2022年高中化学22个易错知识点 .pdf

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1、【化学】高中化学22个易错知识点（ chemical high school chemistry 22 fallible points）1, hydroxyl is hydroxyl It looks like a whole of OH. In fact, the hydroxyl group is a group. Its only a part of the material structure. It doesnt ionize. Which is a hydroxyl group of atoms, it is an anion, or strong or weak can ioni

2、ze out. So, is not equal to the hydroxyl hydroxyl. For example, the OH in C2H5OH is hydroxyl and will not ionize; two OH in sulfuric acid are also hydroxyl groups. As we all know, sulfuric acid can not ionize OH-. In NaOH, Mg (OH) 2, Fe (OH) 3, Cu2 (OH) 2CO3 in OH is the ion, ionization can come out

3、, so here called hydroxyl. 2, Fe3+ ion is yellow As we all know, FeCl3 solution is yellow, but does not mean that Fe3+ is yellow? No The alkali Fe (OH) 3 of Fe3+ is a weak base, and the salts synthesized by its binding with strong acid ions will hydrolyze to produce reddish brown Fe (OH) 3. Therefor

4、e, the concentrated FeCl3 solution is reddish brown, and the average concentration is yellow, which in the final analysis is caused by the hydrolysis of Fe (OH) 3. The real Fe3+ ion is mauve rather than yellow. Add Fe3+ solution to excess acid to inhibit hydrolysis, yellow will fade. 3, AgOH water d

5、ecomposition 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 1 页，共 10 页I find many people say so. In fact, the AgOH in the solubility table is -, which is considered to be water decomposition, but it is not. But the AgOH has a poor thermal stability and can be decomposed at room temperature, so the A

6、gOH is decomposed immediately after metathesis, so that AgOH does not exist at room temperature. Water has nothing to do with it. If this operation is performed at low temperatures, the white precipitate of AgOH can be obtained. 4, polybasic oxygen acid, specific is a few yuan acid, see acid in the

7、number of H. What can the number of H+ polybasic ionization, is to see its structure in the number of hydroxyl groups, the hydroxyl hydrogen is not non ionizing out. Such as phosphite (H3PO3), it looks like there are three H, it seems to be three yuan acid, but its structure is that there is a H and

8、 a O, respectively, and the central atoms are directly linked, but not a hydroxyl. There are only two O and H that make up hydroxyl groups. Therefore, H3PO3 is a dicarboxylic acid. Of course, there are other factors to consider, such as Lewis acid, H3BO3 can not be explained here. 5, acid salt and a

9、cidic solution? On the surface, the acid salt solution is acidic, but it is not. In the end what is salt, to discuss the situation, when the ionization degree is greater than the degree of hydrolysis, acidic, when the degree of ionization is less than the degree of hydrolysis, alkaline. If this is a

10、 strong acid salt, because it produce a large number of H+, and anion hydrolysis, so the 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 2 页，共 10 页acidic acid acid salt solution. But the weak acid salt, then compare it to produce the H+ capacity and the degree of hydrolysis of the anion. If the degre

11、e of hydrolysis of the anion is greater (e.g., NaHCO3, NaHS, Na2HPO4), the solution is alkaline; conversely, if the anion has a stronger ability to ionize H+ (e.g., NaH2PO4, NaHSO3), the solution is acidic. 6 and H2SO4 have strong oxidizing property Thats not right. Just add a thick word in the fron

12、t. Thats right. Concentrated H2SO4 exists in the form of molecules, its oxidation is reflected in the overall molecules, the H2SO4 in S is +6 valence, easy to get electrons, so it has strong oxidation. The oxidation of dilute H2SO4 (or SO42-) is almost no (even H2S is not oxidized), much less oxidiz

13、ed than that of H2SO3 (or SO32-). It also shows that the oxidation of the nonmetallic oxo radical is stronger than that of the high valence state, and the acidity of HClO is similar to that of HClO4. Therefore, when H2SO4 has strong oxidation, it must be rigorous, with thick in front. 7 hydrochloric

