Question

How do you prepare \(Na_2Cr_2O_7\) from \(Na_2CrO_4\) ?

Answer 1

Preparation of Sodium Dichromate

Preparation of Sodium Dichromate (\({Na2Cr2O7}\))

Sodium dichromate (\({Na2Cr2O7}\)) can be prepared from sodium chromate (\({Na2CrO4}\)) by acidifying the chromate solution using sulfuric acid (\({H2SO4}\)).

Upon acidification, chromate ions (\({CrO4^{2-}}\)) are converted into dichromate ions (\({Cr2O7^{2-}}\)), and sodium dichromate precipitates.

Balanced Chemical Equation:

\[ 2{Na2CrO4} + {H2SO4} \rightarrow {Na2Cr2O7} + {H2O} + {Na2SO4} \]

Note: If the simplified reaction is written omitting side products:

\[ {Na2CrO4} + 2{H2SO4} \rightarrow {Na2Cr2O7} + {H2O} \]

This process involves an equilibrium shift from yellow chromate (\({CrO4^{2-}}\)) to orange dichromate (\({Cr2O7^{2-}}\)) in acidic conditions.