2022年高中化学个易错知识点.docx

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1、精品_精品资料_【化学】高中化学22 个易错学问点（ chemical high school chemistry 22 fallible points）1, hydroxyl is hydroxylIt 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, orstrongorweak can

2、 ionizeout.So, isnotequaltothehydroxyl hydroxyl.For example,the OH in C2H5OHis hydroxyland willnot ionize; two OHinsulfuricacidarealsohydroxylgroups.As weallknow, sulfuric acid can not ionize OH-. In NaOH, Mg OH 2, Fe OH3, Cu2 OH 2CO3 in OH is the ion, ionization can come out, so here called hydroxy

3、l.2, Fe3+ ion is yellowAs we all know, FeCl3 solution is yellow, but does not meanthat 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. Therefore,the concentrated FeCl3 soluti

4、on is reddish brown, and the average concentration is yellow, which in the final analysisis 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 decomposition可编辑资料 - - - 欢迎下载精品_精品资料_

5、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 andcan be decomposedatroom temperature,so theAgOHisdecomposed immediately after metathesis, so that AgOH does not exist a

6、troom temperature. Water has nothing to do with it. If thisoperation is performed at low temperatures, the white precipitate of AgOH can be obtained.4,polybasicoxygen acid,specificisa few yuan acid,see acid in the number of H.What can the number of H+ polybasic ionization, is to see its structure in

7、 the number of hydroxyl groups, the hydroxyl hydrogen is not non ionizing out. Such as phosphite H3PO3,itlooksliketherearethreeH, itseemstobe threeyuan acid, but its structure is that there is a H and a O, respectively,and thecentralatoms aredirectlylinked,butnota hydroxyl. There are only two O and

8、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 acidic solution.Onthesurface,theacidsaltsolutionisacidic,butitisnot.In the end what is salt, to discuss the sit

9、uation, when the ionization degree is greater than the degree of hydrolysis, acidic, when the degree of ionization is less than the degreeofhydrolysis,alkaline.Ifthisisa strongacidsalt,because it produce a large number of H+, and anion hydrolysis, so the可编辑资料 - - - 欢迎下载精品_精品资料_acidic acid acid salt

10、solution. But the weak acid salt, then compare it to produce the H+ capacity and the degree of hydrolysis of the anion. If the degree of hydrolysis of theanion is greater e.g., NaHCO3, NaHS, Na2HPO4, the solution is alkaline; conversely, if the anion has a stronger abilityto ionize H+ e.g., NaH2PO4,

11、 NaHSO3, the solution is acidic.6 and H2SO4 have strong oxidizing propertyThats not right. Just add a thick word in the front. Thats right. Concentrated H2SO4exists in the form of molecules, its oxidation is reflected in the overall molecules, the H2SO4 inS is +6 valence, easy to get electrons, so i

12、t has strong oxidation.The oxidationofdiluteH2SO4orSO42- isalmostno evenH2S is not oxidized, much less oxidized than that of H2SO3 orSO32-.Italsoshows thattheoxidationofthenonmetallicoxo radical is stronger than that of the high valence state, andtheacidityofHClOissimilartothatofHClO4. Therefore,whe

13、n H2SO4 has strong oxidation, it must be rigorous, with thickin front.7 hydrochloric acid is commonly known as hydrogen chlorideItseemsthatbothofthem have thesamechemicalformula,which may lead to misunderstandings. Hydrochloric acid is commonlyknown as hydrogen chloride. In fact, hydrochloric acid i

14、s amixture,a mixtureofhydrogen chlorideand water;and hydrogen chlorideisa pure substance,whichisfundamentallydifferent.Hydrogen chloride, dissolved in water, is called hydrogen可编辑资料 - - - 欢迎下载精品_精品资料_chloride, and hydrogen chloride is commonly known as hydrochloric acid.8,solubleinwateralkaliare str

