About chemistry in junior high school! Questions about junior high school chemistry

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Dilute sulfuric acid does not react with sodium chloride, it is produced by gas with sodium carbonate, and barium nitrate is produced by barium sulfate precipitation.

2.Dilute sulfuric acid cannot be used, because dilute sulfuric acid can also react with NaOH and fail to remove impurities, and new impurities are introduced. An appropriate amount of Ca(OH)2 should be used to remove Na2CO3

1. Barium nitrate is precipitated, and sodium carbonate is bubbled.

H2SO4 + Na2CO3 = Na2SO4 + H2O + CO2BA(NO3)2 + H2SO4 = BaSO4 + 2HNO32 cannot, sulfuric acid reacts with NaOH.

1. Sodium carbonate, which produces gas; barium nitrate, which produces a white precipitate; The rest is sodium chloride.

2. No, you can't. Because dilute sulfuric acid can also react with sodium hydroxide, the required substances are also removed.

1. Dilute sulfuric acid does not react with sodium chloride, produces carbon dioxide gas with sodium carbonate, and forms barium sulfate with barium nitrate to precipitate.

2. Dilute sulfuric acid reacts with sodium hydroxide and sodium carbonate at the same time.

1. Dilute sulfuric acid does not react with sodium chloride, and there is no phenomenon.

Dilute sulfuric acid reacts with sodium carbonate to release carbon dioxide, and bubbles produce dilute sulfuric acid reacts with barium nitrate to form barium sulfate precipitate insoluble in nitric acid 2 The basic requirement for removing impurities is that the reagent does not introduce new impurities, let alone reflect the substances to be purified.

Dilute sulfuric acid will react with NaOH first.

Endothermic reactions: most of the decomposition reactions, C, Co, H2 reduction of metal oxides, barium hydroxide with eight crystal water and ammonium chloride reaction, most of the salt hydrolysis reactions, a few chemical reactions (generally not required to master).

Exothermic reactions: most of the chemical reactions, acid-base neutralization reactions, metal and acid reactions, metal and water reactions, combustion reactions, ** reactions.

Exothermic concentrated sulfuric acid, sodium hydroxide solid NaOH...

Endothermic ammonium nitrate NH4NO3

Glucose C6H12O6... In junior high school, remember that ammonium nitrate absorbs heat when it encounters water, such as active metal, strong alkali, and concentrated sulfuric acid to extothermic.

Many of the things people use now are organic synthetic materials, such as many glasses are made of plexiglass, of course, the windows and tires on the car, the plastic bags used in life, the chassis on the induction cooker, etc. It can be said that organic synthetic materials have been able to replace the high-temperature functional role of some metals in many aspects! Plastics, rubber, and man-made fibers are all organic synthetic materials.

General combustion and spontaneous reactions (without external additional conditions) are exothermic reactions, such as the combustion of Cs P Mg in air, and the endothermic reaction of Zn and hydrochloric acid, the common CaCO3 to CaO

C+H2O=CO+H2 decomposition reaction is generally an endothermic reaction, such as 2NaHCO3 (heating) Na2CO3+H2O+CO2. Note: Reactions that do not require heating are endothermic reactions, and most of the combustion reactions are "ignited", which are exothermic reactions.

An endothermic reaction is a reaction that continuously absorbs a large amount of heat during chemical changes. It is not necessary that only the reactions that use a catalyst are endothermic reactions, and C+CO2=2CO is an endothermic reaction.

Common exothermic reactions:

The reaction of metal with water or with acid to produce hydrogen, such as Na, K and H2O, Al, Mg, Zn and HCl, most of the chemical reactions, such as SO3+H2O, CAO+H2O, ammonia synthesis is exothermic, SO2 O2, neutralization reaction.

All combustion reactions, combustion of CH4, C2H4, C2H2, combustion of H2 in Cl2, etc.

Common endothermic reactions.

Most of the decomposition reactions.

The reaction of ammonium salt with alkali (Ba(OH)2 8H2O NH4Cl can only be carried out by continuous high temperature heating.

Hydrolysis of salts.

Ionization of weak electrolytes.

Some special chemical reactions: C+CO2, N2 O2, H2 I2 exothermic: concentrated sulfuric acid, sodium hydroxide, quicklime, etc.

Endothermic: ammonium nitrate, ammonium chloride and other ammonium salts.

Plastics, rubber, and man-made fibers are all organic synthetic materials.

According to the mass relationship in the reaction of 2H2+O2=2H2O, every 4 parts of hydrogen reacts with 32 parts of oxygen to produce 36 parts of water. So there is a surplus of hydrogen in this question, so it is calculated with oxygen.

Consumption of oxygen and production of water.

2g xg32 2g = 36 xg gets x=

The mass ratio of hydrogen to oxygen in water is 2:16 = 1:8

The hydrogen corresponding to 2g of oxygen is.