When an aqueous solution of borax is acidified with HCl boric acid is formed
`Na_(2)B_(4)O_(7)+2HCl+5H_(2)Orarr2NaCl+underset("Boric acid")(4H_(3)BO_(3))`
Boric acid is a white crystalline solid. It is soapy to touch because of its planar layered structure. Boric acid is a weak monobasic acid. It is not a protonic acid but acts as a Lewis acid by accepting electrons from a hydroxyl ion
`B(OH)_(3)+2HOHrarr[B(OH)_(4)]^(-)+H_(3)O^(+)`.