To convert formaldehye to methanol :
Reduction reaction of aldehyde to give alcohols is used.
The reducing agent used is LiAlH4 or NaBH4.
The reducing agents LiAlH4 and NaBH4 act as a source of 4 x H- (hydride ion)
Overall 2 H atoms are added across the C=O to give H-C-O-H
Hydride reacts with the carbonyl group, C=O, in aldehydes o or ketones to give alcohols.
The substituents on the carbonyl dictate the nature of the product alcohol.
Reduction of methanal (formaldehyde) gives methanol.