15、ongalkali,insolubleinwater alkali is weak baseFrom the common strong alkali NaOH, KOH, Ca OH 2 and common weak base Fe OH 3 and Cu OH 2, it seems that the alkalisoluble in water is strong alkali, and the alkali which isinsoluble in water is weak. In fact, the alkaline strength ofalkaliand solubility

16、have nothingtodo with,inwhich soluble in water alkali, dont forget ammonia water, ammonia water isa weak base. Insoluble in water is not necessarily a high base, learn the periodic rate in this section all know, magnesiumand hot water after the reaction drops of phenolphthalein red, MgOH 2 isnotweak

17、,butstrong,butMgOH 2 isinsoluble.And AgOH, look,Agsmetalisso weak thatAgOHmust be a veryweak base.Infact,by measuringthepH valueofAgNO3solutionnear neutral, we can also know that AgOH is also a strong base.9,writeionequation,strongelectrolytemust be removed,the weak solution quality must not be dism

18、antledInaqueous solution,itistruethatthestrongelectrolyteis completelyionizedinwater,so itmust be removed; and theweak electrolyte cannot be completely ionized, and therefore doesnot disassemble. But in non-aqueous solutions, or when the water in the reaction system is scarce, it depends. In solidph

19、ase reactions,eitherstrongelectrolyteorweak electrolyte,no matter whether the reaction is realized by ion exchange or not, it can not be removed. Such as: 2NH4Cl+Ca OH 2=可编辑资料 - - - 欢迎下载精品_精品资料_=CaCl2+2NH3 = +2H2O, this equation will all be removed,thereforecannotbe writtenas theionequation.Someequa

20、tions to see a substantive response, such as concentrated H2SO4 andCu reaction,whiletheconcentrationofH2SO4is98%, thereisa smallamount ofwater,some moleculescan alsobe completely ionized into H+ and SO42-, but the reaction by using strongoxidationofconcentratedH2SO4,reflectsthestrongoxidation of H2S

21、O4 molecules it is essentially in reaction of the H2SO4 molecule,so the reactioncan notbe removed inH2SO4.Similarly, the resulting CuSO4 is rare because of water and is mainlypresent in molecular form, so it can not be removed. When the weak solution is dissolved, the weak electrolyte is only weakre

22、lativetothewater,and insomeothersolvents,itmaybecome a strong electrolyte. For example, CH3COOH is a weakelectrolyteinwater,butstrongelectrolyteinliquidammonia. Whentheliquidammoniaisused as a solvent,theCH3COOtHakes part in the ion reaction and the CH3COOH can be removed.10,plastichead droppermust

23、be higherthanthetesttubemouthThis view is incomplete, in some particular conditions, suchas theneed toavoidexcessiveairimpuritiesinthe experiment,There is no need to make the head dropper higher than the test tube mouth.This example appeared in high school experiments, namely, FeOH 2 productionexper

24、iments,inordertosee theclearwhite floc,oftenthe plastichead dropperdepthintotheliquidlevel11, nitrate ion must show oxidation可编辑资料 - - - 欢迎下载精品_精品资料_In fact, NO3- showed oxidation only in acidic conditions, whereas in alkaline conditions, oxidation was not indicatedFor example, when asked whether NO

25、3- can coexist with sulfur ions, the answer is yes12, white and red phosphorus are not soluble in water, and dissolved in CS2.Infact,due tothecomplex structureofredphosphorus and lead in many aspects especially physical properties and displaydifferent such as white phosphorus, dissolved in organicso

26、lvents, interms oftoxicity, etc. inthe custodyof the red phosphorus was not soluble in CS2.13, the exothermic reaction must be carried out at low temperature, endothermic reaction must be heatedA suitable temperature depends on many factors, the first is the price is second, third is the catalytic e

27、fficiency,operation difficulty, fourth is the endothermic and exothermic reactions. Amongthem, the more important is the price and the catalytic efficiency, and whether or not the object ofexothermic is often not considered.In high school, the most prominent example of this is the extraction of ammo

