A chemical derived from tin, just about (5)
I believe the answer is:
nitre
'a chemical' is the definition.
(I've seen this before)
'derived from tin just about' is the wordplay.
'derived from' is an anagram indicator.
'just about' becomes 're' (regarding. I am not sure about the 'just' bit.).
'tin' is an anagram of 'nit'.
'nit'+'re'='NITRE'
Can you help me to learn more?
(Other definitions for nitre that I've seen before include "Salt" , "Inert (anag) - saltpetre" , "explosive component" , "Otherwise saltpetre" , "food preservative" .)