Physical properties Urea is easily soluble in water, 105 grams can be dissolved in 100 ml of water at 20℃, and the aqueous solution is neutral。There are two types of urea products。Crystalline urea is white needle-like or prismatic crystal shape, strong hygroscopicity, caking after hygroscopicity, hygroscopicity rate is 12 times faster than granular urea。 Granular urea is a translucent particle with a particle size of 1 ~ 2 mm, the appearance is smooth, and the hygroscopicity has been significantly improved。At 20℃, the critical hygroscopic point is 80% relative humidity, but at 30℃, the critical hygroscopic point drops to 72.5%, so urea should avoid open storage in the humid climate of midsummer。When hydrophobic substances such as paraffin wax are added to urea production, its hygroscopic property is greatly reduced。

　　Chemical property

　　Urea Urea reacts with acids to form salts。hydrolytic。Condensation can be performed at high temperatures to produce biuret, triuret and cyanic acid。Heating to 160℃ decomposition, producing ammonia gas and isocyanic acid。Because this substance is found in human urine, it is named urea。Urea contains 46% nitrogen (N), which is the highest nitrogen content among solid nitrogen fertilizers。

　　Urea can be hydrolyzed to produce ammonia and carbon dioxide under the action of acids, bases and enzymes (acids and bases need to be heated)。

　　It is not stable to heat, and will be deammoniated into biuret when heated to 150~160℃。Copper sulfate and biuret reaction purple, can be used to identify urea。 If rapidly heated, it will be deammoniated and trimerized into the six-membered cyclic compound cyanic acid。[Mechanism: First deamination to isocyanic acid (HN=C=O), repeated polymerization。】

　　Reaction with acetyl chloride or acetic anhydride can produce acetylurea and diacetylurea。Under the action of sodium ethanolate, it reacts with diethyl malonate to form malonyl urea (also known as barbituric acid, because of its acidity).。Under the action of alkaline catalyst such as ammonia water, it can react with formaldehyde and condense into urea-formaldehyde resin。It reacts with hydrazine hydrate to form semicarbazone。