14、 acid is commonly known as hydrogen chloride It seems that both of them have the same chemical formula, which may lead to misunderstandings. Hydrochloric acid is commonly known as hydrogen chloride. In fact, hydrochloric acid is a mixture, a mixture of hydrogen chloride and water; and hydrogen chlor

15、ide is a pure substance, which is fundamentally different. Hydrogen chloride, dissolved in water, is called hydrogen 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 3 页，共 10 页chloride, and hydrogen chloride is commonly known as hydrochloric acid. 8, soluble in water alkali are strong alkali, insolubl

16、e in water alkali is weak base From the common strong alkali NaOH, KOH, Ca (OH) 2 and common weak base Fe (OH) 3 and Cu (OH) 2, it seems that the alkali soluble in water is strong alkali, and the alkali which is insoluble in water is weak. In fact, the alkaline strength of alkali and solubility have

17、 nothing to do with, in which soluble in water alkali, dont forget ammonia water, ammonia water is a weak base. Insoluble in water is not necessarily a high base, learn the periodic rate in this section all know, magnesium and hot water after the reaction drops of phenolphthalein red, Mg (OH) 2 is n

18、ot weak, but strong, but Mg (OH) 2 is insoluble. And AgOH, look, Ags metal is so weak that AgOH must be a very weak base. In fact, by measuring the pH value of AgNO3 solution near neutral, we can also know that AgOH is also a strong base. 9, write ion equation, strong electrolyte must be removed, th

19、e weak solution quality must not be dismantled In aqueous solution, it is true that the strong electrolyte is completely ionized in water, so it must be removed; and the weak electrolyte cannot be completely ionized, and therefore does not disassemble. But in non-aqueous solutions, or when the water

20、 in the reaction system is scarce, it depends. In solid phase reactions, either strong electrolyte or weak electrolyte, no matter whether the reaction is realized by ion exchange or not, it can not be removed. Such as: 2NH4Cl+Ca (OH) 2= 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 4 页，共 10 页=CaCl2

21、+2NH3 = +2H2O, this equation will all be removed, therefore cannot be written as the ion equation. Some equations to see a substantive response, such as concentrated H2SO4 and Cu reaction, while the concentration of H2SO4 is 98%, there is a small amount of water, some molecules can also be completel

22、y ionized into H+ and SO42-, but the reaction by using strong oxidation of concentrated H2SO4, reflects the strong oxidation of H2SO4 molecules it is essentially in reaction of the H2SO4 molecule, so the reaction can not be removed in H2SO4. Similarly, the resulting CuSO4 is rare because of water an

23、d is mainly present in molecular form, so it can not be removed. When the weak solution is dissolved, the weak electrolyte is only weak relative to the water, and in some other solvents, it may become a strong electrolyte. For example, CH3COOH is a weak electrolyte in water, but strong electrolyte i

24、n liquid ammonia. When the liquid ammonia is used as a solvent, the CH3COOH takes part in the ion reaction and the CH3COOH can be removed. 10, plastic head dropper must be higher than the test tube mouth This view is incomplete, in some particular conditions, such as the need to avoid excessive air

25、impurities in the experiment, There is no need to make the head dropper higher than the test tube mouth. This example appeared in high school experiments, namely, Fe (OH) 2 production experiments, in order to see the clear white floc, often the plastic head dropper depth into the liquid level 11, ni

26、trate ion must show oxidation 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 5 页，共 10 页In fact, NO3- showed oxidation only in acidic conditions, whereas in alkaline conditions, oxidation was not indicated For example, when asked whether NO3- can coexist with sulfur ions, the answer is yes 12, white

27、and red phosphorus are not soluble in water, and dissolved in CS2? In fact, due to the complex structure of red phosphorus and lead in many aspects (especially physical properties) and display different such as white phosphorus, dissolved in organic solvents, in terms of toxicity, etc. in the custod

28、y of the red phosphorus was not soluble in CS2. 13, the exothermic reaction must be carried out at low temperature, endothermic reaction must be heated A suitable temperature depends on many factors, the first is the price is second, third is the catalytic efficiency, operation difficulty, fourth is

