Puzzled chemical problems, chemical problems, incomprehensible solutions

After dissolving NaCl and Kno3 in water, there is no potassium nitrate or sodium chloride in the solution. Because what is present in the solution are Na+, Cl-, K+, No3-. In the process of evaporating water, when the water evaporates to a certain time, NaCl crystals precipitate, and the precipitated crystals are generated.

So at this point the metathesis reaction takes place. It's just that the reaction is not complete, and the solution is still a solution containing the above ions. Of course, you can't completely evaporate the solution, which is a mixed crystal containing the above ions.

That is, if the following substances with an equal number of particles are dissolved together in water, the solution obtained is exactly the same

NaCl with KNO3, NaNO3 and KCl.

The crystals obtained by evaporating the above solution are also the same.

Haha, they are not reacting, indeed, because they do not meet the conditions for metathesis reactions. They are all strong electrolytes that are found in water in the form of chloride, nitrate, potassium, and sodium ions (which you will understand as a freshman in high school). As for what happens after evaporation, it depends on their solubility at different temperatures (I don't know the exact data, you can check it yourself on the Internet).

You should be a junior high school student, so I wish you all the best in the high school entrance examination.

Not reacting. Because they are all ions when they dissolve in water.

Different substances have different solubilities.

See which substance reaches saturation precipitation first.

Here's an example. Potassium chloride and sodium nitrate are dissolved together in an appropriate amount of water.

In solution is K+ Na+ Cl- NO3-

Nano3 solubility (s) = 21 g is assumed

s(nacl)=18g

s(kcl)=20g

Then in the process of evaporating the solution, NaCl is precipitated first.

It's hard to understand.

Haha, this question is good, note that they are all ions, and they are not simple compounds after dissolution, and the mutual composition of ions will form different substances, which is related to the physical and chemical properties of the compounds they combine to form (solubility, heat resistance, volatility, ion electron distribution, charge charge of two ions, etc.), which is more complicated.

It does not react and coexists in the form of ions in solution, due to different solubility of precipitates.

Chemical reactions can be analogous, which are naturally different kinds of reactions.

Different reactants, the different reaction conditions are generally related to the properties of the reactants themselves.

Example: Reaction of halogen elements with hydrogen.

Fluorine and hydrogen can be used in dark places, chlorine and hydrogen can react by light, and bromine can react with hydrogen heating

Argon in 1 may act as a catalyst.

The one in 2 is the reactant, so of course you have to write it out.

Why are they all sodium oxide, alumina, instead of sodium oxygen, aluminized oxygen is customarily put the negative valence behind, except for ammonium and a few.

Carbon negative tetravalent only and h carbon has a variety of valence states Upstairs nonsense, oxygen and hydrogen have many other valences. NaH minus monovalent Na2O2 oxygen minus monovalent!!

Oxygen is generally minus bivalent, some special ones will be encountered later, you must know that you should find me a good chemical force to find stability Unstable substances such as hgo are easy to decompose.

Whether it's the combination of two elements, their purpose is to achieve a steady state, and the purpose of all reactions to chemistry is to achieve a stable state.

Carbon is generally normal, and it is easier for the oxygen element to get 2 electrons to become 2 valence. As for why it is called sodium oxide, alumina is a naming rule, and there is no reason to say it. Many of the organic compounds are not in a steady state.

Maybe they are all unstable, and they have to be heated when CO becomes CO2, so with oxygen, the oxidation valency changes.

Yes, if there is too much acid, the solution will be acidic, and the acidic solution is also colorless phenolphthalein does not change color.

However, the red color at the beginning gradually becomes colorless, indicating that the hydroxide ions are gradually decreasing, because of the reaction with hydrogen ions.

The color development of phenolphthalein does not require hydrogen ions, it is the result of phenol and carboxyl double negative ions in phenolphthalein, as long as the proton of phenolphthalein is removed, it can be colored.

In the aqueous solution of sodium hydroxide, because it is alkaline, phenolphthalein is colored, but phenolphthalein is colored due to the presence of alkali of hydrogen that removes it, so if hydrogenation makes more hydrogen ions, it cannot fade because there are fewer hydroxides.

Solution: Preparation of sodium hydroxide solution and hydrochloric acid solution;

Use a dropper to take a sodium hydroxide solution and add 25 drops in a small test tube, add 3 drops of phenolphthalein, and the solution turns red;

Use a dropper to take the solution hydrochloric acid solution, add it dropwise to the red solution of sodium hydroxide, and an acid-base reaction occurs in the small test tube to generate sodium chloride and water. When there is still sodium hydroxide left, the solution is alkaline, and phenolphthalein also shows red; When the dropwise is added to the red color just fades, the sodium hydroxide in the solution is neutralized, indicating that the reaction is complete.

Put it in sodium hydroxide first to make it red, put it in phenolphthalein hydrochloride to become colorless. It proves that sodium hydroxide and hydrochloric acid react??? yes, what about the excess acid, you just say that there is no reaction, as long as the phenolphthalein fades, it proves that there are fewer hydroxide ions, which is the reaction.

There is a discoloration pH value that is not just added with hydrochloric acid.

Water is a weak electrolyte, and ionized hydrogen ions and hydroxide cannot coexist in large quantities.

