FeSO4.7H2O. Caution: harmful if swallowed. Appropriate quantity as a replacement for chemistry set chemical. Image for illustration only, actual product may appear different.
Iron(II) sulfate (Iron(II) sulphate) or ferrous sulfate (ferrous sulphate) is the chemical compound with the formula (FeSO4), known since ancient times as copperas. It is most commonly encountered as the blue-green heptahydrate.
Image & text from Wikipedia.