Concentrated commercial solutions of formaldehyde are 37-40% by weight of the gas formaldehyde dissolved in water.

• A. True
• B. False
• C. Not enough information
• D. Always

Answer: (A)

Formaldehyde sold for routine fixation is provided as an aqueous solution called formalin, where formaldehyde gas is dissolved in water. The typical concentration is about 37% by weight of formaldehyde, and many sources list a range up to 40%. The rest of the solution is water, and often a small amount of methanol is included as a stabilizer to prevent polymerization. Because this 37–40% formaldehyde in water range is the standard specification used in laboratories, the statement is true.