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1、离子方程式的书写归纳（Writing induction of ionic equation）The writing of ionic equation.Txt the most precious thing in the world is not what you can never get or what you get, but what you have gained and may lose at any moment! Love is a lamp, while friendship is the shadow. When the lamp is off, you will fin
2、d the shadow everywhere. Friend is who can give you strength at last.Writing induction of ionic equationSun Xiumin, middle Heilongjiang, QinganIon equation and ion coexistence has been a hot topic in the college entrance examination. It can be said that it is often new and lasting. For writing or th
3、e true or false ion equation, some of the students is not a test, often wrong. In fact, such problems are not difficult, as long as the master of various types of ion reaction equation writing method, careful analysis, you can accurately answer, are summarized as follows:First, the reagent dosage is
4、 different, the ionic equation is differentAbout 1. of the amount of acid salt and ion equation writingIn general, the number of ions is determined according to the chemical formula of an inadequate amount of substance, and the ion equation of the reaction is written. The ratio of the amount of subs
5、tance involved in the amount of ions in the reaction is not necessarily consistent with the chemical formula. If there is no definite dosage, it is correct to use any reactant as an adequate ion equation.Example 1. Write out the corresponding ionic equation:(1) a sufficient amount of NaHSO4 solution
6、 is mixed with Ba (HCO3) 2 solution(2) a sufficient amount of Ba (HCO3) 2 solution mixed with NaHSO4 solution(3) add sufficient amount of NaOH solution to Ca (HCO3) 2 solution(4) add sufficient amount of Ca (HCO3) 2 solution to NaOH solutionResolution: (1) both Ba2+ and HCO3- are involved in the rea
7、ction, and the NaHSO4 is excessive, so Ba2+ and HCO3- appear as 1:2 in the ionic equation, and H+ and SO42- are determined as needed;(2) when the Ba (HCO3) 2 is sufficient, the ionic equation depends on the amount of NaHSO4, and H+ and SO42- can only appear in 1:1, so Ba (HCO3) 2 HCO3- does not reac
8、t completely;(3) Ca2+ and HCO3- appear as 1:2;(4) according to the quantity of Ca (HCO3) 2 matter more than NaOH, then HCO3- and Ca2+ can only appear in 1:1.Answer: (1) 2H+SO42-+Ba2+2HCO3-=BaSO4: +2CO2 = +2H2O(2) H+SO42-+Ba2+HCO3-=BaSO4: +CO2 = +H2OCa2+2HCO3-+2OH-=CaCO3 (3): +2H2O+CO32-Ca2+HCO3-+OH-
9、=CaCO3 (4): +H2O2. the writing of an ionic equation in which the product of the product can react with an excess substanceSuch reactions only need to indicate the conditions given by the subject and determine whether the product continues to react with excess substance, and as long as the product is
10、 determined correctly, the corresponding ionic equation can be written out.Example 2. Write the ionic equation for the following reactions:(1) the reaction of NaOH solution with sufficient AlCl3 solution;(2) the reaction of AlCl3 solution with sufficient NaOH solution;Analysis: NaOH and AlCl3 reacti
11、on of Al (OH) 3 is a typical amphoteric hydroxide, it does not dissolve in excess AlCl3 solution, but can be dissolved in excess NaOH solution, generating sodium metaaluminate.Answer: (1) Al3+3OH-=Al (OH) 3 (2): Al3+4OH-=AlO2-+2H2OExample 3. Write the ionic equation for the following reactions:(1) a
12、 small amount of CO2 was injected into the NaAlO2 solution(2) adequate amount of CO2 was injected into the NaAlO2 solution(3) adding excessive amounts of HCl to NaAlO2 solution;Resolution: Al (OH) 3 is only soluble in strong acid or strong alkali solution, so when CO2 is excessive, it will not disso
13、lve; but CO32- can react with excess CO2 to form HCO3-. When HCl is excessive, Al (OH) 3 continues to react with H+ to produce Al3+ and H2O.Answer: (1) 2AlO2-+CO2+3H2O=2Al (OH) 3: +CO32-(2) AlO2-+CO2+2H2O=Al (OH) 3: +HCO3-(3) AlO2-+4H+=Al3+2H2OThreeThe writing of a more specific ionic equationIn add
14、ition to considering the relationship between the amount of the reaction, other special factors should be considered, such as the solubility of the product and the ratio of ions, so that the ion equation can be correctly written out.Example 4. Write the ionic equation for the following reactions:(1)
15、 Mg (HCO3) 2 solution reacts with excess NaOH solution(2) reaction of alum solution with sufficient amount of Ba (OH) 2 solution;(3) a sufficient amount of barium hydroxide solution was added into ammonium hydrogen sulfate solution(4) to the new water drops in a small amount of ferrous bromide solut
16、ionAnalysis: (1) because Mg (OH) 2 is more insoluble than MgCO3, Mg2+ does not react with CO32- to form MgCO3, but reacts directly with OH- to form Mg (OH) 2.(2) the ratio of the amount of Al3+ and SO42- in the alum solution is 1:2, not 2:3, and the Al (OH) 3 can not be neglected, that is, Al3+ is c