29、 the endothermic and exothermic reactions. Among them, the more important is the price and the catalytic efficiency, and whether or not the object of exothermic is often not considered. In high school, the most prominent example of this is the extraction of ammonia. The reaction between N2 and O2 is

30、 an exothermic reaction, but because of the activity of the catalyst, 500 degrees are chosen as the production temperature. 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 6 页，共 10 页14, must be stronger acid (alkali) can make weak acid (alkali) This is not the case when the temperature and pressure c

31、hange, for example, the production of strong volatile acids is often the use of volatile acids rather than the strength of acids If under normal temperature and pressure, it is not necessarily the case. In the reaction, if precipitation or other phenomena, often affect the law. For example, one of t

32、he most notable examples in each other by alkali, Ca (OH) 2 by NaOH. 15. Must be strong metal, you can replace the metal weak? This rule is often established if the solution is equal to the normal temperature, but the law does not apply if the state of the metal has changed. The most obvious example

33、 is the production of the strongest metal cesium, Cs, which is replaced by Mg from CsCl under the protection of rare gases. 16, all the hydrolysis precipitation is not too big difference The precipitation are hydrolyzed to produce the corresponding pH value range limit, the hydrolysis of Fe3+ can st

34、ably exist in pH=45, Fe2+ and Cu2+ are not. It also explains why the Fe3+ solution will appear obvious precipitation (in fact, this is a misunderstanding, is insoluble in solution is precipitation. But a lot of time, and the hydrolysis of Fe2+ sol) and Cu2+ are generally slightly reaching neutral co

35、nditions was significant. 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 7 页，共 10 页17 in the reaction of Si, Al and NaOH solutions, NaOH is an oxidant In fact, in this reaction, the water of two molecules is omitted, and the hydrogen produced is derived from water, not NaOH, so NaOH is only an alkal

36、ine environment. This knowledge can continue to expand to the elements of the third period and NaOH reaction. So we must consider again, (the oxidant or reductant in the end is what I havent identified, please complete it.), followed by Na, Mg, Al, Si, P, S, Cl. 18, as long as there is a pale yellow

37、 precipitate is AgBr, as long as there is a red precipitate of Fe (OH) 3, as long as there is a green substance in the presence of Fe2+ ions, as long as there is a purple solution must be Potassium Permanganate. and so on.? A yellow precipitate may be S/Ag3PO4/ gold (as in aqua regia displace) /TNT,

38、 and red precipitate may be Cu2O/ copper /HgO, green material may be (that is, Pseudomonas aerugo) Purple solution may be CCl4 solution of iodine. 19, the production of CO2 in the material must contain the existence of CO3 root ions, there is Pb ion must be NO3- salt? Because you tend to ignore orga

39、nic matter, such as oxalic acid and acetic acid, in what seems to be an inorganic reaction, and 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 8 页，共 10 页these organic substances often exhibit properties similar to those of inorganic substances We always ignore the path of organic and inorganic conne

40、ction, in addition to the organic acids just now, as well as the reaction of calcium carbide to acetylene, the reaction of inorganic acids to esters is always neglected. 20, Li sealed with kerosene liquid, liquid Br preservation must be dry, anhydrous? The density of Li is smaller than that of keros

41、ene, so Li is kept under paraffin seal But the fact is often preserved bromine water sealed in the above, the purpose is to prevent the volatilization of bromine. 21, at room temperature, pure phosphoric acid and SO3 are liquid At room temperature, pure phosphoric acid and SO3 are crystalline forms.

42、 Not all acids are either liquid or gaseous, and pure, pure acids are very often seen 22, drainage method = drainage method, exhaust method = exhaust air method? The first one is not going to make any mistakes, and we often see the first such embodiment, such as the row of saturated salt water and t

43、he organic solvent extraction. The key is second, we are not familiar with this, for example, 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 9 页，共 10 页is a collection of NO (NO=28 close to 29). Many students think that NO cannot exhaust was collected, in fact, in the preparation of dry NO ten row CO2 gas is often used, simple and effective. 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 10 页，共 10 页