Question

carbon dioxide is removed by scrubbing the mixture with with sodium arsenite (na3aso3) solution

Answer 1

This reaction in chemistry is known as "Water gas shift reaction ". Here sodium arsenite solution is act as catalyst.

There is a redox mechanism involved in formation of CO2 from water gas. It involves a regenerative change in the oxidation state of the catalytic metal. In sodium arsenite solution, arsenic undergoes the regenerative change in oxidation state. There are 2 different mechanism proposed in literature. In one case, H2O is activated first by the abstraction of H from water followed by dissociation or disproportionation of the resulting OH to afford atomic O. The CO is then oxidized by the atomic O forming CO2 .

In second case  CO directly oxidized by the OH to form a carboxyl intermediate, followed by the dissociation or disproportionation of the carboxyl. Finally H is recombined to form H2 and CO2​.