Chemistry - Redox Reactions Question with Solution | TestHub

The balanced reaction is

$${\mathrm{K}}_2\mathrm{C}{\mathrm{r}}_2{\mathrm{O}}_7+4{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4+3{\mathrm{H}}_2{\mathrm{C}}_2{\mathrm{O}}_4⟶6C{\mathrm{O}}_2+7{\mathrm{H}}_2\mathrm{O}+\mathrm{C}{\mathrm{r}}_2(\mathrm{S}{\mathrm{O}}_4{)}_3+{\mathrm{K}}_2\mathrm{S}{\mathrm{O}}_4.$$

One mole of dichromate produces $6\times 22.4=134.4\mathrm{L}$ $\mathrm{C}{\mathrm{O}}_2$ at STP. The required mass is $294(5.6/134.4)=12.25\mathrm{g}$.