28、nia. The reaction between N2 and O2 is an exothermic reaction, but because of the activity of thecatalyst,500 degrees are chosen as the productiontemperature.可编辑资料 - - - 欢迎下载精品_精品资料_14,must be strongeracidalkalican makeweak acidalkaliThisisnotthecase when thetemperatureand pressure change, for examp

29、le, the production of strong volatile acids is oftenthe use of volatile acids rather than the strength of acidsIfundernormal temperatureand pressure,itisnotnecessarily thecase.Inthereaction,ifprecipitationorotherphenomena, often affect the law. For example, one of the most notableexamples in each ot

30、her by alkali, Ca OH 2 by NaOH.15. Must be strong metal, you can replace the metal weak.Thisruleisoften establishedifthesolution is equalto the normal temperature,butthe law doesnotapplyif the stateof the metal has changed.The most obvious example is the production of the strongest metal cesium, Cs,

31、 which is replaced by Mg from CsCl under the protection of rare gases.16,allthehydrolysisprecipitationisnottoobigdifferenceThe precipitationare hydrolyzed toproducethe corresponding pH value range limit, the hydrolysis of Fe3+ can stably existinpH=45, Fe2+ and Cu2+arenot.Italsoexplainswhy theFe3+sol

32、ution will appear obvious precipitation in fact, this isa misunderstanding,isinsolubleinsolutionisprecipitation. Buta lotoftime,and thehydrolysisofFe2+ soland Cu2+ are generally slightly reaching neutral conditions wassignificant.可编辑资料 - - - 欢迎下载精品_精品资料_17 in the reaction of Si, Al and NaOH solution

33、s, NaOH is an oxidantInfact,inthisreaction,thewateroftwo moleculesisomitted, and the hydrogen produced is derived from water, not NaOH, soNaOH is only an alkaline environment.This knowledge can continue to expand to the elements of thethirdperiodand NaOHreaction.So we must consideragain,the oxidant

34、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 precipitate is AgBr, aslongas thereisa red precipitateofFe OH 3,as longas there is a green substance in the presence of Fe2+ ions, as long asthere is a

35、purple solution must be Potassium Permanganate.and so on.A yellow precipitate may be S/Ag3PO4/ gold as in aqua regia displace /TNT, 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

36、 in the material must contain the existence of CO3 root ions, there is Pb ion must be NO3- salt.Because you tendtoignoreorganicmatter,such as oxalicacid and aceticacid,inwhat seemstobe an inorganicreaction,and可编辑资料 - - - 欢迎下载精品_精品资料_these organic substances often exhibit properties similar to those

37、of inorganic substancesWealwaysignorethepathoforganicand inorganicconnection, in addition to the organic acids just now, as well as thereaction of calcium carbide to acetylene, the reaction ofinorganic acids to esters is always neglected.20,Lisealedwithkerosene liquid,liquidBr preservationmust be dr

38、y, anhydrous.The density of Li is smaller than that of kerosene, so Li is kept under paraffin sealBut the fact is often preserved bromine water sealed in theabove,thepurposeistopreventthevolatilizationofbromine. 21,atroom temperature,pure phosphoricacidand SO3are liquidAt room temperature, pure phos

39、phoric acid and SO3 arecrystallineforms.Not allacidsareeitherliquidorgaseous, and pure, pure acids are very often seen22,drainagemethod = drainagemethod, exhaustmethod = exhaust air method.The first one is not going to make any mistakes, and we oftensee thefirstsuch embodiment, such as therow ofsatu

40、ratedsalt water and the organic solvent extraction.The key is second, weare not familiarwith this, forexample,可编辑资料 - - - 欢迎下载精品_精品资料_isa collectionof NO NO=28 closeto29.Many studentsthink that NO cannot exhaust was collected, in fact, in thepreparationofdryNOtenrow CO2gas isoftenused,simpleand effective.可编辑资料 - - - 欢迎下载