Ionic reactions and ionic equations.
Prerequisite Knowledge Requirements].
1.Understand the concept of electrolytes and understand the concepts of strong and weak electrolytes.
2.Understand the ionization of electrolytes in water and the conductivity of electrolyte solutions.
3.Understand the concept of ionic reactions and the conditions under which ionic reactions occur.
4.Able to write ion equations correctly and perform relevant calculations.
Key Competencies and College Entrance Examination Requirements].
Key competency requirements: microscopic imagination ability, comprehension and analysis ability.
College Entrance Examination Requirements: The content of this section is a hot topic of high-frequency propositions, which tests three abilities.
One. To test the writing ability of ion equations, the test questions are mainly fill-in-the-blank, and may appear in process flow questions and experimental comprehensive questions. Use the information in the question to write unfamiliar ion equations and learn how to balance unfamiliar ion equations.
2. The ability to judge the truth and error of the ion equation is tested in the multiple-choice questions.
3. The ability to judge whether ions can coexist. Tested in multiple-choice questions.
Analysis of Discipline Core Literacy].
Macroscopic identification and microscopic analysis: can understand the similarities and differences between chemical reactions and ionic reactions from different levels;Able to understand the law of ion conduction in solution from a microscopic perspective, understand chemical reactions and ionic reactions from a combination of macroscopic and microscopic perspectives, and use ionic reactions to solve practical problems.
Evidence Reasoning and Model Cognition: Have evidence awareness, be able to analyze and reason based on the difference in the conductivity of different electrolyte solutions, and understand the ionization characteristics and conductivity laws of electrolytes in solutionsUnderstand the essential characteristics of the research object through analysis, reasoning and other methods;Be able to use the correct model to understand how to write ion equations.
Essential knowledge point 1: Electrolytes and ionization.
1. Electrolytes and their classification.
1.Comparison of electrolytes versus non-electrolytes.
2.Conductivity of electrolytes.
1) Comparison of the causes of metal conduction and electrolyte solution.
Metal conductivity is due to the directional movement of free electrons under the action of electric field, high temperature, large amplitude of metal cation vibration, increased resistance to free electron directional movement, and weakened metal conductivity.
The electrolyte solution conducts electricity due to the presence of freely moving ions in the solution. When the temperature increases, the ionization degree of the weak electrolyte increases, the ion concentration increases, and the conductivity increases.
2) The conductivity of the electrolyte solution is determined by the concentration of freely moving ions in the solution and the charge number of the ions, which is not necessarily related to the strength of the electrolyte.
3.Strong electrolytes and weak electrolytes.
1) Strong electrolyte: An electrolyte that can be fully ionized in solution. then there is no ionization equilibrium in the strong electrolyte solution.
2) Weak electrolyte: An electrolyte that is only partially ionized in solution. then there is ionization equilibrium in the weak electrolyte solution.
3) Comparison of strong and weak electrolytes:
2. Ionization of electrolytes.
1.Ionization. Concept: The process by which an electrolyte is dissociated into freely moving ions in an aqueous solution or in a molten state.
Ionization conditions: The ionization conditions for acids are soluble in water, and the ionization conditions for salts and bases are soluble in water or melted.
2.Writing of ionization equations.
1) Strong electrolytes.
Completely ionized, denoted by "===". For example, the ionization equation for H2S4O is: H2SO4===H SO42-.
2) Weak electrolytes.
Partially ionized, denoted by " ". For example, the ionization equation for HClL is: Hclo H ClO.
The multiple weak acids are ionized step by step, and the degree of ionization is gradually weakened, and the first step ionization is the main one. For example, the ionization equation for h3po4 is.
h2po4≒h＋＋h2po4-；h2po4-≒h＋＋hpo42-；hpo24-≒h＋＋po43-
The multivariate weak base ionizes step by step, but writes out in one step.
For example, the ionization equation of Cu(OH)2 is: Cu(OH)2 Cu2 2OH.
Amphoteric hydroxides are ionized in both directions.
For example, the ionization equation of Al(OH)3: Halo2- H2O Al(OH)3 Al3 3OH.
3) Acid salts.
Strong acidic acid salts are completely ionized and written in one step.
For example, the ionization equation of NaHSO4 in aqueous solution is: NaHSO4===Na HSO42-, and the ionization equation in the molten state is: NaHSO4===Na HSO4-.
In the first step of the polyliquity of weak acid acid salts, the first step is completely ionized, and the rest is ionized. For example, the ionization equation of NaHSO3 in aqueous solution is: NaHSO3===Na HSO3-, HCO3- HSO32-.
Knowledge comprehension points].
1.Elemental and mixtures are neither electrolytes nor non-electrolytes, such as Cu, NaCl solutions. Electrolytes and electrolyte solutions are different, such as HCl and hydrochloric acid, which is neither an electrolyte nor a non-electrolyte.
2.Electrolytes do not necessarily conduct electricity, such as solid NaCl, liquid HCl, etc.;At room temperature, most electrolytes do not conduct electricity on their own. Substances that can conduct electricity are not necessarily electrolytes, such as metallic elements such as iron and aluminum.
3.Electrolytes are compounds that conduct electricity by ionization, such as CO2, SO2, SO3, and NH3 in aqueous solutions, which can conduct electricity, but are all non-electrolytes.
4.The strength of the electrolyte is not directly related to the conductivity of the electrolyte solution and the size of the solubility, such as calcium carbonate, which has small solubility and poor conductivity of the solution, but it belongs to a strong electrolyte.
