First, the basic concepts and basic theories
1. The nucleus of an atom is generally made of protons and neutrons; but there are no neutrons in the nucleus of a krypton.
2. The outermost electron number of the atom is less than or equal to 2 is generally a metal atom; but the outermost electron number of the hydrogen and helium atoms is 1 and 2, respectively, and they are not metallic elements.
Particles with the same total number of protons as the total number of extranuclear electrons are generally the same kind of particles; with the exception of Ne and HF.
4. There are generally electrons outside the nucleus of ions; but there are no electrons outside the nucleus of hydrogen ions (H+).
5. Gas elements are generally composed of diatoms; but noble gases are single atoms and ozone is composed of three atoms.
6. Substances composed of the same element are generally elementary and pure; but O2 and O3, white phosphorus and red phosphorus are mixtures.
7. The reaction of two or more substances to produce a substance is generally a chemical synthesis reaction; For example: 3O2=2O3,2NO2
N2O4。
8. The atoms are highly reactive, and the corresponding elemental properties are generally more active; but the nitrogen atoms are active, and the nitrogen gas is very stable.
9. Metal oxides are generally alkaline oxides; but Mn2O7 is an acidic oxide, and Al2O3 and ZnO are amphoteric oxides.
10. Non-metallic oxides are generally acidic oxides; but CO and NO are not acidic oxides.
11. Anhydride is generally a non-metallic oxide; however, the anhydride Mn2O7 of HMnO4 is a metal oxide.
12. Anhydride is generally an oxide; with exceptions such as acetic anhydride [(CH3CO)2O].
13. The oxides soluble in water-forming acids are generally acid anhydrides; but NO2 is soluble in water to form nitric acid, and the nitric acidic anhydride is N2O5.
14. An acid corresponding to an anhydride is generally an acid; but P2O5 is both an anhydride of metaphosphate (HPO3) and anhydride of phosphoric acid (H3PO4).
15. Anaerobic acids are generally hydrides of non-metallic elements; with the exception of hydrocyanic acid (HCN).
16. The "yuan number" of the acid is generally equal to the number of hydrogen atoms in the acid molecule; but the phosphorous acid (H3PO3) is not a ternary acid but a dibasic acid, the hypophosphoric acid (H3PO2) is not a ternary acid but a monobasic acid, and the boric acid (H3BO3) is not a ternary acid but a monobasic acid, etc.
17. In an oxygen-containing acid formed by a non-metallic element, the higher the valence of the element, the stronger the oxidation of the corresponding acid, but the oxidation of hypochlorous acid (HClO) is stronger than that of aerochloric acid (HClO4).
18. Elements with metallic luster and can conduct electricity are generally metals; but non-metallic graphites with metallic luster can also conduct electricity.
19. The saturated solution generally becomes an unsaturated solution after the temperature is raised; however, the saturated solution of Ca(OH)2 is still a saturated solution after the temperature is raised.
The boiling point of the mixture generally has a certain range, rather than at a certain temperature; but the boiling point of 95.5% alcohol solution is fixed at 78.1 °C.
21. The cations generated when the electrolyte is ionized are all hydrogen ions, and the compounds are acids; but the cations produced by hydroion are all hydrogen ions, but the water is neither acidic nor alkaline.
22. Usually the larger the concentration of the solution, the greater the density, but the greater the concentration of ammonia, ethanol and other solutions, the greater the density decreases.
23. When the solvent is evaporated, the mass fraction of the general solution will increase; but when heating hydrochloric acid and ammonia, the mass fraction will decrease.
24. The crystals of the salt can generally be obtained by heating the evaporated salt solution; but the solids obtained by heating the evaporated AlCl3 and FeCl3 solutions are mainly Al2O3 and Fe2O3.
25. Acid salt solutions are generally acidic, but NaHCO3 is hydrolyzed to a large extent and its solution is alkaline.
26. Strong acids are generally made into weak acids, and weak acids generally cannot be made into strong acids; but H2S gas is passed through the solution of CuSO4, and the reaction is: H2S + CuSO4 = CuS + H2SO4.
