High school chemistry identification questions, high school chemistry identification questions.

The addition of caustic soda to produce gas indicates that the solution contains bicarbonate ions, and magnesium ions do not coexist with bicarbonate ions, so there is no magnesium chloride. Sodium carbonate is also absent because carbonate does not coexist with barium ions.

1.First, the properties of the substance are analyzed.

1) White precipitate appears when caustic soda is added, indicating the presence of some special metal ions;

2) The addition of dilute sulfuric acid produces a white precipitate - indicating the presence of soluble barium ions, and the gas indicates the presence of carbonate or bicarbonate;

2.Compare the given substance with the analytical information.

BACl2 – exists, consists of (2).

Na2CO3 – It does not coexist with MgCl2.

MgCl2 - precipitated by (1) white, magnesium ions must exist!

NaHCO3 – There is (2) the presence of gas Bing.

3.Check for known conditions.

Therefore, when encountering such problems, you must follow certain thinking steps, and this is what the conditions can launch. And there is a secondary school precipitation table, please refer to it.

May mine be helpful to you.

MgCl2 is possible. Because if there is no BaCl2, then the addition of dilute sulfuric acid will not produce precipitation.

Because magnesium ions and bicarbonate are dihydrolyzed, they cannot coexist. But what I didn't figure out was why adding caustic soda would produce gas.

First of all, there is gas production when adding acid and alkali, so there must be NaHCO3. There is a white precipitate with alkali, there may be MGCL2 and BACL2, and there is a precipitate with sulfuric acid, which means that there must be BACL2, so MGCL2 may or may not be there, uncertain. There must be a question question, it can only be bacl2.

You can add and remove mgcl2 to see if they all meet the requirements of the question, and if so, you are not sure.

The reason is that there are OH ions in caustic soda, and Mg(OH)2 is a red precipitate, which is obvious, but it is not mentioned in the title, so it is definitely not.

It may be because magnesium ions will be double hydrolyzed with bicarbonate and cannot coexist.

1) B, benzene does not react, in the upper layer of KMno4; 1-Hexene fades KMNO4; CCL4 does not react in the lower layer of KMNO4.

2) c, ethylbenzene does not react, delamination; Ethanol does not react, miscible and does not stratify; Acetic acid reacts to form gas;

3) e, benzene does not react, stratification; Phenol produces purple precipitates; NAOH produces red precipitates;

4) f, toluene does not react, stratify, and does not react after heating; Ethyl acetate does not react, stratification, after heating for a period of time, the reaction, delamination disappears; Ethylene glycol is miscible with it.

a. The key to identification is to have a phenomenon that is different from other substances.

Acetylsalicylic acid contains ester and carboxyl groups, which can react with sodium hydroxide without obvious phenomenon.

Eugenol contains phenolic hydroxyl groups and double bonds, which can appear purple with ferric chloride and can discolor bromine.

Cinnamic acid contains double bonds and carboxyl groups, which can discolor bromine and can also react with sodium hydroxide without obvious phenomenon.

The key to learning organic well is to grasp the nature of the various functional groups.

Common functional groups:

1 Carbon-carbon double bond: c=c 2 Carbon-carbon triple bond: c c

3 Halogen (fluorine, chlorine, bromine, iodine) atoms: —x 4 (alcohol, phenol) hydroxyl group: —OH

5 Aldehyde group: —CHO 6 Carboxyl group: —COOH 7 ester group: —COO—

Alkane CNH2N+2 only contains C-C bond substitution reaction with halogens, thermal decomposition, and does not react with potassium permanganate, bromine water, strong acid and strong alkali.

Olefin CNH2N contains C=C bond and has addition reaction with halogens, oxidation reaction with potassium permanganate, polymerization reaction, and polyaddition reaction.

The alkyne CNH2N-2 contains C and C bonds, and undergoes addition reaction with halogens, oxidation reaction and polymerization reaction with potassium permanganate.

Benzene (aromatic hydrocarbon) CNH2N-6 undergoes substitution reaction with halogens and other elements, and additions with hydrogen and other gases (benzene homologues such as toluene and ethylbenzene can oxidize with potassium permanganate).

Halogenated hydrocarbons: CNH2N+1X substitution reaction (hydrolysis) and elimination reaction.

Alcohol: CNH2N+1OH or CNH2N+2O substitution reaction (including esterification reaction), elimination reaction, oxidation reaction, phenol: weakly acidic, purple color when encountering FeCl3 solution.

Aldehyde: CNH2NO oxidation reaction, reduction reaction.

Carboxylic acid: CNH2NO2 acidification and esterification reaction.

Ester:CNH2NO2 hydrolysis reaction.

Choose a eugenol has a phenolic hydroxyl group, which can be colored with iron chloride.

Cinnamic acid has a carbon-carbon double bond that can be added to bromine.

Select a eugenol has a phenolic hydroxyl group, which can be purple with ferric chloride, which can fade the carbon tetrachloride solution of bromine.

Cinnamic acid has a carbon-carbon double bond, which can be added with bromine and can discolor the carbon tetrachloride solution of bromine.

Acetylsalicylic acid is to react, but there is no obvious phenomenon.

Select the B exclusion method.

1.If the total volume is 1 16 of the volume of hydrogen of the same mass under the same conditions, the density should be 16 times that of hydrogen under the same conditions, and the average molecular weight of the good consumption should also be 16 times that of H2, that is, 32.

2.Only those with a molecular weight smaller than 32 and those larger than 32 can be mixed to produce an average of 32.

Therefore the 4 options, CH4 and C2H4 in A, have a molecular weight below 32 and are excluded;

C, C3H8 molecular weight 44, C4H8 molecular weight 56, both greater than 32, also excluded;

C4H10 and C5H10 are both greater than 32 in D, which is also excluded;

The remaining B C2H6 molecular weight is 30, and C3H6 is 42, which can make the average stove stuffiness value of 32, so B is selected.