When PH 12, the phenolphthalein test solution was dropped

Colourless. The discoloration of phenolphthalein ranges from (pH).

Phenolphthalein is a very weakly acidic organic acid, and the acid ions ionized by this acid are red. When the concentration of hydrogen ions is high, the ionization of phenolphthalein can be inhibited; When the concentration of hydrogen ions is low, the ionization of phenolphthalein can be promoted. The concentration of hydrogen ions is directly related to pH

pH = -LG (hydrogen ion concentration), so the amount and concentration of phenolphthalein are different depending on pH. This gives rise to different shades of red.

If the concentration of phenolphthalein is too low, of course, it will have no color; If the concentration of phenolphthalein is too high, and phenolphthalein is a very acidic organic acid, that is, a weak electrolyte, the increase of the concentration will reduce the ionization degree of the weak electrolyte (that is, the ratio of the ionized part of the electrolyte to the total amount), and the acid ion concentration of phenolphthalein will also decrease. You can't see the red color either.

Do you understand?,This is college content or high school 3 science chemistry content.,I know about Drip ...... from the competition class.Pick me to be the best, hehe.

The more I look at it, the more confused I become, in fact, the answer on the third floor is right, and the process is wrong.

The color of phenolphthalein has little to do with its concentration, mainly the pH value. The change in the color of phenolphthalein in alkaline solution is due to a change in structure (equilibrium of quinone and ketone formulas), but when the alkalinity is too strong, phenolphthalein continues to become a third structure, and this structure is colorless.

I also saw it when I studied analytical chemistry on my own in my third year of high school.

However, I suspect that pH = 12 is not very alkaline, so it is better to do an experiment on your own, it should not be difficult.

The explanation on the third floor is good, but it turns out to be wrong!

It should be red The reason for this is that phenolphthalein is an organic acid that can undergo reversible ionization and can represent hin colorless in-red + h+

When the alkalinity of the solution is large, the equilibrium is carried out in the positive direction, so it shows the color of in- and appears red; When the solution is acidic, the equilibrium proceeds in the opposite direction, so it appears colorless.

It's definitely a colorless game. I learned in chemistry competitions. The specific reason for MGCL2 must be basically correct. But if you want to know why the acid ions ionized by this acid are red, you have to refer to the theory of crystal fields. I won't talk about it here.

Red, the solution is alkaline.

Red because of the alkali and phenolic peptides occur to reflect ah.

pH greater than seven is alkaline, and the alkaline substance reacts with phenolphthalein to become alkaline.

Colorless, ahh

When the phenolphthalein indicator changes from colorless to reddish, the pH of the solution has no exact value, generally above 8. Phenolphthalein is a commonly used acid-base indicator and 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.

Phenolphthalein quickly fades from red to colorless in strong alkali, and will also change color in concentrated acid, and excessive addition of phenolphthalein dropwise in dilute acid solution causes precipitation, making the solution white and turbid. This is due to the fact that alcohol is easily soluble in water, which precipitates phenolphthalein, which is insoluble in water. The quinone or quinone type of phenolphthalein, which is very unstable in alkaline media, will slowly convert to the colorless carboxylate form; When encountering a more concentrated lye, it will immediately transform into a colorless carboxylate formula.

Therefore, when the phenolphthalein reagent is dropped into a concentrated lye, the phenolphthalein begins to turn red, and soon the red color fades and becomes colorless. Phenolphthalein turns orange when exposed to concentrated sulfuric acid.