27. Strongly oxidizing acids (concentrated H2SO4, concentrated HNO3) - generally can oxidize reactive metals; but iron and aluminum are passivated in cold concentrated H2SO4 or concentrated HNO3.
28. Acids generally do not react with acids; but concentrated H2SO4 and H2SO3 can oxidize H2S: H2S + H2SO4 (concentrated) = SO2 + S | ＋2H2O， 2H2S＋H2SO3=3S ＋3H2O。
Bases generally do not react with bases; however, amphoteric Al(OH)3 can react with NaOH, and ammonia can react with Cu(OH)2.
30. Acid oxides generally cannot react with acids; however, the following reactions can occur: SiO2 + 4HF = SiF4↑+ 2H2O, 2H2S + SO2 = 3S + 2H2O.
31. Acids and bases generally neutralize reactions to produce salts and water; with the following exceptions: 3H2S + 2Fe (OH) 3 = 2FeS + S + 6H2O, 3Fe(OH)2 + 10HNO3 = 3Fe(NO3) 3 + NO↑+ 8H2O.
32. According to the list of metal activity order, the metal element in the front can generally replace the metal in the back from its salt; but Na, K, etc. react with water first, and then react with salt.
33. Metal and salt solutions generally undergo displacement reactions; with the following exceptions: 2FeCl3 + Fe→3FeCl2; 2FeCl3 + Cu →2FeCl2 + CuCl2; metal and alkali solutions generally do not react; but AI and Zn react with NaOH solutions.
35. The reaction of salt and salt solution generally produces two new salts; except for the occurrence of double hydrolysis between two salt solutions. If the sodium sulfide solution is added dropwise to the aluminum sulfate solution, the ion equation of the reaction is: 2Al2S3 + 6H2O = 2Al(OH) 3 + 3H2S
Salts and bases generally react to generate new salts and neoallines; with the following exceptions: NaHSO4 + NaOH →Na2SO4 + H2O, NaHCO3 + NaOH = Na2CO3 + H2O, CH3 COONa + NaOH
Na2CO3 ＋ CH4
37. The reaction of salts with acids generally produces new salts and new acids; with the following exceptions: 2KMnO4 + 16HCl = 2KCl + 2MnCl2 + 5Cl2 + 8H2O
38. The aqueous solution of gaseous hydrides of non-metallic elements of VA, VIA, and VIA is generally acidic; however, H2O is neutral and the aqueous solution of NH3 is weakly alkaline.
39. Each cycle in the periodic table generally begins with metallic elements;
The greater the number of electron layers in an atom, the greater the atomic radius, with the exceptions of Li>Al> Mg>Ca, Ra> Ba, etc.
41. With the increase of atomic number, the relative atomic mass of the elements generally increases gradually; however, the relative atomic mass of argon is greater than that of potassium, and tellurium is greater than that of iodine.
42. Ionic crystals generally contain metallic elements; but NH4Cl, NH4NO3 and other metal-free elements.
43. The melting point of ionic crystals is generally lower than that of atomic crystals; however, the melting point of MgO (2800 °C) is lower than that of SiO2 (1600 °C).
44. In general, there must be anions in substances where there are cations; but in metals or alloys there are only cations and no anions, and the anionic part is replaced by free electrons.
45. The molecules that make up molecular crystals generally have covalent bonds; however, there are no covalent bonds in the molecules of noble gases, which are single-atom molecules.
46. Non-metallic oxides are generally molecular crystals when solid;
47. Elemental molecules are generally non-polar;
48. Active metal and reactive nonmetallic compounds are generally ionic compounds; but AlCl3 is a covalent compound formed by the combination of Al and Cl2.
49. Stable molecules need to satisfy an 8-electron (or 2-electron) structure; however, some molecules that do not satisfy the 8-electron structure can be stable, such as BF3.
50. The bond angle in the regular tetrahedral molecule is generally 109° 28'; however, the white phosphorus molecule is a regular tetrahedral structure, and its bond angle is 60°.
