Identification method for high concentration sulfuric acid:

1. Weighing method

Concentrated sulfuric acid has a higher density than dilute sulfuric acid (98% concentrated sulfuric acid has a density of 1.84g/mL), so at the same volume, the heavier one is concentrated sulfuric acid.

2. Viscosity method

Concentrated sulfuric acid is a viscous liquid, while dilute sulfuric acid is close to the viscosity of water. Therefore, by shaking the reagent bottle a few times, one can see which one is concentrated sulfuric acid. When the liquid is full, a small amount can be shaken in the test tube. However, it is not recommended to use it when there is no comparison.

3. Boiling point method

Sulfuric acid is an acid with a high boiling point, and 98% concentrated sulfuric acid has a boiling point of 338 ℃. Therefore, a small amount of sulfuric acid can be heated in a test tube. If it boils first and a large amount of water vapor is generated, it is called dilute sulfuric acid. Be careful not to inhale steam, as a small amount of acid will evaporate with water. What is difficult to boil is concentrated sulfuric acid.

4. Dilution method

Slowly inject concentrated sulfuric acid into the water along the vessel wall and continuously stir. (Do not inject water into concentrated sulfuric acid, as this will cause droplets to splash. Explanation: The density of water is small, and water will float on top of concentrated sulfuric acid. The heat released during dissolution causes the water to boil, causing droplets to splash, which is very dangerous.) When diluting, a large amount of heat is released from concentrated sulfuric acid

5. Iron aluminum method

Take a small amount of it separately into the test tube and add iron wire or aluminum sheet. If there is no phenomenon, it is concentrated sulfuric acid, and if there are bubbles, it is dilute sulfuric acid. Because concentrated sulfuric acid can quickly oxidize the surface of metals such as iron and aluminum at room temperature to form a dense oxide film and cause "passivation", adding a small amount of chloride ions to the sulfuric acid solution will catalyze the decomposition of the oxide film. One theory is that chloride ions form a complex with the oxide film, and another theory is that the radius of chloride ions is smaller than the interval between oxide molecules, and chloride ions can enter the interior of the oxide film and continue to participate in the reaction.

6. Copper carbon method

Take two test tubes separately, add copper or charcoal, add acid separately, and then heat them to produce a stimulating gas called concentrated sulfuric acid. The irritating gas is sulfur dioxide.

7. Bile alum method

Take two test tubes separately, add a little bile alum, and then add acid separately. Dilute sulfuric acid turns blue in the crystal dissolution solution, and concentrated sulfuric acid turns white on the crystal surface. This change is both a physical and a chemical change.

8. Cellulose method

Dip two types of acids into a glass rod and make marks on paper, wood, or cotton cloth. After a period of time, the surface dehydrates, carbonizes, and turns black with concentrated sulfuric acid.

9. Sucrose method

Add about 10g of sucrose to a small beaker, drop 1mL of water, and then add acid. Concentrated sulfuric acid can dehydrate and carbonize the sucrose to produce "black bread". In this reaction, concentrated sulfuric acid and water are used to promote the reaction by releasing heat, and water is used as a catalyst.

10. Exposed method

Concentrated sulfuric acid has water absorption properties. After being exposed for a period of time, the mass of concentrated sulfuric acid increases, while dilute sulfuric acid may decrease due to the evaporation of water

11. Sodium nitrite method

Add a small amount of industrial salt to the test tube, and then add acid separately. Concentrated sulfuric acid produces irritating gas and red gas, while dilute sulfuric acid is produced when industrial salt dissolves non irritating gas. The main irritating gases are nitrogen dioxide and sulfur dioxide.

12. Conductivity method

Take two carbon rods as electrodes and insert them into the acid. Connect a small light bulb in series in the circuit, and use two dry batteries to form a closed circuit. The small light bulb emits light and the brighter one is dilute sulfuric acid. Because there is less water in concentrated sulfuric acid, the majority of sulfuric acid molecules are not ionized, so there are few freely moving ions and the conductivity is poor. However, concentrated sulfuric acid can react with carbon, so inert metal wires such as tantalum should be used as electrodes. (Note: Concentrated sulfuric acid has weak conductivity due to self ionization of 2H2SO4=reversible=H3SO4++HSO4- producing freely moving ions [1])

13. Sodium chloride method

Add a small amount of sodium chloride to two test tubes, and then add acid separately. Concentrated sulfuric acid produces a pungent odor gas, while dilute sulfuric acid produces a non pungent odor gas when sodium chloride dissolves. Sodium chloride reacts with concentrated sulfuric acid to produce sodium sulfate and a gas with a pungent odor, hydrogen chloride

High concentration sulfuric acid