That's right, but phenolphthalein turns red when exposed to alkali, unlike litmus.

1.First of all, from its chemical formula, we can know that the unsaturation = 5, 9 carbon or more, and the unsaturation above 4 generally contains benzene ring, and the benzene ring has accounted for 4 unsaturation, and there is one unsaturation left.

2.Insoluble in water, dilute hydrochloric acid and dilute sodium bicarbonate solution, but soluble in dilute sodium hydroxide solution, indicating that its acidity is weaker than that of carbonic acid, indicating that it contains phenolic hydroxyl groups.

3.Continue to look, the solution is cooled and acidified to obtain a precipitate B (C7H6O3), the unsaturation of B is still 5, and the alkali is added first and then acid is added to become precipitated, which is obviously a carboxylic acid. , which is very consistent with the dissolvable sodium bicarbonate in the back.

Obviously, A is an ester structure, which is why A is insoluble in dilute sodium bicarbonate solution, but after hydrolysis, acidification into B can dissolve sodium bicarbonate.

4.Looking at it again, B can interact with ferric chloride solution to show purple color, indicating that it contains phenolic hydroxyl groups, so the structure of B is probably known, that is, there is a hydroxyl group and a carboxyl group on the benzene ring, but it is not known whether these two groups are ortho, meta, or para.

5.That last sentence is crucial: steam distillation is possible in acidic media.

B knows that it is carboxylic acid and phenol, generally speaking, its boiling point should be higher than water, but it is the last sentence that shows that its boiling point is lower than water, what is the reason, drawing its possible three structures, it can be seen that because the hydroxyl group and the carboxyl group are in the ortho position, the formation of intermolecular hydrogen bonds, but its boiling point is lower than that of water. So b is o-hydroxybenzoic acid.

6.Then a is ethyl o-hydroxybenzoate.

To do organic inference questions is to guess a little and look at it coherently.

I'm not very good at the last condition, but I'll give you one as a general idea.

First of all, calculate the unsaturation of A, which is 5, according to the fact that B can turn purple, it means that there is a phenol group in B, so there must be a benzene ring (4 unsaturations) and a double bond in A, and because it cannot be an acid (otherwise it will react with sodium bicarbonate), there is an ester group.

Looking back at B, B can react with sodium bicarbonate to form CO2, so B is an acid, and B has only 7 C's, so it is a formic acid group.

On the whole, there is a benzene ring, a phenol group, and an ester group of formate in a.

The rest may have to be judged by the boiling point (using the third condition).

Eh......It's been a long time since I've done chemistry, and I'm unfamiliar

b. It can be dissolved in sodium bicarbonate solution and release gas; B reacts with ferric chloride solution to show purple color, indicating that B contains phenolic hydroxyl group and carboxyl group, which can be known in the combined chemical formula, A should be its ester.

A is ethyl o-hydroxybenzoate, O-C6H4 (OH) Cooc2H5

B is o-hydroxybenzoic acid, O-C6H4(OH)COOH

It's not that difficult (at least in our school it's a general question).

An aqueous solution can make the moist red litmus paper blue: only NH3 is consistent in high school chemistry.

A + oxygen b, b is either water or NO; and b can also react with oxygen, then b is the no reaction equation: 4nh3 + 5o2 = 4no + 6h20 from the above we can see that their common element is n.

Then NO2 reacts with oxygen to form NO2(C), and NO2 reacts with water to form HNO3(D).

The dilute solution of D can make the blue moist litmus test paper red, D is an acidic substance, and the introduced Hno3 meets the conditions and is established.

The topic is not difficult, just think a little about finding a breakthrough.

An aqueous solution can make the moist red litmus paper blue, so A is NH3A + oxygen B, so B is No 4NH3 + 5O2 = 4NO+6H2OB + oxygen C, so C is NO2 2NO+O2=2NO2C + water D, so D is HNO3 3NO2+H2O=2HNO3+NO3+NO

a：nh3a-b：nh3+o2=no+h2o

Study hard and make progress every day.

The meaning of the title is to let you get rid of the electrolyzed water... Option B is the oxygen-producing acid type.

Pure water itself does not conduct electricity, you have to add other substances to make it more conductive in order to electrolyze water better and faster. In order to enhance the conductivity of water electrolysis, substances that are not electrolyzed by themselves or whose electrolytic products are the same as water should be added.

The above options anion are all OH- after discharge.

The discharge sequence of cations is Cu2+, H+, Na+, K+.

Only Cu2+ of CuSO4 will produce Cu during electrolysis before hydrogen ions, so B is chosen

Since the conductivity of pure water is very poor, electrolyte should be added to electrolyze water to increase its conductivity. The added electrolyte should not be electrolyzed, so B cannot be used, otherwise the CU on the cathode will precipitate during electrolysis.

Personal opinion: Cu and OH are combined, and the electron transport efficiency is low at the same ion concentration

I don't know if it's correct, but I hope it can guide your thinking

The above four substances are all electrolytes, and electrolytes can increase the conductivity of the solution (some substances are not necessarily electrolytes but their solutions can also conduct electricity, such as chlorine water, Cl2 is not an electrolyte), because CuSO4 will also be electrolyzed in water, so it is not suitable to be added.