51. Wherever "reactions" are involved, chemical reactions generally occur;
Reversible reactions to volume changes before and after reactions, such as 2N2 +3H2
2NH3, when the chemical equilibrium is achieved under certain conditions in a closed container with a fixed volume, when other conditions remain unchanged, increasing the pressure can make the equilibrium move in the direction of reduced gas volume; but filled with "inert gas", the pressure in the closed container increases, but the equilibrium does not move.
2. Elements and compounds
1. Halogen elements generally do not react with rare gases, but F2 can react with rare gases such as Xe and Kr to generate corresponding fluorides, such as KrF2, XeF2, XeF4, XeF6, etc.
2. The common chemical equation for the reaction of halogen and water is generally: X2 + H2O = HX + HXO; but the chemical equation for the reaction of F2 with water is: 2F2 + 2H2O = 4HF + O2
3. The chemical equation for the reaction of halogen with a strong alkali solution is generally: X2 +2OH-=X- + XO- + H2O; but F2 reacts with water first when reacting with a strong alkali solution, and then reacts with the alkali.
4. Agx has photosensitivity and generally decomposes when seeing light; but AgF is stable and does not decompose when seeing light.
5. AgX is generally insoluble in water or dilute in HNO3; however, AgF is soluble in water.
CaX2 is generally soluble in water, but CaF2 is insoluble in water.
7. Halogens can show both negative and positive prices in compounds; but fluorine can only show negative prices in compounds.
8. The oxygen-free acid of halogen (hydrohalic acid) is generally a strong acid; but hydrofluoric acid is a weak acid.
9. Hydroacelic acid generally does not react with silicon or silicon dioxide; however, hydrofluoric acid can react with silicon or silicon dioxide.
10. The reaction of halogen elements with iron generally forms FeX3; however, the reaction product of I2 elements with iron is FeI2.
11. The melting and boiling points of substances with similar composition generally rise with the increase of relative molecular mass; however, the melting and boiling points of NH3, H2O and HF are abnormally elevated.
12. The density of alkali metal elements generally increases from top to bottom; but the density of potassium is smaller than that of sodium.
13. Alkali metals react with sufficient oxygen to generally produce peroxides or superoxides; but when Li reacts with O2, only Li2 can be generated.
14. When preparing reactive metals (such as K, Ca, Na, etc.), their molten salts are generally electrolyzed; but aluminum is the al2O3 melted in cryolite for electrolysis.
15. In metal sulfides, the compound price of sulfur is generally -2 valence; but the compound price of sulfur in FeS2 is -1 valence.
16. The main valence of carbon group elements is generally +2 and +4, but silicon is only +4.
17. The identification of PO43-ions can generally be carried out by the method of reagent AgNO3 solution, producing a yellow precipitate, and then diluting the HNO3 solution to precipitate and disappearing; however, the PO43-ion in phosphoric acid cannot be identified by the above method.
18. Non-metallic elements generally do not conduct electricity; but graphite and tellurium can conduct electricity.
19. Metals are generally solid at room temperature; but Hg is liquid.
20. Non-metallic elements are generally solid at room temperature;
21. The reaction of non-metallic elements with strong alkali solutions generally does not produce hydrogen; but silicon does not.
22. Barium salts (such as BaCO3, BaCl2, etc.) are generally extremely toxic, but BaSO4 is non-toxic, because it is insoluble in water or insoluble in stomach acid and is used as a barium meal.
23. Copper salt solutions are generally blue; however, gasified copper concentrate solutions are often green.
24. Acid salts are generally soluble in water; but monohydrogen phosphate is almost insoluble in water except for potassium, sodium, and ammonium salts.
25. Hydrogen generally shows a +1 valence in compounds, but -1 valence in metal hydrides, such as NaH, CaH2.
3. Organic chemistry
1. Organic matter generally contains carbon and hydrogen; however, the CCl4 composition does not contain hydrogen.
2. Organic matter is generally flammable; but carbon tetrachloride and polytetrafluoroethylene cannot be burned.
3. The organic product obtained by hydrolysis of halogenated hydrocarbons is generally alcohols; but the hydrolysis of gas benzene gives phenol.
