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2017 College Entrance Examination Chemistry Knowledge Points

1. Mistakenly believe that organic matter is easy to burn. For example, carbon tetrachloride is not easy to burn and is an efficient fire extinguishing agent.

2. It is mistakenly believed that methylene chloride has two structures. Because methane does not have a planar structure but a regular tetrahedral structure, methylene chloride has only one structure.

3. It is mistakenly believed that hydrocarbons with more than 4 carbon atoms are liquid or solid at normal temperature and pressure. The exception is neopentane, which has a boiling point of 9.5°C and is a gas.

4. It is mistakenly believed that acidic potassium permanganate solution can be used to remove ethylene from methane. Ethylene is oxidized by acidic potassium permanganate to produce carbon dioxide, so the purpose of impurity removal cannot be achieved and must be treated with soda lime.

5. It is mistakenly believed that the double bond has small bond energy, is unstable, and is easy to break. In fact, only one of the double bonds meets the above conditions.

6. Mistakenly believing that polyethylene is a pure substance. Polyethylenes are mixtures because their relative molecular masses are variable.

7. It is mistakenly believed that acetylene reacts faster with bromine water or acidic potassium permanganate solution than ethylene. It is well established that acetylene discolors them much more slowly than ethylene.

8. It is mistakenly believed that methane and chlorine can undergo substitution reactions under light, so benzene and chlorine can also undergo substitution under light (ultraviolet) conditions. The addition reaction between benzene and chlorine under ultraviolet irradiation produces hexachlorocyclohexane.

9. It is mistakenly believed that benzene and bromine water do not react, so there is no obvious phenomenon after mixing the two. Although the two do not react, benzene can extract bromine from the water, so the color of the water layer becomes lighter or fades, while the benzene layer turns orange-red.

10. It is mistakenly believed that toluene in benzene can be removed by using acidic potassium permanganate solution. Toluene is oxidized into benzoic acid, and benzoic acid is easily soluble in benzene, but it is still difficult to separate. Sodium hydroxide solution should be used to convert benzoic acid into water-soluble sodium benzoate, and then the liquids should be separated.

11. Mistakenly believing that the fraction obtained after petroleum fractionation is a pure substance. The products of fractionation are fractions within a certain boiling point range because of the mixture.

12. It is mistakenly believed that acidic potassium permanganate solution can distinguish between straight-run gasoline and cracked gasoline. Straight-run gasoline contains more benzene homologues; the two cannot be identified by acidic potassium permanganate.

13. It is mistakenly believed that halogenated hydrocarbons must undergo elimination reactions.

14. It is mistakenly believed that organic substances connected with hydrocarbon groups and hydroxyl groups must be alcohols. Phenol is a phenol.

15. Mistakenly believe that ethanol is a liquid and phenol is a solid. Phenol does not react with metallic sodium. Although solid phenol does not react with sodium, it can react with sodium when phenol is melted, and the reaction is more violent than ethanol and sodium.

16. It is mistakenly believed that phenol is less acidic than carbonic acid, so phenol cannot react with sodium carbonate solution. Although the ionization degree of phenol is smaller than that of carbonic acid, it is larger than that of bicarbonate ion. Therefore, it can be seen from the metathesis law that phenol and sodium carbonate solution can react to form sodium phenolate and sodium bicarbonate.

17. It is mistakenly thought that if you want to remove phenol from benzene, you can add enough concentrated bromine water to it, and then filter out the resulting precipitate. After the reaction of phenol and bromine water, the excess bromine is easily extracted into benzene, and although the generated tribromophenol is insoluble in water, it is easily soluble in benzene, so the purpose cannot be achieved.

18. It is mistakenly believed that only alcohols can form esters, but phenols cannot form esters. Phenols can also form corresponding esters, such as aspirin, which is a phenolic ester. However, compared with alcohols, phenol is more difficult to form esters. It usually reacts with carboxylic acid anhydrides or acid chlorides to form esters.

19. It is mistakenly believed that alcohol must undergo dehydrogenation and oxidation. Alcohols whose carbon is quaternary cannot be dehydrogenated, such as neopentyl alcohol.

20. It is mistakenly believed that aldehydes must be generated when saturated monohydric alcohols are oxidized. When the hydroxyl group is attached to a tertiary carbon, it is oxidized to a ketone, such as 2-propanol.

21. It is mistakenly believed that alcohol can definitely undergo elimination reaction. Methanol and alcohols without hydrogen at adjacent carbon atoms cannot undergo elimination reactions.

22. It is mistakenly believed that the organic matter produced by the reaction of acid and alcohol must be an ester. The bromoethane produced by the reaction of ethanol and hydrobromic acid is a halogenated hydrocarbon, not an ester.

23. It is mistakenly believed that the esterification reaction must be "acid removal of hydroxyl and alcohol dehydrogenation". When ethanol reacts with inorganic acids such as nitric acid, alcohol is generally dehydroxylated and acid is dehydrogenated.

24. It is mistakenly believed that all organic compounds containing carboxyl groups in the molecules must be carboxylic acids, which can make litmus red. Stearic acid cannot turn litmus red. 25. It is mistakenly believed that the reaction that can introduce nitro groups into organic molecules must be nitration reaction. The esterification reaction between ethanol and concentrated nitric acid produces ethyl nitrate.

26. Mistakenly believe that organic substances with the same simplest formula but different molecular structures are isomers. Examples: formaldehyde, acetic acid, glucose, methyl formate (CH2O); ethylene, benzene (CH).

27. It is mistakenly believed that organic substances with the same relative molecular mass but different molecular structures must be isomers.

Example: Ethane and formaldehyde, propanol and acetic acid have the same relative molecular mass but different structures, but are not isomers.

28. It is mistakenly believed that organic substances with the same relative molecular mass, the same constituent elements, and different molecular structures must be isomers. Example: ethanol and formic acid.

29. It is mistakenly believed that substances whose molecular composition differs by one or several CH2 atomic groups must be homologues. Example: ethylene and cyclopropane.

30. It is mistakenly believed that organic substances that can undergo silver mirror reaction must be aldehydes or must contain aldehyde groups. Glucose, formic acid, and a certain ester of formic acid can undergo a silver mirror reaction, but they are not aldehydes; fructose can undergo a silver mirror reaction, but it is a polyhydroxy ketone and does not contain an aldehyde group.