17、onverted into AlO2 after reaction.(3) three kinds of ions ionized into NH4HSO4 are involved in the reaction, the reaction can not ignore the generation of weak electrolyte NH3 and H2O, while the NH4HSO4 excess occurs: Ba2+2OH-+2H+SO42-=BaSO4: +2H2O reaction.(4) for this reaction, we should pay atten
18、tion not only to the ratio of the amount of substance Fe2+ and Br- to 1:2, but also to the reaction of Fe2+ and Cl2.Answer: (1) Mg2+2HCO3-+4OH-=Mg (OH) 2: +2CO32-+2H2OAl3+2SO42-+2Ba2+4OH-=AlO2-+2BaSO4 (2): +2H2O(3) NH4+H+SO42-+Ba2+2OH-=NH3 - H2O+BaSO4: +H2O(4) 2Fe2+4Br-+3Cl2=2Fe3+2Br2+6Cl-Two, addin
19、g reagents in different order, ionic equation is differentThe different order of reagents will lead to the excess or deficiency of some substances, and then different ion reactions will occur.In example 5, (1) gradually pour NaOH solution to excess in AlCl3 solution(2) gradually pour AlCl3 solution
20、into the NaOH solution to excess. Write out the ionic equations for the reactions in these two processesResolution: (1) AlCl3, Al (OH) 3, NaAlO2 (2), NaOH, NaAlO2, Al (OH) 3Answer: (1) +3OH-=Al (OH) 3: Al (OH) 3+OH-=AlO2-+2H2OTotal response: Al3+4OH-=AlO2-+2H2O(2) +4OH-=AlO2-+2H2O 3AlO2-+Al3+6H2O=4A
21、l (OH): 3The total reaction type: Al3+3OH-=Al (OH): 3Example 6. Write the ionic equation for the following reactions:(1) add a few drops of dilute hydrochloric acid to the Na2CO3 solution(2) add a few drops of Na2CO3 solution to dilute hydrochloric acidAnalysis: (1) Na2CO3 excess, the chemical equat
22、ion is: Na2CO3+HCl=NaHCO3+NaCl(2) hydrochloric acid overdose chemical equation: Na2CO3+2HCl=2NaCl+H2O+CO2 =Answer: (1) - (2) CO32-+2H+=H2O+CO2 = CO32-+H+=HCO3Three, reagent conditions or reaction conditions are different, ionic equation is differentThe same material may be different because of the e
23、xistence of the form or the environment, and the reactions of ions may be influenced by the temperature of some substances.Example 7, (1) lime milk mixed with NH4HCO3 concentrated solution(2) dilute Ca (OH) 2 solution mixed with dilute NH4HCO3 solutionAnalysis: (1) lime milk should be written in ion
24、ic formula as a molecular form, the concentration of NH3 and H2O is large, and it should be decomposed and released NH3 when heated.(2) the form of existence of Ca (OH) 2 and NH3 H2O is the opposite of (1).Answer: (1) Ca (OH) 2+NH4+HCO3-= CaCO3: +NH3 = +2H2OCa2+2OH-+NH4+HCO3-=CaCO3 +NH3 (2): H2O+H2O
25、In 8 cases, KOH was added to the water, try to write without heating and heating (KClO3) two case reaction ion equation.Analysis: the chemical equation for the reaction is: (1) 2KOH+Cl2=KCl+KClO+H2O(2) 6KOH+3Cl2 5KCl+KClO3+3H2OAnswer: (1) 2OH-+Cl2=Cl-+ClO-+H2O (2) 6OH-+3Cl2 5Cl-+ClO3-+3H2OFour, reag
26、ent concentration is different, ionic equation is differentThe reaction of reagents with different concentrations may result in different ionic equations because of the different kinds of the products, and even the non-ionic reactions, such as concentrated H2SO4 and zinc reactions, do not belong to
27、the ionic reaction. The concentration may be different, the product type is the same, but the product state is different, ionic equation is not the same.Example 9. Write the ionic equation for the reaction of copper with concentrated nitric acid and dilute nitric acid.analysis the reaction of concen
28、trated nitric acid with copper is reduced to NO2 and reduced to NO if dilute nitric acid.Answer: (1) Cu+4H+2NO3-=Cu2+2NO2 = +2H2O(2) 3Cu+8H+2NO3-=3Cu2+2NO = +4H2OExample 10. Write the ionic equation of excess CO2 into dilute Na2CO3 solution and saturated Na2CO3 solution.Analysis: Na2CO3, CO2, H2O re
29、action NaHCO3, NaHCO3 completely dissolved in dilute solution, but the saturated Na2CO3 solution Na2CO3 more, formed when CO2 NaHCO3 is too much, but the solubility of NaHCO3 little, most NaHCO3 in solid form.Answer: CO32-+CO2+H2O=2HCO3-: 2Na+CO32-+CO2+H2O=2NaHCO3Five, special ionic equationSome ion
30、ic equations are different from conventional ones because of the special nature of the reactants.Example 11. Use ionic equation to describe the following process or result:(1) sodium alcohol solution was alkaline(2) heating and filtration can remove Fe3+ in KNO3 solution(3) the Na2SO3 solution is ex
31、posed to the air, resulting in a decrease in pH(4) SO2 passes into NaClO solutionAnalysis: due to ethanol than water to ionization, so CH3CH2O- can combine water ionization of the H+, the solution of C (OH-) c (H+); Fe3+ must be filtered to remove Fe3+ into precipitation, the anions in the solution
32、only NO3- and water ionization of the OH-, the Fe3+ is hydrolyzed to Fe (OH) 3; SO32- hydrolysis is alkaline, while pH decreased because of exposed in the air oxidation of SO32- into SO42-, SO42- was not so pH value decreases. SO2 has stronger reducibility, and NaClO solution has oxidation, so they do not happen the complex decomposition reaction of strong acid and weak acid, but produce oxidation reduction reaction, produce Cl- and SO42-.Answer: (1) CH3CH2O-+H2OCH3CH2OH+OH- (2) Fe3+3H2OFe (OH) 3: +3H+(3) SO32-+H2O HSO3-+OH-2SO32-+O2=2SO42- (4) ClO-+SO2+H2O=Cl-+SO42-+2H+