Halogenated hydrocarbons are generally liquid and insoluble in water; however, monaerated alkanes are usually gases.
5. Catalytic oxidation of alcohols generally generates aldehydes (or ketones) and continues to oxidize to produce acids; however, R3COH cannot catalyze oxidation into aldehydes or acids.
6. Compounds that can be called "some acid" are generally acids; but phenol, commonly known as carbolic acid, does not belong to acids, but phenols.
7. Substances with molecular composition differences of one or several "-CH2-" groups are generally homologies, but benzyl alcohol is different from phenol, ethylene and cyclopropane, etc.
8. The organic matter that can undergo a silver mirror reaction is generally an aldehyde; but glucose, formic acid and a certain ester of formate can all undergo a silver mirror reaction.
9. The organic molecules that can undergo the silver mirror reaction generally contain aldehyde groups; but the fructose molecules do not contain aldehyde groups, and the silver mirror reaction can occur.
10. The reaction between acid and alcohol is generally an esterification reaction; however, the mixed heating of ethanol and hydrobromic acid to generate bromoethane is not an esterification reaction.
11. The esterification reaction generally occurs between the acid and the alcohol; but the esterification reaction can also occur between cellulose and concentrated HNO3.
12. Esters are generally prepared by esterification reaction between acids and alcohols; however, phenyl acetate is obtained by substitution reaction of acetic anhydride (CH3CO) 2O or acetyl ch3COC1 with phenol.
13. The oil in organic matter generally refers to the ester formed from fatty acids and glycerol; but gasoline, diesel, kerosene, etc. are complex mixtures of various alkanes, naphthenic hydrocarbons, aromatic hydrocarbons, etc.
14. The main component of wax generally refers to the ester formed by fatty acids and fatty alcohols; but paraffin wax is a mixture of high-grade alkanes (containing C20 ~ C30).
15. Isomers can generally be represented by the same chemical formula; but not all are represented, such as starch and cellulose.
16. Silk and hair generally refer to silk and animal hair, the components of which are proteins; but the component of rayon is cellulose, and rayon wool is synthetic fiber (polyacrylonitrile).
17. Glass generally refers to silicate; however, plexiglass is composed of polymethyl methacrylate.
4. Chemical experiments
1. The scale of the precision measuring instrument is generally either on the top (such as a burette) or under (such as a measuring cylinder); but the scale of the thermometer is lower in the middle.
2. The Qipu generator is suitable for bulk solids, liquids, and gases produced without heating (such as H2, H2S, CO2, etc.); but the Qipu generator cannot be used to make C2H2.
3. When preparing Cl2, HCl, NO and other gases, it is generally prepared by solid-solid, solid-one-liquid, and liquid-one-liquid generators; however, when making bromine and nitric acid, curved-necked koshiki should be used.
4. The cutting of solids should generally be carried out on the table; but the cutting of white phosphorus should be carried out in water.
5. After the drugs in the reagent bottle are removed, it is generally not allowed to put back the reagent bottle; but the remaining potassium, sodium, white phosphorus, etc. should be put back into the original bottle.
6. All kinds of waste liquid and waste in the experimental process should be put into the designated waste liquid tank or centralized treatment; however, the mercury accidentally spilled in the experiment should be collected or sprinkled with sulfur powder as much as possible to eliminate its toxicity.
7. The rubber head dropper generally cannot reach into the test tube to contact the inner wall of the test tube or the relevant container; however, when making Fe(OH)2 white precipitation, the dropper is extended into the test tube.
8. When absorbing easily soluble gases with water, the catheter should be close to the liquid level or connected to an inverted funnel, and the absorption of insoluble gaseous substances can be inserted into the water; however, when making ethyl acetate, the catheter is close to the liquid level of the saturated Na2CO3 solution, and cannot be inserted into it.
9. In the case of electrochemical corrosion, the metal with strong mobility generally corrodes first; but the aluminum ferroalloy, due to the protective effect of the aluminum surface with an oxide film, the iron first corrodes.
10. Neutral desiccant can generally be used to dry acidic, alkaline, neutral and other gases; but dry ammonia can not be selected anhydrous CaCl2.