The discoloration range of litmus test solution is 7-9, the discoloration range of phenolphthalein test solution is 8-10, the solution of pH=2 at room temperature is acidic, the litmus test solution turns red when it meets acid, and the phenolphthalein test solution is colorless when it meets acid, so at room temperature, the phenolphthalein test solution dropwise in the solution of pH=2 shows colorlessness, and the dropwise addition of litmus test solution shows red, so the answer is: none; Red

To make the phenolphthalein test solution in hydrochloric acid appear red after dropping, it means that the solution should be alkaline, so the alkaline solution should be added to neutralize the hydrochloric acid first, and then the excess solution should be alkaline, so it can be sodium hydroxide solution

Therefore, the answer is: sodium hydroxide is a solution for eliminating stove grinding and so on

Alum heating promotes Al3+ hydrolysis, Al3+ +3H2O = reversible = Al(OH)3+3H+, and the solution is acidic and does not change color.

b.Promotes CH3COO- hydrolysis, CH3COO- +H2O=reversible=CH3COOH+OH-, alkalinity is enhanced, and the color becomes darker.

It inhibits the ionization of NH3·H2O and becomes lighter in color.

It will hydrolyze H+, neutralize HCO3- hydrolyzed OH-, and the color becomes lighter.

Answer B alum hydrolysis solution is acidic, acid can not make the phenolphthalein test solution discolored, A is incorrect; Sodium acetate hydrolysis, the solution is alkaline, common hydrolysis by heating, alkalinity enhancement, darkening color, option B enhancement; Ammonium chloride solids inhibit the ionization of ammonia, the color becomes lighter, c is incorrect; The sodium chloride solid cannot affect the hydrolysis and ionization of sodium bicarbonate, and the color does not change, so the correct answer is B.

a. The acidic solution cannot change the color of the colorless phenolphthalein solution, so the option is wrong B. A few drops of phenolphthalein test solution are dropped into a colorless solution, and the solution turns the phenolphthalein red, indicating that the solution must be an alkaline solution, so the option is correct

c. The aqueous solution of the acid is acidic and cannot change the color of the colorless phenolphthalein solution, so the option is wrong D. A few drops of phenolphthalein test solution are dropped into a colorless solution, and the solution turns the phenolphthalein red, indicating that the solution must be an alkaline solution, but it is not necessarily an aqueous solution of alkali, or an aqueous solution of salt such as sodium carbonate, so the choice is wrong

Therefore, b

Phenolphthalein is an indicator, which turns red when exposed to acid and does not change color when exposed to alkali.

Purple litmus reagent, red when acid, blue when alkalin.

There are also special solutions that can be used to test a certain reagent.

Phenolphthalein test solution, discoloration range.

Light red, less than 8 colorless, greater than 10, red.

The pH test strip is light green at pH = 8.

The red discoloration range refers to the pH range in which the color of the indicator changes.

Phenolphthalein is light red in color.

At pH <10, phenolphthalein is colorless. At pH >10, phenolphthalein is red.

Other indicators have a similar phenomenon, such as methyl orange with a discoloration range of orange, a pH of red, and a pH >of yellow.

For general alkaline solution, phenolphthalein is added to appear red. However, adding phenolphthalein to a strongly oxidizing alkaline solution, such as sodium hypochlorite solution, will become colorless. What kind of situation you are asking, it is not clear.

a. The alkaline solution must be alkaline, but the alkaline solution is not necessarily the alkaline solution; Therefore, the dropwise addition of colorless phenolphthalein test solution in a colorless solution turns red, which can only indicate that the solution is alkaline, and it is impossible to determine whether the substance is alkaline, so a is correct; b. The solution contains SO42-, and the BACL2 solution is added dropwise to generate a white precipitate BaSO4 insoluble in dilute nitric acid; The solution contains AG+, and the BACL2 solution is added dropwise to generate a white precipitate insoluble in dilute nitric acid AgCl Therefore, the solution that is insoluble in dilute nitric acid is generated by adding BaCl2 solution dropwise to generate a white precipitate insoluble in dilute nitric acid does not necessarily contain SO42-, so b is correct; c. Move a test tube that collects gas close to the flame, if it makes a popping sound, it indicates that the gas is pure, so C is wrong; D. Verify whether the caustic soda solution contains Cl-, dilute hydrochloric acid can not be added to remove OH-, nitric acid should be added first, so D is wrong, so AB is selected