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[Visitor (112.21.*.*)]answers [Chinese ]Time :2022-01-17
Molecular structure of formaldehyde

Carbon atoms form three σ bonds in three sp² hybrid orbitals. One of them is to form a σ bond with oxygen. These three keys are on the same plane. One p-orbital of a carbon atom and one p-orbital of oxygen overlap each other to form a π bond. Perpendicular to the plane formed by these three σ keys. Key angle ∠HCH=111.5°, ∠HCO=121.8°. Key length C-H 120.3pm, C-O 110pm. Dipole moment 7.56×10⁻³ºC·m.

Physicochemical properties of formaldehyde
Colorless aqueous solution or gas with a pungent odor. It can be miscible with organic solvents such as water, ethanol, and acetone in any proportion. The liquid is easily cloudy when it is cold, and forms a trimaldehyde precipitate at low temperatures. Some formaldehyde escapes when evaporating, but most of it becomes formaldehyde. The product is a strong reducing agent, which is more reducible when it is slightly alkaline. It can be slowly oxidized into formic acid in air.

Vapour relative density 1.081-1.085 g/mL (air = 1), relative density 0.82 g/mL (water = 1), refractive index (nD₂₀) 1.3755-1.3775, flash point 56 °C (gas), 83 °C (37% aqueous solution, closed cup), boiling point -19.5 °C (gas), 98 °C (37% aqueous solution), melting point -92 °C, auto-ignition temperature 430 °C, Vapor pressure 13.33kPa (-57.3 °C), explosion limit air 7%-73%, V/V.
Octanol-water partition coefficient 0.35, critical temperature 137.2~141.2 °C, critical pressure 6.784 ~6.637 MPa, viscosity 0.242 mPa·s (-20 °C).

It is easily soluble in water and ether, and the concentration of aqueous solution can reach up to 55%. It can be miscible with water, ethanol and acetone. In the air, it can be gradually oxidized to formic acid, which is a strong reducing agent. Its vapor forms an explosive mixture with air, which can cause combustion explosions in the presence of open flames and high heat energy. In general commodities, 10% to 12% methanol is added as an inhibitor, otherwise polymerization will occur.

pH: 2.8~4.0, flash point: 60°C

Chemical properties: Pure formaldehyde has a strong reducing effect, especially in alkali solutions. Formaldehyde itself can slowly carry out condensation reactions, and it is particularly prone to polymerization reactions.
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