5.The conductivity of the strong electrolyte solution is not necessarily strong, and the conductivity of the weak electrolyte solution is not necessarily weak, for example, the conductivity of the extremely dilute NaCl solution is not as strong as that of concentrated ammonia. The conductivity of the solution depends on the size of the ion concentration and the amount of charge carried by the ion, the greater the ion concentration and the more the number of charges carried by the ion, the stronger the conductivity.
6.According to the periodic table, break through the memory of strong and weak electrolytes.
A: Except for Lioh, the rest are strong bases.
A: Except for mg(oh)2 and be(oh)2, the rest are strong bases.
A: Al(OH)3 is an amphoteric hydroxide.
A: H2CO3 and H2SiO3 are weak acids.
A: strong acid: Hno3;Moderately strong (or weak) acids: HNO2, H3PO4.
A: strong acid: H2SO4;Weak acids: H2SO3, H2S.
A: Strong acids: HCl, HBR, Hi, HCO4, etc.;Weak acids: HF, HCl, etc.
Common weak bases in transition elements: Fe(Oh)3, Fe(Oh)2, Cu(Oh)2, etc.
Confusion point analysis] to judge the right and wrong (the correct hit" "the wrong hit" "
1.H2SO4 is a strong electrolyte, and concentrated sulfuric acid has strong electrical conductivity. (
2.The Kno3 solution is ionized into K+ and N under the action of electric current. (
3.CaCO3 and AGCL are insoluble in water and are non-electrolytes. (
4.Chlorine gas does not conduct electricity, and chlorine water conducts electricity because the electrolyte formed by the reaction of chlorine gas with water is ionized and conducted, so chlorine gas is a non-electrolyte. (
5.A solution with a large concentration must have a stronger conductivity than a solution with a small concentration. (
6.Na2O is dissolved in water and reacts with water to form NaOH, and NaOH ionizes ions, so NaOH is an electrolyte, while Na2O is a non-electrolyte. (
Benchmarking case analysis and tracking drill].
Basic case analysis] Correct and false judgment of electrolyte and its ionization.
Example 1 The statement about electrolytes is wrong.
A The substance that can be ionized is the electrolyte b The strong electrolyte is completely ionized in an aqueous solution.
c The substance that conducts electricity is not necessarily an electrolyte d Water is an extremely weak electrolyte.
Follow-up drill] 1The following groups are categorized as strong electrolytes, weak electrolytes, and non-electrolytes, and the correct one is ( ).
2.The following statement is correct ( ).
A NaHCO3 is a strong electrolyte, so the ionization equation of NaHCO3 is NaHCO3===Na HCO
b At room temperature, 0If the pH 11 of a BoH solution of 1 mol·l 1 is the ionization equation of BoH OH
The pH of the C 25 NaA solution is >7, then the ionization equation for HA is HA===HA
The conductivity of the saturated aqueous solution of d CaCO3 is very weak, so the ionization equation of CaCO3 is CaCO3Ca2 Co
3.Of the following statements, the correct one is.
a Strong electrolyte must be more conductive than a weak electrolyte.
b The conductivity of a substance with low solubility must be weaker than that of a substance with a high solubility.
c Pure water has poor electrical conductivity, but water is also an electrolyte.
d The electrolyte must be able to conduct electricity.
Puzzle point analysis] Answer] 1× 2.× 3.× 4.× 5.× 6.×
Benchmarking case analysis and tracking drill].
Basic case analysis] Correct and false judgment of electrolyte and its ionization.
Example 1 Answer] a
Analysis] item a: The electrolyte is a compound that moves freely in an aqueous solution or in a molten state, and the substance that can be ionized is not necessarily in an aqueous solution or in a molten state, so it is not necessarily an electrolyte, and item A is wrong;
Item B: Strong electrolytes can be completely ionized in aqueous solution, item B is correct;
Item C: The electrolyte is a compound, and a part of the metal element is a conductor that can conduct electricity, but it is not a compound, so the substance that can conduct electricity is not necessarily an electrolyte, and item C is correct;
D term: Water is a weak electrolyte that can undergo weak ionization, and D term is correct;The answer is A.
Follow-up drill] 1【Answer】c.
Analysis] item a: Fe in is neither an electrolyte nor a non-electrolyte, false;
Item B: NH3 is a non-electrolyte, BaSO4 is a strong electrolyte, false;
Item C: CaCO3 strong electrolyte, H3PO4 weak electrolyte, C2H5OH non-electrolyte, correct;
Item D: H2O is a weak electrolyte, false.
Answer] B Analysis] Item A: HCO3 is not completely ionized, and NaHCO3 ionization should be written step by step;
Item B: BOH is a weak base, reversible ionization;
Item C: HA is a weak acid, reversible ionization;
Item D: CaCO3 is insoluble, but it is a strong electrolyte, and all of it is ionized.
Answer] C Analysis] Item A: The conductivity of a strong electrolyte is not necessarily stronger than that of a weak electrolyte, and the conductivity is related to the concentration of the substance and the number of charges in the ion belt
Item B: There is no necessary relationship between the size of solubility and conductivity, and the dissolved substances may not all be ionized
C: Pure water has a very poor electrical conductivity, but it can be ionized and conducted, so water is an electrolyte, correct, choose C;
Item D: The conduction of electrolytes requires certain conditions: aqueous solution or molten state, such as solid sodium chloride is not conductive, do not choose D.