[funlovin]

In the lab,we prepared chromic acid by dissolving sodium dichromate in water with the addition of conc. H2SO4.I try to write the rxn but i could not.The molecular formula of chromic acid is H2CrO4 in Solomons but in some sites i found that it is H2Cr2O7 and CrO3.Can someone help me?Which one is correct?

[Dan]

You have a mixture of various Cr(VI) species such as H₂CrO₄ and H₂Cr₂O₇

CrO₃ is the anhydride ("minus water") form of chromic acid:

CrO₃ + H₂O ----> H₂CrO₄

H₂Cr₂O₇ + H₂O <---> 2H₂CrO₄

H₂CrO₄ and H₂Cr₂O₇ are both acceptable formulas for aqueous chromic acid.
.

[funlovin]

Na2Cr2O7 + H2SO4 ---> H2Cr2O7 + Na2SO4

H2Cr2O7-->H2crO4 +CrO3
is the rxn correct ?

[Dan]

H2Cr2O7-->H2crO4 +CrO3
is the rxn correct ?

Yes it's certainly along the right lines

Two things:

1. This is an equilibrium, so make sure you write it as such

2. CrO₃ itsself probably won't exist (to a large extent) in aqueous solution but will become hydrated:

CrO₃ + H₂O <---> H₂CrO₄

This equilibrium lies far to the left side in aqueous solution