alkali solution, at this time the solution is red, when hydrochloric acid is added, the hydrochloric acid reacts with sodium hydroxide, and the sodium hydroxide is consumed, so the alkalinity weakens, and the red becomes lighter. When the two happen to react completely, we think that at this point the phenolphthalein happens to change from red to colorless. This discoloration is abrupt, so it can be seen with the naked eye with great precision.

If a base is added to an acid, then the principle is the same. At this point, the color changes from colorless to reddish.

As for what the landlord said, "But if there is too much HCL and the alkalinity is diluted, then even if the two do not react at this time, the color will change!" "Can I understand that the landlord is talking about dilution? Then I can calculate for the landlord that the discoloration range of phenolphthalein is pH8-10.

If we want to dilute a 1L sodium hydroxide solution from 13 to 8 to make it change from red to colorless, then we need to add 10,000L to distilled water. So the landlord should not think about the problem from this point of view.

In fact... I think... It's impossible not to react when put together ... Which excess is which nature ...

First. There are NAOH and phenolphthalein in the container, which are red at this point, right.

Add HCl (even if it doesn't react) then the mass fraction of the acidic substance in the container becomes larger, the phenolphthalein naturally becomes lighter, and finally becomes transparent.

But... These two things will definitely react.

The discoloration range of phenolphthalein is that phenolphthalein can only detect alkalis and not acids.

The phenolphthalein indicator is added to a colorless aqueous solution, which is colorless, and the acidity and alkalinity of this solution is d

The concentration of methyl orange is an aqueous solution with a red pH (yellow), which is suitable for titration between strong acids and strong bases and weak bases.

When titrating acid solution with NaOH, only pure change can be used phenolphthalein as an indicator as a side judgment. （）

a.That's right. b.Mistake.

Correct answer: B

As a commonly used acid-base indicator, phenolphthalein is widely used in acid-base titration processes. Under normal circumstances, phenolphthalein does not change color when exposed to acid solution, does not change color when exposed to neutral solution, and turns red when exposed to alkali solution. Used as an indicator in the laboratory, the discoloration range pH value, from colorless to red.

Therefore, phenolphthalein can only test the base but not the acid.

The neutralization reaction of acid and base is a reaction in which acid and base exchange components with each other to form salt and water.

Before the reaction, the phenolphthalein test solution was dropped into the alkaline solution, and the solution was red. Slowly drop into another reaction solution, and when the neutralization reaction proceeds to just complete the reaction, the red color of the solution is observed. This can indicate the progress of the neutralization reaction, or it can indicate the completeness of the reaction.

However, it is not possible to say whether too much acidic solution is added to make the test solution acidic. (A small amount of phenolphthalein test solution cannot make the acidic solution colored).

What reaction will occur between ** acid and base, a student gradually added dilute hydrochloric acid to the sodium hydroxide solution (with a few drops of phenolphthalein solution), when the red color of the solution just receded, 50g of dilute hydrochloric acid was used, and the mass of the solution after the reaction was measured to be 90gFind the quality of the solute in the solution obtained after the reaction.

Analysis: After this reaction, the solute in the solution is NaCl, the mass fraction of NaCl is required, the mass of the solution is known, and we must find the mass of the generated NaCl.

After the reaction is given to xgnacl, then:

naoh + hcl = nacl + h2o* 50g xg

Get: (50g) = xg: x =

w(nacl) = =

A.........

Shows if a chemical reaction has occurred, and discoloration if it does.

Purple litmus test solution and colorless phenolphthalein test solution are common acid-base indicators, purple litmus test solution turns red when exposed to acid, and turns blue when exposed to alkali; The colorless phenolphthalein test solution does not change color when exposed to acid, and turns red when exposed to alkali

So the answer is: red, no color

The purple litmus solution turns blue when exposed to alkali, and the colorless phenolphthalein solution turns red when exposed to alkali

Therefore, fill in: blue; Red

1) The acid-base neutralization reaction occurs between sodium hydroxide solution and dilute hydrochloric acid, and the acidity and alkalinity of the solution change with the progress of the reaction.

2) During the experiment, Hua Xue found that the solution changed from red to colorless, which does not mean that the solution is neutral, because both acid and neutral substances make the colorless phenolphthalein not change color;

3) [Conjecture hypothesis] Conjecture wheel Sun Zheng: The solution is acidic, and it is a mixed solution of hydrochloric acid solution and sodium chloride solution

Wu Li thinks that the conjecture must be wrong, and it must be wrong, because the solution is alkaline, the phenolphthalein solution is red, and the solution Lasong cannot be colorless

**Experiment] Take samples, add zinc particles to the solution (reasonable enough), zinc particles react with dilute hydrochloric acid to generate hydrogen, and see that bubbles are generated

Conclusion and Reflection] According to the signs of the experiment, it can be concluded that the solution in the experiment is acid excess

Therefore, the answer is: (1) It is convenient to observe the phenomenon during the experiment

2) incorrect; Both acids and neutral substances make the colorless phenolphthalein not discolor

3) hydrochloric acid solubilization; sodium chloride solution; ②；The solution is alkaline and the phenolphthalein solution is red

**Experiment] Zinc granules (reasonable enough); There are bubbles generated

Conclusion and Reflection] The phenomenon and the conclusion must be consistent to be right).

a. The caustic soda solution is alkaline, which can make the phenolphthalein test solution red, correct;

b. Dilute sulfuric acid is acidic, and can not change the color of phenolphthalein test solution, wrong;

c. Dilute hydrochloric acid is acidic, which cannot change the color of the phenolphthalein test solution, which is wrong;

d. The salt water is neutral, and the phenolphthalein test solution cannot be discolored, which is wrong;

So choose A